ProSoundWeb Community

Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => SR Forum Archives => LAB Lounge FUD Forum Archive => Topic started by: Alexander B Larsson on February 05, 2008, 11:11:42 am

Title: Subwoofer amps - what are we REALLY hearing?
Post by: Alexander B Larsson on February 05, 2008, 11:11:42 am
I am still searching for that "big amp" for the bass boxes, but the more I read, the more contradictory the information seems...
I currently run a number of older "conventional PSU" Labgruppen amps, but having one bridged amp per driver is HEAVY!  Confused

(Finding amps for listening tests is somewhat hard in Sweden, as many of the MI shops carry only entry level stuff, like Phonic, Alesis etc.)

Normally one can find some general trends in opininons/reviews of stuff, but amps seem different? Strange, since they should actually have the smallest impact on overall fidelity of the rig, from a distorsion point of view.

Some praise the QSC RMX 4050 and 5050 for subs, while some claim their upgrade from RMX to some "switched" Crown, Lab or similar made a world of difference. Listening test (shootout) says the differences are small, but that test only included few speakers, etc...

Considering our ear's limited sensitivity to detect distorsion in the bass range, what IS it that we hear?

A guy I talked to described the lightweight Lab amps as "punchy" in the bass, but are we talking about that amp adding something that was not originally there? Or are many other amps missing the "punch", whatever that would be?

Power is clearly important, but amps that run below their clipping point should not colour sound at all, at least not detectable...

/Alexander
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Duncan McLennan on February 05, 2008, 11:22:54 am
I've personally always like amplifiers with real toroidal transformers and linear power supplies.  Switching amps, although convenient for weight purposes, have never sounded as good to my ear.  That might be just me.

So is weight worth sacrificing sound quality?  I don't know.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Nathan Schwarzkopf on February 05, 2008, 12:26:48 pm
Hay alex

I have beat this to death in my own head and a little on this board as well.

I have tried a ton of different "solutions".  

I started with a rmx 5050-linear- and in my case they turned out to be total junk and sounded like ass.  So I switched to the plx 3402-switcher- Which at the time I thought I had found THE amp.  Then I discovered the 8001-linear- and guess what I fell in love again. Then came the 9200-switcher- and now I am on 10001's-linear.

We are currently in an ongoing debate about this in the shop with MC2 and 8001's also.  What it really boils down to IMO is that every am will "color" the sound.  I feel that the switchers do it less than the linear's but in some cases it is almost a desired effect.  I am on the linear boat again on the low end because there just seems to be more drive and guts for lack of a better description.  Your just going to have to take stuff out for a spin and see how ya like it.

Nathan
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Scott Smith on February 05, 2008, 12:46:52 pm
Alexander B Larsson wrote on Tue, 05 February 2008 11:11

I am still searching for that "big amp" for the bass boxes, but the more I read, the more contradictory the information seems...

Yes...there does seem to be a lot of "contradictory" information out there.  

I went from a PLX3402 amp to a PL6.0 running stereo...and at any level I hear better dynamics and get punchier bass.  While I know the PL6.0 has a much beefier power supply, no one has ever been able to technically explain why this amp has a damping factor of 2000.  All people will say is that this figure is just "marketing hype" and means nothing.  Is it possible the figure is the result of the beefier power supply?

My feeling regarding this issue IS NOT supported by anyone here, or the stack of technical facts that can be provided against my beliefs.  But I know what I hear...so do most people using this amp, or other big ones like it.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Bennett Prescott on February 05, 2008, 12:57:50 pm
You have to be using the right kick drum mic to go with it, of course.

My advice: Run the biggest amp you can.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Chuck Fry on February 05, 2008, 01:09:11 pm
Scott Smith wrote on Tue, 05 February 2008 09:46

While I know the PL6.0 has a much beefier power supply, no one has ever been able to technically explain why this amp has a damping factor of 2000.  All people will say is that this figure is just "marketing hype" and means nothing.  Is it possible the figure is the result of the beefier power supply?


That damping factor is only relevant if you have the driver connected directly at the amplifier's output terminals. Use any length of cable and it's degraded. I tend to agree that high damping factors are primarily marketing hype and of little practical use.

My limited understanding is that the damping factor is more a result of a high feedback factor, and minimal impedance between the output stage and the terminals, than it is a function of the power supply.

I would love to see someone do double-blind testing of power amps at the next sub shootout.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Scott Smith on February 05, 2008, 01:23:03 pm
Chuck Fry wrote on Tue, 05 February 2008 13:09

...My limited understanding is that the damping factor is more a result of a high feedback factor, and minimal impedance between the output stage and the terminals, than it is a function of the power supply...

Ah yes... but isn't the job of the amplifier to ultimately get the power (from the power supply) to the speakers with the least amount of resistance and loss?
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Ryan Lantzy on February 05, 2008, 01:27:27 pm
Scott Smith wrote on Tue, 05 February 2008 13:23

Chuck Fry wrote on Tue, 05 February 2008 13:09

...My limited understanding is that the damping factor is more a result of a high feedback factor, and minimal impedance between the output stage and the terminals, than it is a function of the power supply...

Ah yes... but isn't the job of the amplifier to ultimately get the power (from the power supply) to the speakers with the least amount of resistance and loss?


I hate to even acknowledge this with a reply... but here goes.

FOR THE LAST TIME, THE DAMPING FACTOR OF AN AMP CAN DO NOTHING TO IMPROVE THE DAMAGE THE COPPER IN BETWEEN DOES TO THE DAMPING FACTOR!

It's VERY simple math.  Look into it.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Scott Smith on February 05, 2008, 01:33:45 pm
Reply as loud as you like...  I already said my belief is NOT supported. Cool
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Alexander B Larsson on February 05, 2008, 01:46:21 pm
Thanks for all the replies!

Don't you find it frustrating that we in this case not can quantify what we hear? And that amps that on paper are indistinguishable still do not sound the same, even within their linear operation (as in no clipping/current limiting).
Or do we fool ourselves - how big are the differences?

A few years ago I had the opportunity to pick up either of two Labgruppen amps for my bass guitar rig. One Lab 1000 or one Lab 1300. They are VERY close in spec, with most of the design the same, except the power supply. (The 1000 is a conventional and the 1300 is switched.) The price was the same, making the 1300 a bargain, as it is normally more expensive. However, there was no doubt the two bottom octaves where better with the Lab 1000.

And I have to carry the 20 or so extra pounds every time I move the thing...

/Alexander
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: John Roberts {JR} on February 05, 2008, 02:05:55 pm
Alexander B Larsson wrote on Tue, 05 February 2008 12:46

Thanks for all the replies!

Don't you find it frustrating that we in this case not can quantify what we hear? And that amps that on paper are indistinguishable still do not sound the same, even within their linear operation (as in no clipping/current limiting).
Or do we fool ourselves - how big are the differences?

A few years ago I had the opportunity to pick up either of two Labgruppen amps for my bass guitar rig. One Lab 1000 or one Lab 1300. They are VERY close in spec, with most of the design the same, except the power supply. (The 1000 is a conventional and the 1300 is switched.) The price was the same, making the 1300 a bargain, as it is normally more expensive. However, there was no doubt the two bottom octaves where better with the Lab 1000.

And I have to carry the 20 or so extra pounds every time I move the thing...

/Alexander


It is disappointing that many unscientific and subjective observations confuse the understanding.  

I submit that in fact any difference you hear between amplifiers is non-linear behavior.  Clipping, current limiting, etc are far more common than people estimate. Even frequency response errors are nonlinear.

Clip limiters will also have a characteristic sound signature.

I don't deny that there are differences between amplifier in practice, but it's not all that mysterious. If the specs don't explain the differences you hear, you are looking at the wrong specs, or some other than controlled bench test situation.

JR




Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: John Roberts {JR} on February 05, 2008, 02:24:53 pm
Ryan Lantzy wrote on Tue, 05 February 2008 12:27



I hate to even acknowledge this with a reply... but here goes.

FOR THE LAST TIME, THE DAMPING FACTOR OF AN AMP CAN DO NOTHING TO IMPROVE THE DAMAGE THE COPPER IN BETWEEN DOES TO THE DAMPING FACTOR!

It's VERY simple math.  Look into it.


In the interest of accuracy. I am familiar with a technology at Peavey that was intended to deliver arbitrarily high numerical damping factors (>3000:1). This circuit actually had the capability to deliver a "negative output impedance" so in fact this could actually compensate for copper (voltage not power) losses in speaker wire.

This technology was abandoned because it was a just a specifications number game and didn't deliver a real benefit to customers.  

So I agree with the thrust of your rant, but I would word it a little differently. "Damping factor is IMO not audibly significant in modern solid state amplifiers".

JR
Title: Sound Is Subjective
Post by: Elliot Thompson on February 05, 2008, 02:49:17 pm
Alexander B Larsson wrote on Tue, 05 February 2008 16:11



Considering our ear's limited sensitivity to detect distorsion in the bass range, what IS it that we hear?



/Alexander



What "We hear" is subjective based on what we are looking for.

Top cabinets play a heavy factor which is always overlooked. This is why, even at a Sub woofer Shootout you cannot get a full understanding of the subs performance. Sure, it sounds good on the system being used. However, will it sound that way on your amps sitting below your top cabinets.

We also need to keep in mind what you and I hear can be totally different based on what we are focusing on, when we listen to the whole ensemble. Some just want the room to fill up with bass. Some want more punchy bass. Some want more extended bass. Some want to hear a particular frequency they've grown accustomed to from their own rig using xyz amplifier.

All amps offer their own characteristic when loaded with a particular sub cabinet. This is based on my experience owning Crest, Crown, QSC,  Peavey and a few other amplifier brands. How we decipher that sound in addition to whether it sounds pleasing or not is solely up to us to decide. For again, we are not listening to only the sub woofer – amp combo. We are listening to the complete system with the sub woofer – amp combo.

What I'm basically saying is trust your ears, understand what you are looking for and, rent (Or borrow) a few brands. Conduct your own listening test and, choose what sounds best to you.

Best Regards,
Title: Re: Sound Is Subjective
Post by: Garry Anderson on February 05, 2008, 03:44:56 pm
"Real torodial transformers..... !"

Lets go back to the 'good-ol-days' of quasi-complimentry NPN output stages, massive EI transformers and 300W at 1% distortion.
Nothing has sounded the same since those days.
I'm sure these manufacturers only develop new technologies to make us buy new amps.... Laughing
Title: Re: Sound Is Subjective
Post by: Richard Rajchel on February 05, 2008, 04:11:16 pm
These arguments are so ridiculous it's not even funny anymore. Arguing which amp sounds better and why is like arguing what shade of blue the sky is at 6pm just after a rain storm. It's so subjective, that there is no answer. More power? Sure, you think it should be louder, but the fact that our ears hear different frequencies at different "loudness" levels even if the measured SPL is the same confuses things even more. 130 dB at 80Hz will make a pile of rumble and may or may not sound loud, but 130 dB at 8000Hz will make most people run for their lives in pain. There is certainly a log rhythmic increase of cost for improvement in sound quality. The difference between a $700 Mackie mixer and a $1500 Soundcraft or A&H mixer might be quite noticeable to many people. The difference in sound quality between a $15000 Midas and a $100,000 mixer not 1 in 1000 people would be able to tell which is which in a blind audio test. Once you get to a certain point there's probably a .00001 % of the worlds population that can even tell the difference. The differences in amplifiers is probably much much less than that even....simply because there's only so much to an amplifier. A mixer is much more complicated and more components can have an effect on the sound. I would bet $1000 that if you took 100 engineers and setup an A/B blind comparison between a low end QSC amp and a Crown iTech and matched the voltage output of them both that the results would be 99% random. Sound is as subjective as beauty, or color, or political opinions. Someone will think it sounds incredible, and someone else might leave the show because the sound is so bad it's giving them a headache.

Name brand equipment is for people who have to fill riders, and to compare another subjective thing like customer service and reliability. The only people who know how reliable products actually are is the manufacturer that keeps track of repairs, and I'm guessing they don't share that information readily. I can find someone who's had 10 Behringer amps for the last 6 years running 5 nights a week without one failure, or someone with a Midas board that has to go in for repair at least 3-5 times a year.

Find tools that you are comfortable with and work the way you expect them to or are used to. You'll get the best sound you can that way. If you use an EQ with a constant Q of 1.5 and change to another brand that has something different and different circuitry it will react differently to what you are used to inputing for correcting that snare drum ring, or nasaly vocal tone, etc...

One last thing about "punchy" bass. What the heck does that mean in reality? Most people, including a lot of engineers think to get a great kick drum sound you need subs that go to 20Hz flat(OK I'm exaggerating a little), but that "kick in the chest" feeling is usually in the 60-80Hz range, and in all actuallity the first harmonic of 120-160Hz is where most of that feel comes from. you can EQ the crap out of a kick to get it to feel where ever you want I suppose, and kick drums obviously get tuned different and can be as big as a house or smaller than most floor toms, but this dream that you need to go super low to feel the kick in a live sound application is just flat out a lie. Compressed recordings are a completely different animal, so if you're a DJ don't listen to me...heh.
Title: Re: Sound Is Subjective
Post by: Scott Smith on February 05, 2008, 04:11:43 pm
In no way did I intend to start a DF discussion.  Is the mention of "slew rates" a thing of the past as well?  
Title: Re: Sound Is Subjective
Post by: Bennett Prescott on February 05, 2008, 04:43:25 pm
Scott Smith wrote on Tue, 05 February 2008 16:11

Is the mention of "slew rates" a thing of the past as well?

Yes. No modern amp should have any issue with slew rate limiting within the audible bandwidth.
Title: Re: Sound Is Subjective
Post by: Chuck Fry on February 05, 2008, 05:05:28 pm
Bennett Prescott wrote on Tue, 05 February 2008 13:43

Scott Smith wrote on Tue, 05 February 2008 16:11

Is the mention of "slew rates" a thing of the past as well?

Yes. No modern amp should have any issue with slew rate limiting within the audible bandwidth.


And especially not when driving subs!  Rolling Eyes
Title: Re: Sound Is Subjective
Post by: Greg Cameron on February 05, 2008, 05:13:04 pm
Richard Rajchel wrote on Tue, 05 February 2008 13:11

Arguing which amp sounds better and why is like arguing what shade of blue the sky is at 6pm just after a rain storm. It's so subjective, that there is no answer.


Yes and no. As has been stated many times here, not all amps behave the same when operated towards their limits. Different amp designs of similar power ratings will yield some performance difference with different boxes. There are differences and sometimes they're more then slightly noticeable.

Richard Rajchel wrote on Tue, 05 February 2008 13:11

The differences in amplifiers is probably much much less than that even....simply because there's only so much to an amplifier. A mixer is much more complicated and more components can have an effect on the sound. I would bet $1000 that if you took 100 engineers and setup an A/B blind comparison between a low end QSC amp and a Crown iTech and matched the voltage output of them both that the results would be 99% random. S


That's debatable. Sure, amps will probably sound the same - until they're pushed. And let's face it, most amps are pushed till they're nearly clipping at some point. Some will behave better then others. That's not subjective.

Richard Rajchel wrote on Tue, 05 February 2008 13:11

Name brand equipment is for people who have to fill riders, and to compare another subjective thing like customer service and reliability. The only people who know how reliable products actually are is the manufacturer that keeps track of repairs, and I'm guessing they don't share that information readily. I can find someone who's had 10 Behringer amps for the last 6 years running 5 nights a week without one failure, or someone with a Midas board that has to go in for repair at least 3-5 times a year.


While reliability is one factor in spec'ing gear, there are other tangible reason to go with using top shelf gear. If your statement was true, then a Behringer rig would perform up there at a fraction of the cost of L'Acoustics rig with a Midas board. Ain't gonna happen. Not so long ago, Behringer was consider shit for reliability and sound, so bargain basement is often not such a bargain.

Richard Rajchel wrote on Tue, 05 February 2008 13:11


One last thing about "punchy" bass. What the heck does that mean in reality? Most people, including a lot of engineers think to get a great kick drum sound you need subs that go to 20Hz flat(OK I'm exaggerating a little), but that "kick in the chest" feeling is usually in the 60-80Hz range, and in all actuallity the first harmonic of 120-160Hz is where most of that feel comes from. you can EQ the crap out of a kick to get it to feel where ever you want I suppose, and kick drums obviously get tuned different and can be as big as a house or smaller than most floor toms, but this dream that you need to go super low to feel the kick in a live sound application is just flat out a lie. Compressed recordings are a completely different animal, so if you're a DJ don't listen to me...heh.


If you've have an opportunity to mix on a rig that is truly capable of reproducing infrasonics below 30 Hz, you would see that there can be a significant impact on the quality of the performance compared to a similar rig which can't do much below even 40Hz. That's no lie...

Greg

Title: Re: Sound Is Subjective
Post by: Garry Anderson on February 05, 2008, 05:13:47 pm
Thanks Richard for your informed reply, I've been trying to convince people along these lines without any result. Even offering explanations of why there are audible results have fallen on "deaf ears".

The only conclusion I have made from these discussions is that most people who frequent these ones are fixed in their ideas and don't won't to be admit to being mistaken or un-informed.
Title: Re: Sound Is Subjective
Post by: Richard Rajchel on February 05, 2008, 05:28:02 pm
I'm not sure how well informed I might be, but the biggest impact on live sound is the talent of the musicians. The second biggest is probably the talent of the person mixing the band. As long as there's enough power to get the vocals over the sound of the band anyone should be able to get a listen-to-able mix.

Infrasonics? Sounds like snake oil to me. So does the infrared contend of the pigments used to paint the Mona Lisa have an effect on what we perceive as art? "The term infrasonics refers to waves of a frequency below the range of human hearing" That's a quote from Encyclopedia Britannica. If you can't hear it is it effecting what you do actually hear? If the actual wave is strong enough you could likely feel it, but not hear it. Can you see ultraviolet light, or infrared light waves? Hogwash, nonsense, etc...

It's all perception. If you think infrasonics enhance a live performance then for you it probably does...just knowing they are there I guess does it for you. The other 2,500 people at the show don't have a clue. The ground might be rumbling a bit below audible frequencies, but this isn't sound anymore if it can't be heard...more like a miniature earthquake. That being said, vibrations like that can enhance anything where males and females are present at the same time and alcohol is involved...heh.

I only used Behringer as an example because they get bashed on the most. I have no facts...it was just an illustrative example.
Title: Re: Sound Is Subjective
Post by: Bob Leonard on February 05, 2008, 06:16:30 pm
Richard Rajchel wrote on Tue, 05 February 2008 16:11



One last thing about "punchy" bass. What the heck does that mean in reality? Most people, including a lot of engineers think to get a great kick drum sound you need subs that go to 20Hz flat(OK I'm exaggerating a little), but that "kick in the chest" feeling is usually in the 60-80Hz range, and in all actuallity the first harmonic of 120-160Hz is where most of that feel comes from. you can EQ the crap out of a kick to get it to feel where ever you want I suppose, and kick drums obviously get tuned different and can be as big as a house or smaller than most floor toms, but this dream that you need to go super low to feel the kick in a live sound application is just flat out a lie. Compressed recordings are a completely different animal, so if you're a DJ don't listen to me...heh.


To this I agree. For me QSC 3602s dont get it for low frequency use below 100hz. Mine shut down under low voltage conditions, generate tremendous amounts of heat and my subs don't respond as well as they do using QSC 4050HDs. I'm not going to perform any analysis to prove my point to myself or anyone else. The 4050 has more in reserve than the 3602 and runs better under less than perfect conditions even though the specs are almost identical. However, if I roll the specs up and put the specs for the 4050 in one ear and the the specs for the 3602 in the other I don't hear any difference. But, when I pull that paper out of my ears and listen to them side by side the difference is night and day. Shocked To be kind though, the 3602 is a perfect amp (IMO) for a JBL SRX725 (with that extra 15" speaker helping to reproduce the in the 100-160hz range.)

I read the statement linear in a response. By default power amplifiers are all linear. The job of a power amplifier used for radio, sound, etc. is to faithfully reproduce the input signal at an amplified (larger) level, be it 10, 100, 1000 times larger or more. I tend to think that class of service is what the post was meant to state, examples below as applied to ham radio. The same applies to audio;

The class A amplifiers are very inefficient, they can never have an efficiency better than 50%. The semiconductor or valve conducts throughout the entire RF cycle. The mean anode current for a valve should be set to the middle of the linear section of the curve of the anode current vs grid bias potential.

Class B amplifiers are more efficient, they can be 60 to 65% efficient. The semiconductor or vacuum tube conducts through half the RF cycle.

Class AB1 is where the grid is more negatively biased than it is in class A.

Class AB2 is where the grid is often more negatively biased than in AB1, also the size of the input signal is often larger. When the drive is able to make the grid become positive the grid current will increase.

In a class B amplifier the grid current drawn will be large, and a large drive power will be required.

Class C amplifiers are still more efficient, they can be about 75% efficient with a conduction range of about 120o but they are very non linear. They can only be used for FM or CW use only. The semiconductor or valve conducts through less than half the RF cycle. The increase in efficiency can allow a given valve to deliver more RF power than it could do so in class A or AB. For instance two 4CX250B tetrodes operating at 144 MHz can deliver 400 watts in class A, but when biased into class C they can deliver 1000 watts without fear of overheating. Even more grid current will be needed.

A side effect of improving the efficiency is that the current drawn from the high voltage supply will vary more as a function of the power input into the amplifier, this can result in unwanted effects such as the output of the HT pack being modulated by the audio modulated RF driven into the amplifier.
Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 05, 2008, 06:31:30 pm
Scott Smith wrote on Tue, 05 February 2008 15:11

In no way did I intend to start a DF discussion.  Is the mention of "slew rates" a thing of the past as well?  


Yes.. bingo, ding ding ding...

Long ago in a far away time, amplifiers were made with vacuum tubes and had much higher output impedances. In those days DF was audible (and some tube aficionados actually prefer it low).

In the early days of solid state the power devices were slow and not very robust. They often had less slew rate than needed to deliver a full 20 kHz power bandwidth.

Modern solid state amps have had adequately low source impedance and adequately fast enough slew rate, to not be an issue, for decades.

IMO the useful differences these days are in amplifier efficiency (class D or multi rail G/H) and power supply features like regulation and PFC. There are a few other clever combinations of trick tracking power supplies and such that improve overall efficiency.

The rest is attention to detail, cheap designs are cheap generally because they lack "features" of more expensive designs from the same manufacturer. Sometimes these features are subtle and not obvious but you rarely get more than you pay for and sometimes less.

JR
Title: Re: Sound Is Subjective
Post by: Andy Peters on February 05, 2008, 06:39:18 pm
Richard Rajchel wrote on Tue, 05 February 2008 14:11

One last thing about "punchy" bass. What the heck does that mean in reality? Most people, including a lot of engineers think to get a great kick drum sound you need subs that go to 20Hz flat(OK I'm exaggerating a little), but that "kick in the chest" feeling is usually in the 60-80Hz range, and in all actuallity the first harmonic of 120-160Hz is where most of that feel comes from.


Agreed. And furthermore, from which cabinet do you get that 160 Hz?

Answer: not the sub!

-a
Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 05, 2008, 06:44:43 pm
Bob Leonard wrote on Tue, 05 February 2008 17:16

Richard Rajchel wrote on Tue, 05 February 2008 16:11



One last thing about "punchy" bass. What the heck does that mean in reality? Most people, including a lot of engineers think to get a great kick drum sound you need subs that go to 20Hz flat(OK I'm exaggerating a little), but that "kick in the chest" feeling is usually in the 60-80Hz range, and in all actuallity the first harmonic of 120-160Hz is where most of that feel comes from. you can EQ the crap out of a kick to get it to feel where ever you want I suppose, and kick drums obviously get tuned different and can be as big as a house or smaller than most floor toms, but this dream that you need to go super low to feel the kick in a live sound application is just flat out a lie. Compressed recordings are a completely different animal, so if you're a DJ don't listen to me...heh.


To this I agree. For me QSC 3602s dont get it for low frequency use below 100hz. Mine shut down under low voltage conditions, generate tremendous amounts of heat and my subs don't respond as well as they do using QSC 4050HDs. I'm not going to perform any analysis to prove my point to myself or anyone else. The 4050 has more in reserve than the 3602 and runs better under less than perfect conditions even though the specs are almost identical. However, if I roll the specs up and put the specs for the 4050 in one ear and the the specs for the 3602 in the other I don't hear any difference. But, when I pull that paper out of my ears and listen to them side by side the difference is night and day. Shocked To be kind though, the 3602 is a perfect amp (IMO) for a JBL SRX725 (with that extra 15" speaker helping to reproduce the in the 100-160hz range.)

I read the statement linear in a response. By default power amplifiers are all linear. The job of a power amplifier used for radio, sound, etc. is to faithfully reproduce the input signal at an amplified (larger) level, be it 10, 100, 1000 times larger or more. I tend to think that class of service is what the post was meant to state, examples below as applied to ham radio. The same applies to audio;

The class A amplifiers are very inefficient, they can never have an efficiency better than 50%. The semiconductor or valve conducts throughout the entire RF cycle. The mean anode current for a valve should be set to the middle of the linear section of the curve of the anode current vs grid bias potential.

Class B amplifiers are more efficient, they can be 60 to 65% efficient. The semiconductor or vacuum tube conducts through half the RF cycle.

Class AB1 is where the grid is more negatively biased than it is in class A.

Class AB2 is where the grid is often more negatively biased than in AB1, also the size of the input signal is often larger. When the drive is able to make the grid become positive the grid current will increase.

In a class B amplifier the grid current drawn will be large, and a large drive power will be required.

Class C amplifiers are still more efficient, they can be about 75% efficient with a conduction range of about 120o but they are very non linear. They can only be used for FM or CW use only. The semiconductor or valve conducts through less than half the RF cycle. The increase in efficiency can allow a given valve to deliver more RF power than it could do so in class A or AB. For instance two 4CX250B tetrodes operating at 144 MHz can deliver 400 watts in class A, but when biased into class C they can deliver 1000 watts without fear of overheating. Even more grid current will be needed.

A side effect of improving the efficiency is that the current drawn from the high voltage supply will vary more as a function of the power input into the amplifier, this can result in unwanted effects such as the output of the HT pack being modulated by the audio modulated RF driven into the amplifier.



Before everybody starts looking for class C audio amplifiers be advised that it is a "RF only" design topology that relies upon some resonant circuits. And FM or CW only, doesn't mean Country Western or FM easy listening.. it means constant sine waves.

TMI....

JR

Title: Re: Sound Is Subjective
Post by: Chuck Fry on February 05, 2008, 07:04:26 pm
Hmmm... resonant circuits... could a Class C power amp be useful for those "one-note" car audio subs you hear booming down the road?  Laughing
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Tim Duffin on February 05, 2008, 07:18:01 pm
Kenwood actually produced an amplifier with a parallel servo circuit in line with the last output device which had as its only function, to increase the damping factor above 10,000.  Unfortunately this connection was optional and most people didn't hook it up because they didn't like the way it "sounded" Laughing with all that extra damping.  


T
Title: Re: Sound Is Subjective
Post by: Scott Smith on February 05, 2008, 07:19:08 pm
Well, putting DF, slew rates, and old school issues aside, has anybody offered any technical reasons why amps sound different, or is it just mind over matter?
Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 05, 2008, 07:22:32 pm
perhaps

JR
Title: Re: Sound Is Subjective
Post by: Tim Duffin on February 05, 2008, 07:28:46 pm
Bob Leonard wrote on Tue, 05 February 2008 15:16

Richard Rajchel wrote on Tue, 05 February 2008 16:11



One last thing about "punchy" bass. What the heck does that mean in reality? Most people, including a lot of engineers think to get a great kick drum sound you need subs that go to 20Hz flat(OK I'm exaggerating a little), but that "kick in the chest" feeling is usually in the 60-80Hz range, and in all actuallity the first harmonic of 120-160Hz is where most of that feel comes from. you can EQ the crap out of a kick to get it to feel where ever you want I suppose, and kick drums obviously get tuned different and can be as big as a house or smaller than most floor toms, but this dream that you need to go super low to feel the kick in a live sound application is just flat out a lie. Compressed recordings are a completely different animal, so if you're a DJ don't listen to me...heh.


To this I agree. For me QSC 3602s dont get it for low frequency use below 100hz. Mine shut down under low voltage conditions, generate tremendous amounts of heat and my subs don't respond as well as they do using QSC 4050HDs. I'm not going to perform any analysis to prove my point to myself or anyone else. The 4050 has more in reserve than the 3602 and runs better under less than perfect conditions even though the specs are almost identical. However, if I roll the specs up and put the specs for the 4050 in one ear and the the specs for the 3602 in the other I don't hear any difference. But, when I pull that paper out of my ears and listen to them side by side the difference is night and day. Shocked To be kind though, the 3602 is a perfect amp (IMO) for a JBL SRX725 (with that extra 15" speaker helping to reproduce the in the 100-160hz range.)

I read the statement linear in a response. By default power amplifiers are all linear. The job of a power amplifier used for radio, sound, etc. is to faithfully reproduce the input signal at an amplified (larger) level, be it 10, 100, 1000 times larger or more. I tend to think that class of service is what the post was meant to state, examples below as applied to ham radio. The same applies to audio;

The class A amplifiers are very inefficient, they can never have an efficiency better than 50%. The semiconductor or valve conducts throughout the entire RF cycle. The mean anode current for a valve should be set to the middle of the linear section of the curve of the anode current vs grid bias potential.

Class B amplifiers are more efficient, they can be 60 to 65% efficient. The semiconductor or vacuum tube conducts through half the RF cycle.

Class AB1 is where the grid is more negatively biased than it is in class A.

Class AB2 is where the grid is often more negatively biased than in AB1, also the size of the input signal is often larger. When the drive is able to make the grid become positive the grid current will increase.

In a class B amplifier the grid current drawn will be large, and a large drive power will be required.

Class C amplifiers are still more efficient, they can be about 75% efficient with a conduction range of about 120o but they are very non linear. They can only be used for FM or CW use only. The semiconductor or valve conducts through less than half the RF cycle. The increase in efficiency can allow a given valve to deliver more RF power than it could do so in class A or AB. For instance two 4CX250B tetrodes operating at 144 MHz can deliver 400 watts in class A, but when biased into class C they can deliver 1000 watts without fear of overheating. Even more grid current will be needed.

A side effect of improving the efficiency is that the current drawn from the high voltage supply will vary more as a function of the power input into the amplifier, this can result in unwanted effects such as the output of the HT pack being modulated by the audio modulated RF driven into the amplifier.




I assume you know that this quotation (even though it is full of horrible, oversimplified, bordering on completely wrong information) is for TUBE amplifiers, right?  I will forgive you if you can name the electronic circuit which uses a class C amplifier.  Twisted Evil  

BTW-- FACT: class A amplifiers are maximum 25% efficient.


T


Title: Re: Sound Is Subjective
Post by: Richard Rajchel on February 05, 2008, 07:34:25 pm
Could it be that the amps these days are just being built closer to the "edge" of acceptable sound. Yesteryears 1000 watt amp was so over-built that it could probably take a nasty 5000 watt spike or more and not even sweat. Todays amps based on ICs and switching power supplies just simply don't have as much in reserve. Sure a Class H or whatever powered amplifier can chug along at 90% efficiency, but when the voltage sags it just can't keep up. That old 100 pound/1000 watt amp had capacitors the size of a house and matching transformers and heat sinks too probably. I would guess that if input voltage, current, etc... was kept constant that todays amps could easily compare to older ones. In the real world however power sags/spikes are as common as groupies at a heavy metal concert.
Title: Re: Sound Is Subjective
Post by: SteveKirby on February 05, 2008, 08:35:29 pm
Chuck Fry wrote on Tue, 05 February 2008 18:04

Hmmm... resonant circuits... could a Class C power amp be useful for those "one-note" car audio subs you hear booming down the road?  Laughing

Many years ago I worked with a guy who got a patented on a video sweep amplifier that fed the deflection coil's back emf from the flyback into storage for the next sweep.  Huge increase in efficiency.  I asked him about car sub amps as those guys want all the output for a given input current that they can get, regardless of quality.  He'd have owned the market.  He felt that car audio was beneath his dignity as an engineer.  Too low in frequency to be high tech enough for him.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Garry Anderson on February 06, 2008, 02:34:31 am
In a previous thread I offered several technical explanations on why different amps with similar specs would sound different driving a system..... and was basically ignored.

My conclusion is it all comes down to "I bought this amp so it's better than yours..." syndrome.

I'm not going to waste my time typing it all again because all that will happen is that another thread will start up again next week....I bought a Crown DC300A last week and it has a much better bass than my old Lab FQ10000.... Sad
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Keagan Corcoran on February 06, 2008, 07:11:24 am
This seems to have gone off topic.... my respone to the original post.

Alexander B Larsson wrote on Tue, 05 February 2008 10:11

I am still searching for that "big amp" for the bass boxes, but the more I read, the more contradictory the information seems...
I currently run a number of older "conventional PSU" Labgruppen amps, but having one bridged amp per driver is HEAVY!  Confused

(Finding amps for listening tests is somewhat hard in Sweden, as many of the MI shops carry only entry level stuff, like Phonic, Alesis etc.)

Normally one can find some general trends in opininons/reviews of stuff, but amps seem different? Strange, since they should actually have the smallest impact on overall fidelity of the rig, from a distorsion point of view.

Some praise the QSC RMX 4050 and 5050 for subs, while some claim their upgrade from RMX to some "switched" Crown, Lab or similar made a world of difference. Listening test (shootout) says the differences are small, but that test only included few speakers, etc...

Considering our ear's limited sensitivity to detect distorsion in the bass range, what IS it that we hear?

A guy I talked to described the lightweight Lab amps as "punchy" in the bass, but are we talking about that amp adding something that was not originally there? Or are many other amps missing the "punch", whatever that would be?

Power is clearly important, but amps that run below their clipping point should not colour sound at all, at least not detectable...

/Alexander


You have a NUMBER of CONVENTIONAL PS LABS??? And you are winging?? If they are too heavy SUCK IT UP  Laughing . You only have to lift them twice per gig is my take on it.

For my money, the reason labs and camco's get great raps is because they can do with switchmode what others can barely do with iron.

The reason that 'old' or heavy amps sound better for subs is because (very basically) there is more power in the reserve at any given time for the speaker to draw on for peaks etc. Sure all drivers draw on supplies extra for peaks, but subs REALLY draw for peaks so there needs to be more in the power reserve. (sorry if this was patronising, i didnt know if this is what you were asking.)

And yes sound differences are small. I have run rigs on all toroidal amps and rigs on all switchmode. It really doesnt matter until you get into the big games, but in my view anyone can buy gear, it is the small things that make the rig. Go to the gym more.

Title: Re: Sound Is Subjective
Post by: Gene Hardage on February 06, 2008, 07:13:39 am
Richard Rajchel wrote on Tue, 05 February 2008 17:28

I'm not sure how well informed I might be, but the biggest impact on live sound is the talent of the musicians. The second biggest is probably the talent of the person mixing the band. As long as there's enough power to get the vocals over the sound of the band anyone should be able to get a listen-to-able mix......



YES and YES
The magic happens when the musicians and the sound person are on the same page and make an effort to stay within the limitations of the system and the room it's in.


Wish I could offer an answer to the original poster question.  I've always had to make do with whatever was in house or use my own limited resourses.
Title: Re: Sound Is Subjective
Post by: Don Boomer on February 06, 2008, 09:45:05 am
Scott Smith wrote on Tue, 05 February 2008 18:19

has anybody offered any technical reasons why amps sound different


Yes ... as JR said amps sound different when  in the non linear mode.  What you are "hearing" is the amp clipping or limiting or running out of power supply, etc.

An amp should have no "sound" ... good or bad if we use the old standard ...striaght wire with gain.

I think the way that amps are used today they do have a "sound".  It is typical to see amps driven into the non linear mode.  In fact I think it has become commonplace.  That makes a smaller system sound "louder".  

WRT amps for subs I think a lot of listeners actually prefer some distortion in the system ... it "sounds better".  I'm fine with that I just think you have to define your standard when talking about amplifier "sound"

I don't think that the first practitioners of electric guitar were looking to sound like anything but an acoustic guitar only louder but look what it's turned into. I won't even start with mp3's. [ /bad analogy]

Seems like folks are out there selecting their power amps for "tone control"
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Bob Leonard on February 06, 2008, 10:02:20 am
Yes Tim, I am aware those are all tube circuits, and;

A class C amplifier is biased beyond cutoff. The class C amplifier like the class B amplifier will draw no current with no signal input but a class B will start to draw current as soon as a signal is applied and a class C will only start to draw current when the signal strength is sufficient to go beyond the bias level. The class C amplifier is not linear but is the highest in efficiency.

In all classes of amplifier the linearity of the amplifier is determined by it's class.

The APS-20 radar on an EC-121 Willy Victor used a class "C" amplifier. RTTY, CW are often used with class "C" amplifiers, but they can not be used with SSB.

I posted these as classic examples, and being as basic as these classes of amplifier are I would think it may be good reading material for people who may want to understand amplifiers and how they operate. Guitar players may find interest in class A/B amplifier circuits especially if they use a Fender amplifier.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Tim McCulloch on February 06, 2008, 10:58:18 am
Another senseless "flat view" reply tragedy...

Bob, who the fuck are you replying to?

With love,

The not as old soundman.... Wink
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: John Roberts {JR} on February 06, 2008, 11:33:31 am
Bob Leonard wrote on Wed, 06 February 2008 09:02

Yes Tim, I am aware those are all tube circuits, and;

A class C amplifier is biased beyond cutoff. The class C amplifier like the class B amplifier will draw no current with no signal input but a class B will start to draw current as soon as a signal is applied and a class C will only start to draw current when the signal strength is sufficient to go beyond the bias level. The class C amplifier is not linear but is the highest in efficiency.

In all classes of amplifier the linearity of the amplifier is determined by it's class.

The APS-20 radar on an EC-121 Willy Victor used a class "C" amplifier. RTTY, CW are often used with class "C" amplifiers, but they can not be used with SSB.

I posted these as classic examples, and being as basic as these classes of amplifier are I would think it may be good reading material for people who may want to understand amplifiers and how they operate. Guitar players may find interest in class A/B amplifier circuits especially if they use a Fender amplifier.


I invite people to ignore any discussion of class C as it doesn't apply to audio amps, and rebuttal intended to inflame rather than illuminate. For a (very) basic overview here's a link to piece I wrote years ago while at my old gig.

http://www.peavey.com/support/technotes/poweramps/classact.c fm

Looking at the amps touted on page two you can date how old the white paper is, but the discussion is a good starting point for any wanting to understand amplifier classes.

JR
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Andy Peters on February 06, 2008, 01:08:14 pm
Bob Leonard wrote on Wed, 06 February 2008 08:02

Yes Tim, I am aware those are all tube circuits, and;

A class C amplifier is biased beyond cutoff. The class C amplifier like the class B amplifier will draw no current with no signal input but a class B will start to draw current as soon as a signal is applied and a class C will only start to draw current when the signal strength is sufficient to go beyond the bias level. The class C amplifier is not linear but is the highest in efficiency.

In all classes of amplifier the linearity of the amplifier is determined by it's class.

The APS-20 radar on an EC-121 Willy Victor used a class "C" amplifier. RTTY, CW are often used with class "C" amplifiers, but they can not be used with SSB.


As The Good Tim says, flat view, anyone? USE THE QUOTE BUTTON.

And how is this relevant to the topic at hand? Other than to get into another mudwrestle with Duffin?

Quote:

I posted these as classic examples, and being as basic as these classes of amplifier are I would think it may be good reading material for people who may want to understand amplifiers and how they operate. Guitar players may find interest in class A/B amplifier circuits especially if they use a Fender amplifier.


And the design goals of a guitar amplifier are at cross purposes with one designed for sound reproduction.

One is a tone generator, one is not.

So the discussion is rather pointless.

-a
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Silas Pradetto on February 06, 2008, 03:35:36 pm
Damping factor is the load impedance divided by the output impedance of the amplifier. This means, with an 8 ohm load and a .01 ohm output impedance of the amplifier, you would have a damping factor of 800. Damping factor has quite a bit to do with bass quality. It is related to cone control such that a higher damping factor is more control. If there is more control, the woofer flaps around less and relies less on it's own suspension to return it to the "zero" point in it's travel, making everything sound "punchier." I hope that kind of made sense.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Andy Peters on February 06, 2008, 03:40:44 pm
Silas Pradetto wrote on Wed, 06 February 2008 13:35

Damping factor is the load impedance divided by the output impedance of the amplifier. This means, with an 8 ohm load and a .01 ohm output impedance of the amplifier, you would have a damping factor of 800. Damping factor has quite a bit to do with bass quality. It is related to cone control such that a higher damping factor is more control. If there is more control, the woofer flaps around less and relies less on it's own suspension to return it to the "zero" point in it's travel, making everything sound "punchier." I hope that kind of made sense.


You forget the salient point: overall damping factor is severely degraded by the cable between the amp and the driver, as that cable's resistance adds to the amp output impedance.

In fact, the cable resistance essentially sets the damping factor, making amplifier damping factor irrelevant except maybe as a marketing bullet point.

This horse is dead.

Please stop beating it.

-a
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Bennett Prescott on February 06, 2008, 03:43:29 pm
Oy.

Here's another article that I wrote because of frustration from the last time this came up.

http://www.bennettprescott.com/downloads/dampingfactor.pdf
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Bob Leonard on February 06, 2008, 03:52:02 pm
Andy Peters wrote on Wed, 06 February 2008 13:08

Bob Leonard wrote on Wed, 06 February 2008 08:02

Yes Tim, I am aware those are all tube circuits, and;

A class C amplifier is biased beyond cutoff. The class C amplifier like the class B amplifier will draw no current with no signal input but a class B will start to draw current as soon as a signal is applied and a class C will only start to draw current when the signal strength is sufficient to go beyond the bias level. The class C amplifier is not linear but is the highest in efficiency.

In all classes of amplifier the linearity of the amplifier is determined by it's class.

The APS-20 radar on an EC-121 Willy Victor used a class "C" amplifier. RTTY, CW are often used with class "C" amplifiers, but they can not be used with SSB.


As The Good Tim says, flat view, anyone? USE THE QUOTE BUTTON.

And how is this relevant to the topic at hand? Other than to get into another mudwrestle with Duffin?

Quote:

I posted these as classic examples, and being as basic as these classes of amplifier are I would think it may be good reading material for people who may want to understand amplifiers and how they operate. Guitar players may find interest in class A/B amplifier circuits especially if they use a Fender amplifier.


And the design goals of a guitar amplifier are at cross purposes with one designed for sound reproduction.

One is a tone generator, one is not.

So the discussion is rather pointless.

-a


Andy,
I don't care about Duffin. He asked for an answer and got it. And since when are class A/B amplifiers not a part of sound reproduction. I seem to remember working with many prior to the use of transistors in amplifier output stages. I don't remember saying anything about preamplifier circuits at all. Maybe that's where your confused. Besides that the above were used as examples of amplifier class in response to someone who doesn't understand the meaning of the word linear. Ever read an RCA tube manual? Regardless of the class most amplifiers can trace their roots back to those simplistic amplifiers of days gone by in some way or another.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: John Roberts {JR} on February 06, 2008, 04:42:16 pm
Silas Pradetto wrote on Wed, 06 February 2008 14:35

." I hope that kind of made sense.


No... it doesn't.

DF has been well discussed here, again, and again, and again...

JR
Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 07, 2008, 12:27:05 am
Quote:


I think the way that amps are used today they do have a "sound".  It is typical to see amps driven into the non linear mode.  In fact I think it has become commonplace.  That makes a smaller system sound "louder".  



http://www.moultonlabs.com/more/power_amps_revisited/
Title: Re: Sound Is Subjective
Post by: Andy Peters on February 07, 2008, 01:24:43 am
Ted Olausson wrote on Wed, 06 February 2008 22:27

Quote:


I think the way that amps are used today they do have a "sound".  It is typical to see amps driven into the non linear mode.  In fact I think it has become commonplace.  That makes a smaller system sound "louder".  



http://www.moultonlabs.com/more/power_amps_revisited/


Well, he's driving easier loads at lower SPLs than typical for SR use and it's obvious that driving the amps to the edge all night is not a requirement.

But, really, it just sounds like the guy who built the amps conservatively rated them lower than what they can really do. Which is fine, and even laudable, especially considering that he leaves some "marketing watts" on the table.

Note how they measure SPL, but not amplifier output power, which would be the better test.

-a
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Bob Lee (QSC) on February 07, 2008, 01:26:49 pm
Duncan McLennan wrote on Tue, 05 February 2008 08:22

linear power supplies.


I suppose a battery could be a linear power supply.

An AC-to-DC power supply, whether switch-mode or conventional, is almost always non-linear.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Bob Lee (QSC) on February 07, 2008, 01:29:29 pm
The RMX5050, 8001, and 10001 all have conventional (mains frequency) power supplies, not linear ones.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Chuck Fry on February 07, 2008, 01:43:01 pm
I found this "smackdown" thread via a link from a DIYaudio.com thread:

http://srforums.prosoundweb.com/index.php/m/229083/19784/

Now what would explain the lower power output at low frequencies of 3 of the 4 amps tested? The PLX 3402 puts out literally twice the power at 20 KHz that it does at 20 Hz. Even the Crest 9001 has a dip in the power curve at 50 and 200 Hz - in the heart of subwoofer country. The burst test should be pulling the same energy from the power supply irrespective of frequency, shouldn't it?

Answer that question and maybe we'll have a clue what we're really hearing from amps on sub duty.

(BTW this is not intended as bashing any particular amp maker - I happen to own a PLX 3402 and have been happy with it as part of a bass guitar rig.)
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: John Roberts {JR} on February 07, 2008, 02:08:04 pm
Chuck Fry wrote on Thu, 07 February 2008 12:43

I found this "smackdown" thread via a link from a DIYaudio.com thread:

http://srforums.prosoundweb.com/index.php/m/229083/19784/

Now what would explain the lower power output at low frequencies of 3 of the 4 amps tested? The PLX 3402 puts out literally twice the power at 20 KHz that it does at 20 Hz. Even the Crest 9001 has a dip in the power curve at 50 and 200 Hz - in the heart of subwoofer country. The burst test should be pulling the same energy from the power supply irrespective of frequency, shouldn't it?

Answer that question and maybe we'll have a clue what we're really hearing from amps on sub duty.

(BTW this is not intended as bashing any particular amp maker - I happen to own a PLX 3402 and have been happy with it as part of a bass guitar rig.)


While I am not familiar with than particular amp, the general mechanism that explains why an amplifier has lower power output at 20 Hz than 20kHz has been well described here several times.

The PS capacitors in conventional PS are charged at a rep rate of 2x mains frequency (100 or 120Hz). Pure tones much higher than that charging rep rate pull roughly half the time from the + supply and half the time from the - supply. Pure tones that are much lower than the charging rep rate appear to alternately pull from one supply for several charging cycles, then from the other. This results in an effective 2:1 difference in short term PS draw.

Max power is defined by clipping, which in these cases is limited by the bottom of the ripple voltage trough. Depending on how the PS caps are sized it's easy to see a measurable difference between frequency extremes.

For LF applications, amplifiers should be specified based on their rated LF output. If that's still confusing, I can't help you.

Note: real world waveforms are rarely pure tones, but in a narrow band sub application the "one or the other" PS draw phenomenon occurs. It's also worth note, bridging draws from both supplies all the time and will deliver slightly more power output than dual mono...   Now please lets not bring that up again too...... A dB here or there will not make a huge difference, except on paper.

JR

Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Chuck Fry on February 07, 2008, 02:33:57 pm
John Roberts  {JR} wrote on Thu, 07 February 2008 11:08

While I am not familiar with than particular amp, the general mechanism that explains why an amplifier has lower power output at 20 Hz than 20kHz has been well described here several times.

The PS capacitors in conventional PS are charged at a rep rate of 2x mains frequency (100 or 120Hz). Pure tones much higher than that charging rep rate pull roughly half the time from the + supply and half the time from the - supply. Pure tones that are much lower than the charging rep rate appear to alternately pull from one supply for several charging cycles, then from the other. This results in an effective 2:1 difference in short term PS draw.



In the referenced test, the PLX is driving a 4 ohm load bridged. This loads both power supply rails equally. So I don't quite understand how your description explains the test results. I could see that the peaks of the 20 Hz tone appear as a continuous load on the power supply where the higher tones are seen as a lesser load.

I should probably ping you and Bob Lee offline to try and puzzle this out.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Bob Lee (QSC) on February 07, 2008, 03:35:48 pm
Alexander B Larsson wrote on Tue, 05 February 2008 10:46

And that amps that on paper are indistinguishable still do not sound the same, even within their linear operation (as in no clipping/current limiting).


Among the biggest problems are that when we compare amps …



Yes, you can take two amps that are indistinguishable on paper, even two of the same model, and they'll sound different if they're set to different gains.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Pascal Pincosy on February 07, 2008, 05:05:36 pm
Bob Lee (QSC) wrote on Thu, 07 February 2008 12:35

Among the biggest problems are that when we compare amps …

  • they're seldom compared side-by-side.
  • they're seldom compared with gains matched--i.e., at the same SPL from one to another.
  • they're seldom compared blind--i.e., without knowing which one we're listening to.



I did an amp shootout a few months ago where we did all of the above properly. The results? Entirely inconclusive. Buy amps based on price, feature-set, weight, and brand rep. Don't bother trying to find the best-sounding amp. Your results will change based on the source material used, the speakers used, and the phase of the moon.

http://srforums.prosoundweb.com/index.php/t/27380/9721/

PS I am, however, in full support of Langston's smackdown testing and I'd like to see it reproduced for other amps on the market. If an amp puts out half its rated power at a frequency you're trying to reproduce, you're losing 3dB of output. That's a significant loss.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: SteveKirby on February 07, 2008, 05:10:58 pm
Pascal Pincosy wrote on Thu, 07 February 2008 16:05

Bob Lee (QSC) wrote on Thu, 07 February 2008 12:35

Among the biggest problems are that when we compare amps …

  • they're seldom compared side-by-side.
  • they're seldom compared with gains matched--i.e., at the same SPL from one to another.
  • they're seldom compared blind--i.e., without knowing which one we're listening to.



I did an amp shootout a few months ago where we did all of the above properly. The results? Entirely inconclusive. Buy amps based on price, feature-set, weight, and brand rep. Don't bother trying to find the best-sounding amp. Your results will change based on the source material used, the speakers used, and the phase of the moon.

http://srforums.prosoundweb.com/index.php/t/27380/9721/


That shootout did notice a subtle different when used for subs.  That actually helped me make my choice to get a Crest Pro9200, which has worked very well for me.  In spite of it being one of those new fangled switchers.  If we weren't on opposite coasts, it might be fun to compare it to Bob's big iron.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Pascal Pincosy on February 07, 2008, 05:23:26 pm
SteveKirby wrote on Thu, 07 February 2008 14:10

That shootout did notice a subtle different when used for subs.  That actually helped me make my choice to get a Crest Pro9200, which has worked very well for me.  In spite of it being one of those new fangled switchers.  If we weren't on opposite coasts, it might be fun to compare it to Bob's big iron.


Yes there were subtle differences, and they seemed to me to be entirely dependent on amplifier/loudspeaker combos and on source material. There was no one amp which sounded "best". One amp would sound good with a specific speaker, and not with another. And I gamed the participants enough to realize that an amp that was considered to sound "bad" at one point in the testing would end up sounding "good" a few minutes later.

Not to say that I didn't have certain personal preferences, but I certainly would take them with a grain of salt.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Steve Kunkle on February 07, 2008, 06:30:11 pm
I am in complete agreeance with Pascal. I have found that its all about application.  In my case, I run KF 650's over SB 528's.  I switched from Crown Macrotechs to QSC PL's(6.0 II's on subs, mids and high mids, 230 on highs).  I found that the highs sounded maybe a little crisper... maybe.  But for my application I do miss my 5002's on the subs.  In my case, they did sound better with my speakers, even they have a power rating a bit less than the 6.0.  I don't think thats enough to make me switch back, but if you are running subs of similar nature (something with the p300 driver) it may be something to consider.  In conclusion though, the best wisdome that has been shared in this thread has been to rent, borrow, or otherwise comandeer numerous amps to see which one pleases YOUR ear the most on YOUR RIG.  We are all our own toughest critics when it comes to our own systems, so if you can find what you like and are happy than you have won the battle.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Richard Rajchel on February 07, 2008, 06:32:20 pm
I couldn't agree more. Everyone likes to believe they have somewhat golden ears. When we all hear as much with our eyes and preconceived notions is closer to the truth. In blind tests with output matched and no "voltage" shutdowns etc... I doubt anyone could tell you which amp was a Lab and which one was an RMX. The results would be completely random. Aren't volts volts and amps just amps? There are most certainly nuances, and maybe one amp has a sag at a certain frequency, but with just about any two amps behind a curtain driving identical speakers with the identical program material at the identical voltage I can't imagine anyone could tell. Reliability, weight, and how an amp handles overloads or under powering would be far better criteria than how you think an amp might sound better than another.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: SteveKirby on February 07, 2008, 06:51:31 pm
Ah, the old straight wire with gain, all amps sound the same debate.

Someone mentioned it before, if two pieces of gear measure the same, but sound different, you're measuring the wrong thing.

It's kind of difficult to set up listening tests in SR since you need a source and venue and can't readily a/b things.  When I worked at Dolby, one of the golden ears there (had been asked to review various famous recordings for potential alterations among other things) told me that in his opinion given the compression drivers and horns in cinema or SR, the amps didn't make much difference.  But in a good home system or controlled listening test you could tell.  Which I know I've done.  I was even comparing some amps at home once and an old GF who had no interest in audio or electronics (but was a pianist and singer) could easily tell which amp was playing.  She had no idea which cost more or had the better reputation.  But consistently preferred one out of the three and recognized which of the other two were playing as well.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Pascal Pincosy on February 07, 2008, 07:18:27 pm
Richard Rajchel wrote on Thu, 07 February 2008 15:32

I couldn't agree more. Everyone likes to believe they have somewhat golden ears. When we all hear as much with our eyes and preconceived notions is closer to the truth. In blind tests with output matched and no "voltage" shutdowns etc... I doubt anyone could tell you which amp was a Lab and which one was an RMX. The results would be completely random. Aren't volts volts and amps just amps? There are most certainly nuances, and maybe one amp has a sag at a certain frequency, but with just about any two amps behind a curtain driving identical speakers with the identical program material at the identical voltage I can't imagine anyone could tell. Reliability, weight, and how an amp handles overloads or under powering would be far better criteria than how you think an amp might sound better than another.


The testing at my amp shootout was completely blind and I went so far as to change the numbering of the amps they were listening to several times, in order to trick people who developed a preference for a certain numbered amp. It seemed pretty clear to me that the participants were able to pick out the "better" sounding amps most of the time ie the results were not random. Further tested showed that different amps would sound "better" with some loudspeakers than they would with others. Testing with 4 different cabinets (the second set of tests was not blind) showed different "winners" for passive top cab, front-loaded sub, and horn-loaded sub. No one amp was the 'best". And FWIW, the RMX performed very well and actually improved on the Lab Gruppen's sound on top cabinets.

Was my testing statistically valid? No, but it's good enough for horseshoes. If somebody wants to hire me to sit around and test audio gear all day I'll be happy to come up with some definitive results though.  Very Happy
Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 07, 2008, 08:08:42 pm
Andy Peters wrote on Thu, 07 February 2008 07:24

Ted Olausson wrote on Wed, 06 February 2008 22:27

Quote:


I think the way that amps are used today they do have a "sound".  It is typical to see amps driven into the non linear mode.  In fact I think it has become commonplace.  That makes a smaller system sound "louder".  



http://www.moultonlabs.com/more/power_amps_revisited/


Well, he's driving easier loads at lower SPLs than typical for SR use and it's obvious that driving the amps to the edge all night is not a requirement.

But, really, it just sounds like the guy who built the amps conservatively rated them lower than what they can really do. Which is fine, and even laudable, especially considering that he leaves some "marketing watts" on the table.

Note how they measure SPL, but not amplifier output power, which would be the better test.



No, the SPL is the single most important part, or as the quote i answered to: Noone in PA actually wants a clean sounding rig, people wants loudness and cuttrough at 97dB , and if you remove distortion et al you wont get that, even at 120dB...

The article was a followup to an earlier ampshootout where he compared amps between 35 and 250w and concluded that they were all the same regardless of power, and in the followup he says that this one is different because his reaction to the SPL is different.
http://www.moultonlabs.com/more/what_is_the_sound_of_one_amp _clipping/

Anyway, all amplifiertests on speakers should be done with fullrangematerial without any kind of crossovers, the difference can be quite remarkable.(even a 1inch driver will hold for fullrange as long as the volume is sufficiently low)
Title: Re: Sound Is Subjective
Post by: Duncan McLennan on February 07, 2008, 08:20:08 pm
Home stereo or PA?  I can easily tell the difference between both hi-fi amps and pro audio amps in my home system, even under blind test conditions.  I've done it many times.

In a PA application, I don't consider it a serious issue.  If an amplifier will get through the night without thermaling, sound pretty good, not blow up my speakers, I'm a happy guy.

Lighting weight, and low current draw are nice bonuses.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Tim Duffin on February 07, 2008, 09:09:25 pm
Bob Leonard wrote on Wed, 06 February 2008 12:52

Andy Peters wrote on Wed, 06 February 2008 13:08

Bob Leonard wrote on Wed, 06 February 2008 08:02

Yes Tim, I am aware those are all tube circuits, and;

A class C amplifier is biased beyond cutoff. The class C amplifier like the class B amplifier will draw no current with no signal input but a class B will start to draw current as soon as a signal is applied and a class C will only start to draw current when the signal strength is sufficient to go beyond the bias level. The class C amplifier is not linear but is the highest in efficiency.

In all classes of amplifier the linearity of the amplifier is determined by it's class.

The APS-20 radar on an EC-121 Willy Victor used a class "C" amplifier. RTTY, CW are often used with class "C" amplifiers, but they can not be used with SSB.


As The Good Tim says, flat view, anyone? USE THE QUOTE BUTTON.

And how is this relevant to the topic at hand? Other than to get into another mudwrestle with Duffin?

Quote:

I posted these as classic examples, and being as basic as these classes of amplifier are I would think it may be good reading material for people who may want to understand amplifiers and how they operate. Guitar players may find interest in class A/B amplifier circuits especially if they use a Fender amplifier.


And the design goals of a guitar amplifier are at cross purposes with one designed for sound reproduction.

One is a tone generator, one is not.

So the discussion is rather pointless.

-a


Andy,
I don't care about Duffin. He asked for an answer and got it. And since when are class A/B amplifiers not a part of sound reproduction. I seem to remember working with many prior to the use of transistors in amplifier output stages. I don't remember saying anything about preamplifier circuits at all. Maybe that's where your confused. Besides that the above were used as examples of amplifier class in response to someone who doesn't understand the meaning of the word linear. Ever read an RCA tube manual? Regardless of the class most amplifiers can trace their roots back to those simplistic amplifiers of days gone by in some way or another.




Fine, Ill use the quote button.

Anyways, the correct answer for my question you did not get.  The circuit which is class C is called a "gyrator" and it is not used in audio as per JR's comment.  The reason why is because it conducts only for positive values of input-- so use your imagination as to what that looks like on a scope.  I can tell that whomever wrote your quote has very little grasp of what the circuit does-- or it is very outdated information.

"Biased beyond cutoff"---lol!  thats the funniest thing I have read all week.


T


Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Pascal Pincosy on February 07, 2008, 09:15:35 pm
Tim Duffin wrote on Thu, 07 February 2008 18:09

Anyways, the correct answer for my question you did not get.


'Scuse my language, but who gives a f*ck? This site, forum, and thread are discussing pro audio. No-one is reading this thread to find out which of the two of you has the bigger penis. Can we please move on and talk about something that matters, like cars or something?  Rolling Eyes
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Tim Duffin on February 07, 2008, 09:19:31 pm
You, of all people should talk Laughing Cuz PAS speakers are better than everything else, right Rolling Eyes

I wouldn't have said anything if the info was correct in the first place.  

T
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Pascal Pincosy on February 07, 2008, 09:38:10 pm
Tim Duffin wrote on Thu, 07 February 2008 18:19

I wouldn't have said anything if the info was correct in the first place.

If you intent was really to educate, you would have let it go after Andy and JR set Bob straight. Instead you just had to get another word in. That's exactly how you continue to earn your 'troll' reputation.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: John Roberts {JR} on February 07, 2008, 09:55:02 pm
Tim Duffin wrote on Thu, 07 February 2008 20:09




Fine, Ill use the quote button.

Anyways, the correct answer for my question you did not get.  The circuit which is class C is called a "gyrator" and it is not used in audio as per JR's comment.  The reason why is because it conducts only for positive values of input-- so use your imagination as to what that looks like on a scope.  I can tell that whomever wrote your quote has very little grasp of what the circuit does-- or it is very outdated information.

"Biased beyond cutoff"---lol!  thats the funniest thing I have read all week.


T





The gyrator circuits I am familiar with, I am only familiar with because they were used in audio. Capacitors and opamps were configured to mimic inductors in EQ circuits. Those gyrators absolutely conducted in both directions.

I see little value in talking about class C RF amps or even tube stuff here.. other than in passing.. see there it goes, it's passed. now wipe.

JR

PS.. fi fie fo fum, I smell a troll in the LAB lounge...
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Richard Rajchel on February 07, 2008, 10:00:50 pm
A bit more clarification.

Just the simple fact that anyone is using the word "better" makes it subjective in the first place. In the case where the RMX improved on some top cabinet sound over the Labs, what was it that made the RMXs "better". It had to be SPL in a "pleasing to the ear" range. For example at the level you were testing at the RMX/top cabinet combination had a slight rise in SPL for the frequency range from 2k-5k or something? Just an example, but if it's audible and repeatable you should be able to measure it.

Like different microphones have different response curves, as well as speakers etc... More expensive mics might be closer to flat response, and more accurate, but that doesn't make them sound better to our ear. That slight rise in response in the 1.5k-10k range of frequencies(even if it's only a dB or 2) tends to sound clearer, or cleaner, or more presence, or any other number of descriptions for that particular sound quality.

So maybe the RMX is just not quite as accurate as the Lab with those speakers, but the result is still pleasing to the ear. Change speakers and you get a different result perhaps as well.

The question is who's going to spend the rest of their lives and millions of dollars documenting which amps work the best with each speaker in every situation?

The QSC RMX 1450 is the best sounding amp on the compression driver of bi-amped monitor XYZ, but use a Crown MA3600 for the 15" speaker and cross them over at 108.64 hz., but if the temperature is below 71.5 Fahrenheit and voltage is above 114 then use a PLX 3002 on the compression driver.

It's all sooooo ridiculous...lol.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Tim Duffin on February 07, 2008, 11:33:04 pm
I don't agree.  How can you educate somebody without saying anything?  And btw-- this is the lounge, call me whatever you like--just don't be a sore loser. Laughing   The original post doesn't serve to educate or inform, so why should I?

T
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Jeff Hague on February 08, 2008, 12:08:19 am
Andy Peters wrote on Wed, 06 February 2008 15:40

Silas Pradetto wrote on Wed, 06 February 2008 13:35

Damping factor is the load impedance divided by the output impedance of the amplifier. This means, with an 8 ohm load and a .01 ohm output impedance of the amplifier, you would have a damping factor of 800. Damping factor has quite a bit to do with bass quality. It is related to cone control such that a higher damping factor is more control. If there is more control, the woofer flaps around less and relies less on it's own suspension to return it to the "zero" point in it's travel, making everything sound "punchier." I hope that kind of made sense.


You forget the salient point: overall damping factor is severely degraded by the cable between the amp and the driver, as that cable's resistance adds to the amp output impedance.

In fact, the cable resistance essentially sets the damping factor, making amplifier damping factor irrelevant except maybe as a marketing bullet point.

This horse is dead.

Please stop beating it.

-a


So, why wouldn't a higher damping factor be desirable anyway? If the copper between the amp and the speaker degrades it, wouldn't a higher damping factor to begin with cause less degradation? Is the effect that overwhelming (ie non-linear)? It seems to me that the effect of copper wire on damping factor is linear, as is the effect of speaker impedance. An amp with a damping factor of 200 into an 8 ohm load will have a damping factor of 100 into a 4 ohm load, right? In that light, the higher the damping factor of the amp to begin with (prior to the speaker cable), the better...

Ive never beat a dead horse that I didn't like...
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Andy Peters on February 08, 2008, 01:52:08 am
Jeff Hague wrote on Thu, 07 February 2008 22:08

Andy Peters wrote on Wed, 06 February 2008 15:40

Silas Pradetto wrote on Wed, 06 February 2008 13:35

Damping factor is the load impedance divided by the output impedance of the amplifier. This means, with an 8 ohm load and a .01 ohm output impedance of the amplifier, you would have a damping factor of 800. Damping factor has quite a bit to do with bass quality. It is related to cone control such that a higher damping factor is more control. If there is more control, the woofer flaps around less and relies less on it's own suspension to return it to the "zero" point in it's travel, making everything sound "punchier." I hope that kind of made sense.


You forget the salient point: overall damping factor is severely degraded by the cable between the amp and the driver, as that cable's resistance adds to the amp output impedance.

In fact, the cable resistance essentially sets the damping factor, making amplifier damping factor irrelevant except maybe as a marketing bullet point.

This horse is dead.

Please stop beating it.

-a


So, why wouldn't a higher damping factor be desirable anyway? If the copper between the amp and the speaker degrades it, wouldn't a higher damping factor to begin with cause less degradation? Is the effect that overwhelming (ie non-linear)? It seems to me that the effect of copper wire on damping factor is linear, as is the effect of speaker impedance. An amp with a damping factor of 200 into an 8 ohm load will have a damping factor of 100 into a 4 ohm load, right? In that light, the higher the damping factor of the amp to begin with (prior to the speaker cable), the better...

Ive never beat a dead horse that I didn't like...


See the charts at the end of this paper (pdf). Notice that the largest contribution to damping factor is indeed the cable resistance.

-a
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Bob Leonard on February 08, 2008, 09:47:38 am
Andy Peters wrote on Fri, 08 February 2008 01:52

Jeff Hague wrote on Thu, 07 February 2008 22:08

Andy Peters wrote on Wed, 06 February 2008 15:40

Silas Pradetto wrote on Wed, 06 February 2008 13:35

Damping factor is the load impedance divided by the output impedance of the amplifier. This means, with an 8 ohm load and a .01 ohm output impedance of the amplifier, you would have a damping factor of 800. Damping factor has quite a bit to do with bass quality. It is related to cone control such that a higher damping factor is more control. If there is more control, the woofer flaps around less and relies less on it's own suspension to return it to the "zero" point in it's travel, making everything sound "punchier." I hope that kind of made sense.


You forget the salient point: overall damping factor is severely degraded by the cable between the amp and the driver, as that cable's resistance adds to the amp output impedance.

In fact, the cable resistance essentially sets the damping factor, making amplifier damping factor irrelevant except maybe as a marketing bullet point.

This horse is dead.

Please stop beating it.

-a


So, why wouldn't a higher damping factor be desirable anyway? If the copper between the amp and the speaker degrades it, wouldn't a higher damping factor to begin with cause less degradation? Is the effect that overwhelming (ie non-linear)? It seems to me that the effect of copper wire on damping factor is linear, as is the effect of speaker impedance. An amp with a damping factor of 200 into an 8 ohm load will have a damping factor of 100 into a 4 ohm load, right? In that light, the higher the damping factor of the amp to begin with (prior to the speaker cable), the better...

Ive never beat a dead horse that I didn't like...


See the charts at the end of this paper (pdf). Notice that the largest contribution to damping factor is indeed the cable resistance.

-a




Nice chart Andy, thank you. It does certainly illustrate your point. Time to move on I would imagine. Very Happy
Title: Re: Sound Is Subjective
Post by: Dave Rickard on February 08, 2008, 10:48:09 am
Andy Peters wrote on Tue, 05 February 2008 16:39

Richard Rajchel wrote on Tue, 05 February 2008 14:11

One last thing about "punchy" bass. What the heck does that mean in reality? Most people, including a lot of engineers think to get a great kick drum sound you need subs that go to 20Hz flat(OK I'm exaggerating a little), but that "kick in the chest" feeling is usually in the 60-80Hz range, and in all actuallity the first harmonic of 120-160Hz is where most of that feel comes from.


Agreed. And furthermore, from which cabinet do you get that 160 Hz?

Answer: not the sub!

-a



Yes you do, from the subs, in the form of distortion.  At least in front loaded cabinets.  I was skeptical about this concept, and/or at least, how much harmonic content a driver adds.

When I got my horn subs back from the builder and was checking them out before finishing the raw wood.  I needed to seal and check for leaks around the doors, handles, yada.

While playing 40, 50, 60 Hz test sine waves with the access door open and closed, I could clearly hear harmonics which were not present in those sine waves.  Taking the door on and off clearly demonstrated this.  When the doors were on the folds in the horn filtered those overtones out.

I believe that's why some folks don't like the "horn sound", the lack of distortion, and prefer gobs of double 18's.

I don't recall what you use for subs at your club, but f you can get horn subs sometime you can verify this.


Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Dave Rickard on February 08, 2008, 11:03:57 am
Tim Duffin wrote on Thu, 07 February 2008 21:33

I don't agree.  How can you educate somebody without saying anything?


"An ignorant person is one who doesn't know what you have just found out."

"Never miss a good chance to shut up".

--Will Rogers (1879 - 1935)
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: John Roberts {JR} on February 08, 2008, 11:08:42 am
Jeff Hague wrote on Thu, 07 February 2008 23:08



So, why wouldn't a higher damping factor be desirable anyway? If the copper between the amp and the speaker degrades it, wouldn't a higher damping factor to begin with cause less degradation? Is the effect that overwhelming (ie non-linear)? It seems to me that the effect of copper wire on damping factor is linear, as is the effect of speaker impedance. An amp with a damping factor of 200 into an 8 ohm load will have a damping factor of 100 into a 4 ohm load, right? In that light, the higher the damping factor of the amp to begin with (prior to the speaker cable), the better...

Ive never beat a dead horse that I didn't like...


Well yes kind of...  The damping factor will never be better than the amp is capable of. So a flabby tube amp, won't sound any tighter with welding cable for speaker lines.

The effect of wire resistance on DF is reciprocal, so small increases in wire resistance cause large drops in DF. This is somewhat confused by amp marketers making a big deal about numerically high bench DFs that don't exist in real world use.

JR
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Pascal Pincosy on February 08, 2008, 12:32:20 pm
Richard Rajchel wrote on Thu, 07 February 2008 19:00

Just the simple fact that anyone is using the word "better" makes it subjective in the first place. In the case where the RMX improved on some top cabinet sound over the Labs, what was it that made the RMXs "better". It had to be SPL in a "pleasing to the ear" range. For example at the level you were testing at the RMX/top cabinet combination had a slight rise in SPL for the frequency range from 2k-5k or something? Just an example, but if it's audible and repeatable you should be able to measure it.

Like different microphones have different response curves, as well as speakers etc... More expensive mics might be closer to flat response, and more accurate, but that doesn't make them sound better to our ear. That slight rise in response in the 1.5k-10k range of frequencies(even if it's only a dB or 2) tends to sound clearer, or cleaner, or more presence, or any other number of descriptions for that particular sound quality.

So maybe the RMX is just not quite as accurate as the Lab with those speakers, but the result is still pleasing to the ear. Change speakers and you get a different result perhaps as well.

The question is who's going to spend the rest of their lives and millions of dollars documenting which amps work the best with each speaker in every situation?


I doubt that the +0/-1dB frequency response of the RMX series is audible, though I'm sure the +0/-3dB response of the Lab Gruppen FP10000Q is Shocked . But I think that there's more involved in how an amp sounds and responds than just frequency response. Speed of attack, power supply capacity, artifacts, and (for those with really short, fat speaker cables) damping Wink among other things will all make a difference in how an amp sounds.

It makes sense that if the goal of your PA design is the highest possible fidelity, that one would try different amps with ones loudspeaker of choice and pick the one that sounds the best for the given application. That's not going to cost you more than a few calls to your local dealers asking for demo units, and an afternoon of your time.

If the goal is getting the job done, then sure, buy based on features/weight/cost/reliability.
Title: front-loaded sub distortion
Post by: Andy Peters on February 08, 2008, 12:33:57 pm
Dave Rickard wrote on Fri, 08 February 2008 08:48

Andy Peters wrote on Tue, 05 February 2008 16:39

Richard Rajchel wrote on Tue, 05 February 2008 14:11

One last thing about "punchy" bass. What the heck does that mean in reality? Most people, including a lot of engineers think to get a great kick drum sound you need subs that go to 20Hz flat(OK I'm exaggerating a little), but that "kick in the chest" feeling is usually in the 60-80Hz range, and in all actuallity the first harmonic of 120-160Hz is where most of that feel comes from.


Agreed. And furthermore, from which cabinet do you get that 160 Hz?

Answer: not the sub!

-a



Yes you do, from the subs, in the form of distortion.  At least in front loaded cabinets.  I was skeptical about this concept, and/or at least, how much harmonic content a driver adds.

When I got my horn subs back from the builder and was checking them out before finishing the raw wood.  I needed to seal and check for leaks around the doors, handles, yada.

While playing 40, 50, 60 Hz test sine waves with the access door open and closed, I could clearly hear harmonics which were not present in those sine waves.  Taking the door on and off clearly demonstrated this.  When the doors were on the folds in the horn filtered those overtones out.

I believe that's why some folks don't like the "horn sound", the lack of distortion, and prefer gobs of double 18's.

I don't recall what you use for subs at your club, but f you can get horn subs sometime you can verify this.


We have two double-18" front-loaded subs at the stage front and center. Each box is powered by a channel of a Crest 8001 (and in over seven years I have NEVER seen the clip light blink). We feed both amp channels from the processor's mono sub out (simple split).

Ya know, if I had seen this post last night (or if you'd posted it last night!) while waiting for the band, I would have swept tones through the subs and measured it to see.

So what causes the distortion? Is it as simple as "overloading the box" in the sense that the output is clean up until some SPL level which essentially puts the system into saturation? Or is the distortion present at all levels? I am the first to admit that my knowledge of loudspeaker physics details is limited.

-a
Title: Re: front-loaded sub distortion
Post by: Tim McCulloch on February 08, 2008, 12:55:52 pm
Since distortion is the product of non-linear response.... anything that causes (or changes) non-linearity would be a contributing factor.

The propellor-beanie guys can explain all the components of that.

Have fun, good luck.

Tim Mc
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Bob Lee (QSC) on February 08, 2008, 03:10:34 pm
Hi Tim,

I used to work in broadcasting, and we never called it a "gyrator." To me, a gyrator is a circuit that mimics an inductor, which is useful in circuits like graphic EQs.

Class C generally involves a resonant tank circuit with fairly high Q and low damping, and the short conduction pulses of the transistor or valve are simply to excite the tank so it will oscillate for at least a number of cycles. Thus, it is useful for high-efficiency amplification of a single frequency continuous wave carrier, as well as for frequency multiplication by low-integer factors. The excitation of the tank can be with a positive- or negative-polarity pulse, depending on the configuration of the active device.
Title: Re: front-loaded sub distortion
Post by: Richard Rajchel on February 08, 2008, 03:59:53 pm
I think the distortion of front loaded subs in particular is the actual cone/box acting just like an instrument. I'm not a scientist, but I'm taking a good guess that yes, 160hz can be heard from a sub even if it's crossed at 100hz. The cone of the speeaker might be like the string on a piano, and the box that it's in would obviously be like the piano. Even though all the movement of the cone forwards and backwards is controlled by electrical signals from the amplifier, the actual cone itself has it's own "harmonics". If you pluck an e string on a guitar you can still hear an octave above that, perhaps another 5th above that, and them some really high harmonics that tend to give it a bit of a ring...the newer the strings the more pronounced the harmonics are because it's not all deadened by string degradation and oils from the skin of the fingers playing the guitar. This "cone/box" distortion or harmonics is more pronounced with an 18" driver simply because it's much bigger and not as rigid. You won't hear nearly as much harmonic content from the high E string on a guitar as you might from the low E string. Just like you won't hear as much harmonics/distortion from a 10" speaker as you would from a 18", or God forbid a 21" speaker.

That's my attempt at describing the distortion factor of front loaded 18" subs.

Horn loaded subs don't have nearly as much of that distortion because of design. All the shorter length sound waves don't make it around all those corners inside a folded horn, and in addition most horns use smaller drivers than 18" so there's less cone area and the cone is more rigid to not enhance these harmonics/distortion.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Jeff Hague on February 08, 2008, 05:06:36 pm
Andy Peters wrote on Fri, 08 February 2008 01:52

Jeff Hague wrote on Thu, 07 February 2008 22:08

Andy Peters wrote on Wed, 06 February 2008 15:40

Silas Pradetto wrote on Wed, 06 February 2008 13:35

Damping factor is the load impedance divided by the output impedance of the amplifier. This means, with an 8 ohm load and a .01 ohm output impedance of the amplifier, you would have a damping factor of 800. Damping factor has quite a bit to do with bass quality. It is related to cone control such that a higher damping factor is more control. If there is more control, the woofer flaps around less and relies less on it's own suspension to return it to the "zero" point in it's travel, making everything sound "punchier." I hope that kind of made sense.


You forget the salient point: overall damping factor is severely degraded by the cable between the amp and the driver, as that cable's resistance adds to the amp output impedance.

In fact, the cable resistance essentially sets the damping factor, making amplifier damping factor irrelevant except maybe as a marketing bullet point.

This horse is dead.

Please stop beating it.

-a


So, why wouldn't a higher damping factor be desirable anyway? If the copper between the amp and the speaker degrades it, wouldn't a higher damping factor to begin with cause less degradation? Is the effect that overwhelming (ie non-linear)? It seems to me that the effect of copper wire on damping factor is linear, as is the effect of speaker impedance. An amp with a damping factor of 200 into an 8 ohm load will have a damping factor of 100 into a 4 ohm load, right? In that light, the higher the damping factor of the amp to begin with (prior to the speaker cable), the better...

Ive never beat a dead horse that I didn't like...


See the charts at the end of this paper (pdf). Notice that the largest contribution to damping factor is indeed the cable resistance.

-a



So, I read it again, and then again... It takes a few times through to see your point and I agree. It sounds to me that the cable is significant if its more than 50 feet. So, does that mean then that the amps DF is siginificant in a powered sub?
What I find most interesting is that they say a DF of 20 is adequate which would mean that even in a powered sub, it really doesnt matter.
I remember years ago being told that 200 was average and "OK" for an 8 ohm load but if your subs were 4, youd better find something higher. I also remember eying Crest amps boasting DFs of 1000. Good thing I couldnt afford Crest then I guess...
Thanks!
Title: Re: front-loaded sub distortion
Post by: Bob Leonard on February 08, 2008, 05:40:37 pm
Richard Rajchel wrote on Fri, 08 February 2008 15:59

I think the distortion of front loaded subs in particular is the actual cone/box acting just like an instrument. I'm not a scientist, but I'm taking a good guess that yes, 160hz can be heard from a sub even if it's crossed at 100hz. The cone of the speeaker might be like the string on a piano, and the box that it's in would obviously be like the piano. Even though all the movement of the cone forwards and backwards is controlled by electrical signals from the amplifier, the actual cone itself has it's own "harmonics". If you pluck an e string on a guitar you can still hear an octave above that, perhaps another 5th above that, and them some really high harmonics that tend to give it a bit of a ring...the newer the strings the more pronounced the harmonics are because it's not all deadened by string degradation and oils from the skin of the fingers playing the guitar. This "cone/box" distortion or harmonics is more pronounced with an 18" driver simply because it's much bigger and not as rigid. You won't hear nearly as much harmonic content from the high E string on a guitar as you might from the low E string. Just like you won't hear as much harmonics/distortion from a 10" speaker as you would from a 18", or God forbid a 21" speaker.

That's my attempt at describing the distortion factor of front loaded 18" subs.

Horn loaded subs don't have nearly as much of that distortion because of design. All the shorter length sound waves don't make it around all those corners inside a folded horn, and in addition most horns use smaller drivers than 18" so there's less cone area and the cone is more rigid to not enhance these harmonics/distortion.


Richard,
This is not a very good analogy. First, if I were able to hear the second octave note, or any note, that I am not playing on any of my guitars not plugged into an amplifier I would be very concerned that the instrument were defective. And I know my doctor and close friend would dump both his baby grands if that were the case as well.

Now I'm not going to turn this discussion into a lesson on guitar amps. The point is the example you used, so I feel some comparison is in order to dispel the myth. However, audio distortion is the same regardless of source.

http://www.blackstoneappliances.com/dist101.html

If I plug that same guitar into a guitar amplifier, preamp and power amp, and do not hear the 2nd and 3rd order harmonics, a by product of distortion (actually distortion), then I will reject the amp for just the opposite reason I would reject the guitar. In the design of most quality instrument/guitar amps those harmonics are a goal. It's the difference between good sounding and bad sounding distortion, or call it brown sound if you like for us blues players.

A power amplifier that is designed to be linear has very little distortion at all, and certainly there should be no distortion you can hear when the amplifier is used within spec. The sole purpose is, once again, to reproduce the incoming signal at a higher level without distortion. A point may be that the QSC RMX4050HD exhibits distortion that is Less than 0.02% @ 4 ohms, less than 0.01% @ 8 ohms at full rated power, 4000 watts. The preamplifier for an amp is of course your desk, so if your board has poor specs, then your amplifier used within spec should and does only replicate what it's told to replicate, distortion and all.

Speakers do distort, so speaker choice remains as a factor. However good speakers don't distort to the point where a second note should be discernible, because if that were the case the speaker would be unusable. And generally speakers for guitar are actually chosen for their ability to "break up" in a pleasant way. In a way our ears find enjoyable depending on the musical content, but you won't hear a second note. You'll hear a 2nd or third order harmonic to that note, a note that is in harmony with the note being played. 25 watt speakers are often used in 50 watt guitar amplifiers just for that reason.

Speakers that are used for sound reinforcement are designed to be void of these problems. Good speakers do not distort at their rated power, because if they did, the power rating would have to be lowered. Good speakers, regardless of size, have distortion ratings well below what is audible to the human ear while listening to the program content. Is it there? Maybe but I would doubt you'll hear it. Here's a link to my favorite 18" speaker. Note the distortion characteristics for the speaker within it's usable frequency range vs. the output. That should answer the question.

http://www.jblpro.com/pages/pub/components/2242.pdf

Can the cabinet be oscillating and actually reproducing a second note? Yes, but bracing the cabinet or thicker wood should solve that problem.

My take on all this, as it has been forever, is that although an audio amplifier reproduces sound in a linear fashion, it is impossible for any amplifier to reproduce the entire audible frequency range at 40hz with the same efficiency as that same amplifier will reproduce signals at 10khz, or vice versa. In some amps it's noticible, in others it is not.

I have always thought that an amplifier optimized to handle frequencies 200hz to 20hz would be a wonderful thing. It should put out 1000 per channel, 5000 watts bridged, and QSC should call it the the BFSA5000.  

It's never just one piece of the puzzle, and these are just more thoughts to ponder.

IBBY,
Bob L.
Title: Re: front-loaded sub distortion
Post by: Richard Rajchel on February 08, 2008, 06:06:14 pm
Possibly you are confusing intentional guitar distortion and the harmonics which are present in every musical note. If you pluck a single string on a guitar there will be harmonics present. It's the same harmonic overtone series a trumpet player uses to play higher notes. Octave, fifth, next octave, then the third and so on. Or the harmonic series on a guitar string...exactly the same as what you hear, only when you touch the guitar string at the halfway point you dampen the fundamental and only hear the 1st octave harmonic. I'm not arguing the engineering aspect of amps and speakers.

How do you think you can hear a low E on a bass guitar(41hz) on speakers that might be able to only go down to 100hz? It's harmonics that you hear. In my experience the lower the note the more prevalent the harmonics are. It's much easier to hear them with a low E on a bass than a high E on a guitar. That's just personal experience. I'm sure someone has a scientific explanation for that.

Haven't you ever seen the charts that show harmonic distortion of speakers? That's actual measurements of what's going on. Not some mythical defective piano. Actually a grand piano is probably one of the easiest instruments there is to hear the overtones on...especially the lower notes.
Title: Re: front-loaded sub distortion
Post by: Joe Breher on February 08, 2008, 06:17:49 pm
Bob Leonard wrote on Fri, 08 February 2008 15:40


This is not a very good analogy. First, if I were able to hear the second octave note, or any note, that I am not playing on any of my guitars not plugged into an amplifier I would be very concerned that the instrument were defective.


I am curious - if a guitar only puts out the fundamental, why does an ES-175 sound mellower than a Tele? The fact of the matter is that guitars put out a very rich overtone series. Indeed, on the low strings, there is frequently more energy in the first few harmonics than in the fundamental. Smaart it if you don't believe me. Or, lacking Smaart, even just look at the string vibration pattern under a strobe light. You will notice the nodes formed from the various harmonics.

Quote:

Speakers that are used for sound reinforcement are designed to be void of these problems. Good speakers do not distort at their rated power, because if they did, the power rating would have to be lowered. Good speakers, regardless of size, have distortion ratings well below what is audible to the human ear while listening to the program content. Is it there? Maybe but I would doubt you'll hear it. Here's a link to my favorite 18" speaker. Note the distortion characteristics for the speaker within it's usable frequency range vs. the output. That should answer the question.

http://www.jblpro.com/pages/pub/components/2242.pdf



I see that JBL claims a < 1.0% distortion figure. That sounds pretty good. However, they claim it a 10 dB below rated power (80 W, instead of 800 W). They also claim it for the frequency range of 100 Hz-500 Hz, which is conveniently where the accompanying graph shows the distortion 'bottoms out'. Why didn't they rate the distortion at a sub frequency range - such as 50-100Hz? Or at  full rated output? Probably because it would be significantly higher than the 1% claimed figure.

Not that I followed the OP's piano analogy. However, it seems to me that you are dismissing the possibility that the driver can contribute significant distortion on its own.
Title: Re: front-loaded sub distortion
Post by: Tony "T" Tissot on February 08, 2008, 06:33:49 pm
Bob Leonard wrote on Fri, 08 February 2008 14:40

This is not a very good analogy. First, if I were able to hear the second octave note, or any note, that I am not playing on any of my guitars not plugged into an amplifier I would be very concerned that the instrument were defective. And I know my doctor and close friend would dump both his baby grands if that were the case as well.
IBBY,
Bob L.


As "fundamental" a law as inverse square.

No truly pure tones exist from any instrument.

Pianos and other stringed instruments really exhibit this (whatever the correct terminology is).


From http://www.vibrationdata.com/piano.htm


The beginning key on the left end is an A0 note with a fundamental frequency of 27.5 Hz. A piano key has harmonic overtones at integer multiples of its fundamental frequency. Thus, the A0 key also produces a tone at 55.0 Hz, which is one octave higher than the fundamental frequency. The second overtone is at 82.5 Hz.

add reference.
Title: Re: front-loaded sub distortion
Post by: Richard Rajchel on February 08, 2008, 06:43:31 pm
About Bob's favorite JBL chart. That only shows down to 90 dB. That distortion is still present whether it's on the chart or not.
Title: Re: Sound Is Subjective
Post by: Ian Hunt on February 08, 2008, 07:00:33 pm
Infrasonics?

Once again I am reminded of a comment at a trade show (many years ago) from a speaker designer: he said "frequencies below 20hz are called weather where I come from"

But I am not sure that because they are felt rather than heard means that they have no effect?

Title: Re: Sound Is Subjective
Post by: Ian Hunt on February 08, 2008, 07:04:23 pm
"An amp should have no "sound" ... good or bad if we use the old standard ...striaght wire with gain"

All well and good but you seem to be suggesting that we have somehow achieved a state of perfection with amplifier design, I am not so sure. I do believe that amplifiers are not all alike sonically, but the differences tend to be orders of magnitude lower than in other areas (transducers especially)

Title: Re: Sound Is Subjective
Post by: Ian Hunt on February 08, 2008, 07:23:54 pm
Not sure about your 50% number for class A but whatever, they are not very efficient in real life ... but

Having owned and used a pair of ancient 25w class A amplifiers (solid state) for a long time I must say I like the way they sound.

Would I want one as a PA amp? lets see, 107lbs for 25w x 2

NO
Title: Re: front-loaded sub distortion
Post by: Andy Peters on February 08, 2008, 07:45:23 pm
Richard Rajchel wrote on Fri, 08 February 2008 13:59

I'm not a scientist, but I'm taking a good guess that yes, 160hz can be heard from a sub even if it's crossed at 100hz.


This may be the major factor, as 160 Hz will only be down 10.4 dB (assume 4-pole Butterworth low-pass at 100 Hz). That's pretty loud, esp. if your subs are doing 120 dB in their passband at 1 meter during actual use. TANSTAABWF.

I'm sure the cone/driver motor assembly does have some distortion products (read: harmonics_, especially if not damped (let's not talk about that!) or if the cone material isn't stiff enough.

I suppose I could grab one of the cabinet modeling programs and see what's what, but I suspect that a horn's cut-off attenuates the distortion.

-a
Title: Re: front-loaded sub distortion
Post by: Greg Cameron on February 08, 2008, 07:55:52 pm
Richard Rajchel wrote on Fri, 08 February 2008 12:59

I'm not a scientist, but I'm taking a good guess that yes, 160hz can be heard from a sub even if it's crossed at 100hz.


While all drivers create extra harmonics above a fundamental note, also be aware the a crossover is not an absolute cut-off point at the knee. A 24 dB/octave slope for a 100Hz xover means the energy will be 24 dB down at 200Hz for the sub. There will still be noticeable and significant energy at 160Hz. If the crossover slope happens to be a slower roll off, then that much more energy past the knee will be present. If you have a chance to frequency sweep your subs set at 100Hz, you'd be surprised how much gets through above that point. Same for all the other drivers in a system. I remember the first time I did a sweep on a 24dB crossover. I though it was broken because of how much energy there is even past the 24dB down point. A real wake-up call.

Greg
Title: Re: front-loaded sub distortion
Post by: John Roberts {JR} on February 08, 2008, 08:01:16 pm
Tony "T" Tissot wrote on Fri, 08 February 2008 17:33



No truly pure tones exist from any instrument.



The flute played pianissimo is pretty damn close from a real instrument, if we ignore synths that could but typically don't put out pure tones.

Most musical  instruments generate their notes using what I would call a one path  resonator, and will generate harmonics that are simple multiples of that path, i.e. string length, for plucked, struck, or bowed instruments, or acoustic path length for wind instruments.

In contrast there are instruments who generate overtones that are not simple multiples (harmonics) because of using different length paths for fundamental and overtone resonances (like them round drumheads).

To contrast the contrast we have instruments like tympani that are engineered to sound tonal, but the note you perceive is not even the note that is being voiced in a little psychoacoustic manipulation of our perception (we hear a lower frequency "phantom" fundamental that is the difference between the resonances).

Never say never, nature loves exceptions to any rule.


JR

Title: Re: Sound Is Subjective
Post by: Greg Cameron on February 08, 2008, 08:04:19 pm
In reality, infrasonics technically are below 20Hz, so my terminology was incorrect. I'll restate that my meaning was sub 30Hz information which is technically not infrasonic. That said, there is a difference between a rig that can reproduce information into the 20's with substantial energy vs. one that doesn't go much below 40, and the difference isn't subtle. Mr. Rajchel in a previous thread implied that regular rock music had no reason to need reinforcement that low. I submit that he's mistaken. As the phrase goes, "don't knock it until you've tried it."  As with so many things in life, you can't really judge until you've had the actual experience. While it's obviously not necessary to have a system with that capability, it certainly add an extra dimension to the performance which at least I and several other I know find preferable.

Greg
Title: Re: front-loaded sub distortion
Post by: Richard Rajchel on February 08, 2008, 08:13:48 pm
I'm not sure what the horn cutoffs are based on, but I would suspect that would be the correct terminology. Wavelengths shorter than a certain frequency just can't "escape" the horn. It seems that this has something to do with the sharp angles in most folded horn subs. Not sure if the shorter wavelengths just refelct too much and cancel each other out or what the physics behind it are, but curved horns don't attenuate the higher frequencies anywhere near as much. For example Bill Fitzmaurice's DR series speakers have curved horns and charts seem to suggest that the frequency rang of the mid driver has quite a wide range compared to a folded sub like the LAB. Those DRs are curved horns, not really folded. I think something similar is used in some Nexo line array systems. They use reflections of some kind, but they are based on some geometrical cross section of a sphere. I've seen the links here on PSW about that NEXO design as well.

One question I would have for someone more knowledgeable than me is would a straitened out LAB horn have the same distortion reduction as the folded version? My guess would be no, but of that I'm not sure.
Title: Re: front-loaded sub distortion
Post by: Tony "T" Tissot on February 08, 2008, 08:14:32 pm
John Roberts  {JR} wrote on Fri, 08 February 2008 17:01

Tony "T" Tissot wrote on Fri, 08 February 2008 17:33



No truly pure tones exist from any instrument.



The flute played pianissimo is pretty damn close from a real instrument, if we ignore synths that could but typically don't put out pure tones.

Most musical  instruments generate their notes using what I would call a one path  resonator, and will generate harmonics that are simple multiples of that path, i.e. string length, for plucked, struck, or bowed instruments, or acoustic path length for wind instruments.

In contrast there are instruments who generate overtones that are not simple multiples (harmonics) because of using different length paths for fundamental and overtone resonances (like them round drumheads).

To contrast the contrast we have instruments like tympani that are engineered to sound tonal, but the note you perceive is not even the note that is being voiced in a little psychoacoustic manipulation of our perception (we hear a lower frequency "phantom" fundamental that is the difference between the resonances).

Never say never, nature loves exceptions to any rule.


JR




"Close" does not an exception make  Razz

The search for exception has been fruitless. Even electronic instruments (although not in my consideration for the above mentioned "instrument") suffer when voiced through transducers.

No truly pure tones exist from any instrument.

Title: Re: Sound Is Subjective
Post by: Richard Rajchel on February 08, 2008, 08:19:15 pm
Like I said in that thread you are referring to, it may very well add to the experience, but it's not sound if it's infrasonics. Below 30hz is different than what you originally described, and yes there may be audible stuff below 30hz, but that's a bit different that what you originally described. My question then, is if the lowest sound producing instrument on a stage is a 4 string bass with a low E at 41hz, where is the material below that coming from? Is it like the reverse of harmonics?
Title: Re: front-loaded sub distortion
Post by: Ted Olausson on February 08, 2008, 08:32:17 pm
Richard Rajchel wrote on Sat, 09 February 2008 02:13

One question I would have for someone more knowledgeable than me is would a straitened out LAB horn have the same distortion reduction as the folded version? My guess would be no, but of that I'm not sure.


It is the frontchamber that acts as an acoustic lowpassfilter.
However, horns dont only have less distortion than a sealed box because of the LPfilter. BR and bandpass is a different story, since they rely on resonances.
Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 08, 2008, 08:42:36 pm
Duncan McLennan wrote on Fri, 08 February 2008 02:20

Home stereo or PA?  I can easily tell the difference between both hi-fi amps and pro audio amps in my home system, even under blind test conditions.  I've done it many times.


It doesnt matter where the speaker is. It is the amount of distortion added by the speaker that is important, and that will be atleast 90% of the final result anyway.


Quote:


In a PA application, I don't consider it a serious issue.  If an amplifier will get through the night without thermaling, sound pretty good, not blow up my speakers, I'm a happy guy.
Lighting weight, and low current draw are nice bonuses.


Nobody said that you should change a winning concept.
I only said that you should be aware of the fact that there still is a long way of technical development left to achieve the perfect sound.
Title: Re: Sound Is Subjective
Post by: Richard Rajchel on February 08, 2008, 08:52:04 pm
Quote:


Nobody said that you should change a winning concept.
I only said that you should be aware of the fact that there still is a long way of technical development left to achieve the perfect sound.


And that's not achievable because the perfect sound is different for everyone.
Title: Re: front-loaded sub distortion
Post by: John Roberts {JR} on February 08, 2008, 08:55:04 pm
Tony "T" Tissot wrote on Fri, 08 February 2008 19:14



"Close" does not an exception make  Razz

The search for exception has been fruitless. Even electronic instruments (although not in my consideration for the above mentioned "instrument") suffer when voiced through transducers.

No truly pure tones exist from any instrument.




A synth can output an arbitrarily pure tone. The pianissimo  flute is 95% fundamental. 5% for all harmonic content means the sum of all harmonics is down 26dB. Yes that -26 dB can be heard if it's in the right frequency range under very close listening, but in a musical performance I believe it would sound like a pure tone.

I guess if you draw your line finely enough, nothing is a pure tone. You win, no mas...

JR


Title: Re: Sound Is Subjective
Post by: Jeff Hague on February 08, 2008, 10:25:59 pm
Richard Rajchel wrote on Fri, 08 February 2008 20:19

Like I said in that thread you are referring to, it may very well add to the experience, but it's not sound if it's infrasonics. Below 30hz is different than what you originally described, and yes there may be audible stuff below 30hz, but that's a bit different that what you originally described. My question then, is if the lowest sound producing instrument on a stage is a 4 string bass with a low E at 41hz, where is the material below that coming from? Is it like the reverse of harmonics?


Reverse harmonics? They go both ways dont they?
In any case, there are processors on the market that add what they call subharmonics so, although it doesnt actually exist coming from the instrument, it can be synthesized. I was just looking at powered subs last night and came across one made by Crest (the amp people) that includes a subharmonic synth in the DSP before the amp. Its a single 15" bass reflex, pretty small - looked like about 24" by 30" by 20" or so, 1000 watts RMS and they claim 133dB at 33Hz!

Edit - I found another site that says the Crest does 128dB at 33Hz - big difference. There are unfortunately no specs on the Crest Performance site for this thing, just press releases...
Title: Re: front-loaded sub distortion
Post by: Bob Leonard on February 08, 2008, 11:06:11 pm
Tony "T" Tissot wrote on Fri, 08 February 2008 18:33

Bob Leonard wrote on Fri, 08 February 2008 14:40

This is not a very good analogy. First, if I were able to hear the second octave note, or any note, that I am not playing on any of my guitars not plugged into an amplifier I would be very concerned that the instrument were defective. And I know my doctor and close friend would dump both his baby grands if that were the case as well.
IBBY,
Bob L.


As "fundamental" a law as inverse square.

No truly pure tones exist from any instrument.

Pianos and other stringed instruments really exhibit this (whatever the correct terminology is).


From http://www.vibrationdata.com/piano.htm


The beginning key on the left end is an A0 note with a fundamental frequency of 27.5 Hz. A piano key has harmonic overtones at integer multiples of its fundamental frequency. Thus, the A0 key also produces a tone at 55.0 Hz, which is one octave higher than the fundamental frequency. The second overtone is at 82.5 Hz.

add reference.


Tony this is correct. What the ear hears are overtones, not a second note. More precisely the human ear wants to hear a combination of even and odd harmonics which we perceive as pleasent. On a guitar an open E string and the same string played on the 12th fret is still an E. However, as I said above I don't expect to or want to hear the E note as could be played on the 12th fret although I might hear some second and third order, or sypathetic harmonics that would add to the fullness of the sound.

An A musical note one octave lower would have a fundamental pitch of 440.0/2 hertz and an A note one octave higher would have a pitch of 2
Title: Re: front-loaded sub distortion
Post by: Dave Rickard on February 08, 2008, 11:44:33 pm
Andy Peters wrote on Fri, 08 February 2008 10:33

We have two double-18" front-loaded subs at the stage front and center. Each box is powered by a channel of a Crest 8001 (and in over seven years I have NEVER seen the clip light blink). We feed both amp channels from the processor's mono sub out (simple split).

Ya know, if I had seen this post last night (or if you'd posted it last night!) while waiting for the band, I would have swept tones through the subs and measured it to see.

So what causes the distortion? Is it as simple as "overloading the box" in the sense that the output is clean up until some SPL level which essentially puts the system into saturation? Or is the distortion present at all levels? I am the first to admit that my knowledge of loudspeaker physics details is limited.

-a


I don't have science on this, only my observations.  It wasn't due to amp clipping, or even high power.  I wasn't pushing the horns, just listening at low levels for leaks at the hardware.

I don't know what causes the distortion either, maybe someone else can explain this.  It's my understanding that folded horns, like the LabSub, filter out the naturally occurring distortion.  I just assumed it was there.

Since you mentioned measuring, it occurs to me that this should show up on any front loaded subwoofer sweep.  Hmmm....
Title: Re: Sound Is Subjective
Post by: Andy Peters on February 08, 2008, 11:46:50 pm
Richard Rajchel wrote on Fri, 08 February 2008 18:19

Like I said in that thread you are referring to, it may very well add to the experience, but it's not sound if it's infrasonics. Below 30hz is different than what you originally described, and yes there may be audible stuff below 30hz, but that's a bit different that what you originally described. My question then, is if the lowest sound producing instrument on a stage is a 4 string bass with a low E at 41hz, where is the material below that coming from? Is it like the reverse of harmonics?


A beat frequency?

-a
Title: Re: Sound Is Subjective
Post by: Tim McCulloch on February 08, 2008, 11:56:14 pm
Andy Peters wrote on Fri, 08 February 2008 22:46

Richard Rajchel wrote on Fri, 08 February 2008 18:19

Like I said in that thread you are referring to, it may very well add to the experience, but it's not sound if it's infrasonics. Below 30hz is different than what you originally described, and yes there may be audible stuff below 30hz, but that's a bit different that what you originally described. My question then, is if the lowest sound producing instrument on a stage is a 4 string bass with a low E at 41hz, where is the material below that coming from? Is it like the reverse of harmonics?


A beat frequency?

-a


The "beat" is used to create a low pedal stop in pipe organs, typically called a "Resultant (or Rezultant)."  Usually at 32' pitch, it's done by wiring the stop so that two notes play (bourdon or diapason voices, usually), and the resultant beat frequency is a unison note at 32' pitch.

One gets a bottom octave without having to have the room for 32' pipes.  No, it doesn't sound like a real rank of 32's, but it "sounds" and for 12 notes pitched that low, it's sufficient.

Have fun, good luck.

Tim Mc
Title: Re: Sound Is Subjective
Post by: Dave Rickard on February 08, 2008, 11:57:37 pm
Jeff Hague wrote on Fri, 08 February 2008 20:25

Reverse harmonics? They go both ways dont they?


Absolutely, but we call it different things.  When two flutes, or two bars on a glockenspiel play simultaneously, you can clearly hear other lower notes.  It can be very annoying.

I believe science labels it "intermodulation distortion".  Piano tuners call them beats, guitarists use it to tune harmonics.
Title: Re: Sound Is Subjective
Post by: Richard Rajchel on February 09, 2008, 04:41:47 am
Interesting stuff about pipe organs and combinations of tones. That's why I'm enjoying my time here on PSW so far.

I'm getting a college degree in real sound for the cost of my DSL connection. Not BS theories and stuff from guys who say "That's the way it is because that's the way we've always done it."

I also get what Bob is saying about not wanting to hear another note. I guess that's not exactly what I meant, and the higher the note the less of the overtones are heard, but on lower tones, and especially on acoustic instruments the overtones are heard easily. That's not to say that that is the main tone heard, just that they are audible and effect what we hear.
Title: Re: front-loaded sub distortion
Post by: Elliot Thompson on February 09, 2008, 05:31:17 am
Quote:


So what causes the distortion? Is it as simple as "overloading the box" in the sense that the output is clean up until some SPL level which essentially puts the system into saturation? Or is the distortion present at all levels? I am the first to admit that my knowledge of loudspeaker physics details is limited.

-a



Your assumptions about overloading the driver and/or amplifier is correct.

Notice those that carry ample amount of subs/amplifiers never complain about distortion?

It's the wonders of headroom which many have abandoned like pop music Cds constantly staying in 0 dB at all times.

Many are so concerned with xmax and maximum SPL that they focus primarily on that. There is nothing wrong choosing that route. However, when one is compromising (Trying to Get the most SPL/Xmax out of the least amount of boxes) they are more prone to encounter distortion than those who merely add more cabinets/amplifiers when the need arise.

You can't expect 4 subs to cover 1000 screaming fans effectively oppose to 16 with room to spare. Unfortunately many don't understand this and, find themselves blaming the tools when the user is as fault.


All speakers are subjected to distortion if/when they are pushed beyond their limits. Whether you choose Horn-Loads or Reflex cabinets.


Best Regards,
Title: Re: front-loaded sub distortion
Post by: Richard Rajchel on February 09, 2008, 05:41:16 am
I disagree.

Distortion by over powering a subwoofer is not what we are discussing here I don't think. That would be what we do to guitar cabinets on purpose to get "that sound".

I would guess that all speakers have distortion at all power levels. The amount of distortion likely increases as the power increases. It should also be mentioned that the sound of a front loaded double 18" subwoofer may have a more pleasing sound to some BECAUSE of the distortion. It's what many people are used to hearing. I'm guessing that it can be reduced by running well below the power maximum, but not eliminated. Certainly not in front loaded designs or any design for that matter. Folded horn subs have much less distortion, but it's still there.
Title: Re: Sound Is Subjective
Post by: Elliot Thompson on February 09, 2008, 06:09:52 am
Dave Rickard wrote on Fri, 08 February 2008 15:48



I believe that's why some folks don't like the "horn sound", the lack of distortion, and prefer gobs of double 18's.








Horns offer distortion as well. If you beg to differ, try to run  a frequency below the horns cutoff rate and the answer will be clear. The limiting factor is not the box but the speaker. Once you exceed the speaker's limitations distortion will come into to play. There is no exceptions to this rule. Once you exceed the box effective bandpass, you can expect distortion to come into play for the woofer has to do all the work.

The reason why many like the "Horn Sound" for bass is due to  majority of the horn-loaded boxes available today take a nose dive under 55 Hertz. The energy these boxes deliver above that is so enormous that many are intrigued with their efficency. And because Punchy Bass resides above 55 Hertz many are content with that type of sound.

However, for those that require 50, 40, & 30 Hertz will not find these boxes good enough for they lack low frequency extension. With the exception of two to three horn-loaded cabinets there isn't anything in the market that offers the extension as a reflex.

Personally, I need my subs to pick up where my mids leave off and continue down into the mid 30's. The only Horn-Loaded cabinets that will reach that far available today are the Bassmaxx B Zero, TRIP, Lab Sub, and Wayne Parham's (SP?) creation.

When my mid cabinets can go all the way down to 60 @ -3dB (I roll them off at 90 Hertz 12 dB slope), there is no way I'm going to invest in horn-loaded cabs that are 10 dBs down at 40 Hertz where my relex cabs are still hovering around 1- 1.5 dB down at 40 Hertz.

We all have our demands and requirements which is why there is no industry standard when it comes to subs.

Best Regards,



Title: Re: Sound Is Subjective
Post by: Richard Rajchel on February 09, 2008, 06:23:44 am
Once again I disagree. There is ALWAYS distortion present....not just when you over power a speaker.

In addition many horn loaded subs including the ones you mentioned will go pretty flat into the 30s. You do need multiples to do it, but with the added efficiency of the horn you need less of them to reach a certain SPL that similar front loaded cabinets. It's not really trivial either. I highly efficient front loaded design may push 100 dB 1w/1 meter, but a highly efficient horn loaded design will be more like 106+ dB 1w/1 meter. Doubling power gains you 3dB so double once again to reach a 6dB increase. You need 4 X the amount of front loaded enclosures to reach the output of 1 horn loaded design...of course these are just estimates. 4 LABs would probably crush 8 or 10 front loaded 18s at 1/2 the power or less...and in a group of 4 would go well into the 30s relatively flat.

You are correct that horns have distortion also, but it is much less than in front loaded designs.

I'm not sure where you see horn loaded subs that roll off 10dB by 40Hz...i'd like to see those, or at least know what they are so I can avoid them when looking to upgrade my rig.
Title: Re: front-loaded sub distortion
Post by: Elliot Thompson on February 09, 2008, 06:49:59 am
Richard Rajchel wrote on Sat, 09 February 2008 10:41

I disagree.

Distortion by over powering a subwoofer is not what we are discussing here I don't think. That would be what we do to guitar cabinets on purpose to get "that sound".

I would guess that all speakers have distortion at all power levels. The amount of distortion likely increases as the power increases. It should also be mentioned that the sound of a front loaded double 18" subwoofer may have a more pleasing sound to some BECAUSE of the distortion. It's what many people are used to hearing. I'm guessing that it can be reduced by running well below the power maximum, but not eliminated. Certainly not in front loaded designs or any design for that matter. Folded horn subs have much less distortion, but it's still there.



Read what I mentioned in my previous post about the type of bass majority of the bass horns offer today.

The woofer works less in horn (Within the horn's bandpass) however, is still subject to the amount of distortion as a reflex once driven beyond its limits.  

The way to overide the problem is to use more boxes and more
amplifiers to increase the headroom. Less distortion comes from having ample amount of headroom from your amplifiers and, the least amount of xmax used.

I'll use QSC as an example.

If QSC's LED indictors is -20 dB away from clipping and, the double eighteen woofer offers a 9mm Xmax each driver. In which, you are using 1 mm out of 9, with an end result of having all the SPL needed to cover the venue, you shouldn't have any distortion from a reflex cabinet unless the distortion is coming the source. The source being the processors, mic, or pre-recorded track.


You will find more bad sounding reflex cabinets in the market because they are more forgiving to mistakes by the designer.
There's also compromise in the enclosure based on the overall size. Those who rely heavily on eqing in order to achieve the extension needed to get the job done are subjected to more distortion. Reason being, the xmax needs to make up what the box cannot produce thus, increase distortion. If the box is big enough to offer a flat signal (0 dB Normalize gain) at 40 Hertz, xmax is reduced significantly oppose trying to attain 40 Hertz from a cabinet that is -10 dB @ 40 hertz and raising the EQ by 10 dBs to make up the gain. That box that is -10 dB down @ 40 Hertz will require more xmax from the driver to deliver the same SPL as the the box sitting @ 0 dB Normalized Gain. The end result is more distortion from the EQ'd driver.

Horns require you to have a full understanding on what you are trying to acomplish or you will end up with waisted wood. So, there are more good horn designs on the market than reflex designs.

     

Best Regards,





Title: Re: front-loaded sub distortion
Post by: Richard Rajchel on February 09, 2008, 07:07:59 am
OK, enough is enough. You keep claiming that at -20dB or what ever power level you choose that there is no distortion. Well I went to Turbosounds website and procured Turbosound's own SPL Chart for the TSW-718. It's a front loaded double 18" subwoofer of pretty decent quality.

http://www.ubersales.com/images/frequency.gif

As you can see the 2nd harmonic and 3rd harmonic distortion are quite present at only 10% power.

Where are your magical no distortion subwoofers?
Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 09, 2008, 07:44:32 am
Richard Rajchel wrote on Sat, 09 February 2008 02:52

Quote:


Nobody said that you should change a winning concept.
I only said that you should be aware of the fact that there still is a long way of technical development left to achieve the perfect sound.


And that's not achievable because the perfect sound is different for everyone.



Technically no.
Artistically, yes definately!
Title: Re: Sound Is Subjective
Post by: Elliot Thompson on February 09, 2008, 07:57:58 am
Richard Rajchel wrote on Sat, 09 February 2008 11:23

Once again I disagree. There is ALWAYS distortion present....not just when you over power a speaker.

In addition many horn loaded subs including the ones you mentioned will go pretty flat into the 30s.


Are you refering to horns the size as Lab Subs or boxes like EAW
LA 400?

For only large horn cabinets will reach down that low.

EAW LA 400 goes down to 45 Hertz in groups of 4. It won't extend any lower than that with great efficency because the horn is the limiting factor. Once the horn cuts off it refers back to the sealed chamber the woofer sits in to pick up where it leaves off. How many dbs down the frequency is will determine how efficent the box will be beyond the horn's cutoff point.

If the reflex is 0 dB Normalized Gain @ 40 Hertz, and the sealed chamber is - 10dB Normailzed Gain @ 40 Hertz, the reflex will be more efficent at 40 Hertz than the horn.

Quote:


You do need multiples to do it, but with the added efficiency of the horn you need less of them to reach a certain SPL that similar front loaded cabinets.


Yes. But at what frequency? What's the sense of having a lot of efficency if you do not need it at that particular frequency?

Quote:


It's not really trivial either. I highly efficient front loaded design may push 100 dB 1w/1 meter, but a highly efficient horn loaded design will be more like 106+ dB 1w/1 meter. Doubling power gains you 3dB so double once again to reach a 6dB increase.



I think we are looking at bass from a different point of view. For me Bass is 50 Hertz - down. Either design will achieve 106+ dB @ 1 watt, 1 meter if you are talking multiples. However, a
single Lab Sub is 45 Hertz. When you take into the consideration the size of the box, you can get a much lower frequency response
using two Mc Cauley 6174's in the same enclosure that will get you down in the mid 20's.

Quote:


You need 4 X the amount of front loaded enclosures to reach the output of 1 horn loaded design...of course these are just estimates. 4 LABs would probably crush 8 or 10 front loaded 18s at 1/2 the power or less...and in a group of 4 would go well into the 30s relatively flat.


If you take 8 Double Eighteens using the same dimensions as the Lab Sub. All housing Mc Cauley 6174 woofers, 4 Lab Subs will lose
when it gets down to the sub low frequencies.

There was Subwoofer Shootout held in 2007 in NYC. The two cabinets that offered the lowest extension was the Bassmaxx Trips
and Adire AD 618. Both were neck and neck in terms of frequency response. If you look at the dimensions among the two boxes 2 Trips takes up ruffly eight feet in width, whereas, two 618 takes up four. If you had the same amount AD 618s to equate to 8 feet the Trips would lose to the the 618s in overall SPL ranging from 100 - 35 Hertz.


Quote:


I'm not sure where you see horn loaded subs that roll off 10dB by 40Hz...i'd like to see those, or at least know what they are so I can avoid them when looking to upgrade my rig.


Horns requires a long mouth to get the desired frequency. They
also require a large mouth to deliver the frequency.


In order to have a true 40 Hertz horn, your going to need to have an overall mouth size of 8 feet high by 8 feet wide. You may get the proper length (Four 7 Foot Horns grouped together) but you'll never get a true 40 Hertz horn if the mouth isn't big enough.

So if you are looking at 8 Lab Subs, 8 Bassmaxx B Zero, or 8 of Wayne Parham's Horn designs your in pretty good shape. If you are looking at anything smaller it won't happen.

Best Regards,


Title: Re: front-loaded sub distortion
Post by: Ted Olausson on February 09, 2008, 08:02:18 am
Elliot Thompson wrote on Sat, 09 February 2008 11:31


All speakers are subjected to distortion if/when they are pushed beyond their limits.


No, speakers does SOFTLIMIT not HARDLIMIT (Unless you slam the coil in the bottom ofcourse).
Title: Re: front-loaded sub distortion
Post by: Elliot Thompson on February 09, 2008, 08:24:01 am
Richard Rajchel wrote on Sat, 09 February 2008 12:07

OK, enough is enough. You keep claiming that at -20dB or what ever power level you choose that there is no distortion. Well I went to Turbosounds website and procured Turbosound's own SPL Chart for the TSW-718. It's a front loaded double 18" subwoofer of pretty decent quality.

http://www.ubersales.com/images/frequency.gif

As you can see the 2nd harmonic and 3rd harmonic distortion are quite present at only 10% power.

Where are your magical no distortion subwoofers?



It's a bass bin.


That box is -4 dB @ 50 Hertz with 400 watt drivers in them.

Have you ever heard that box play? It resembles a very short straight horn and offers no sub bass. It's what my UK Friends would consider a "Kick Box."

I don't think I said there was no distortion. Bass is a form of
distortion. However, my explaination is more over reducing the distortion that is so common with those that tend to push everything beyond the woofer's and amplifier's limits.

Again. I'm refering to subs (50 Hz - down) not bass cabinets
(50 Hertz - up). Like I said in my previous post, our taste differs in bass.    

Best Regards,
Title: Re: front-loaded sub distortion
Post by: Elliot Thompson on February 09, 2008, 08:26:57 am
Ted Olausson wrote on Sat, 09 February 2008 13:02

Elliot Thompson wrote on Sat, 09 February 2008 11:31


All speakers are subjected to distortion if/when they are pushed beyond their limits.


No, speakers does SOFTLIMIT not HARDLIMIT (Unless you slam the coil in the bottom ofcourse).




The average user doesn't know anything about power compression in speakers. They just push it until it either rips to shreds or ketch on fire.  Laughing

Best Regards,
Title: Re: front-loaded sub distortion
Post by: Ted Olausson on February 09, 2008, 08:56:20 am
Elliot Thompson wrote on Sat, 09 February 2008 14:26

Ted Olausson wrote on Sat, 09 February 2008 13:02

Elliot Thompson wrote on Sat, 09 February 2008 11:31


All speakers are subjected to distortion if/when they are pushed beyond their limits.


No, speakers does SOFTLIMIT not HARDLIMIT (Unless you slam the coil in the bottom ofcourse).




The average user doesn't know anything about power compression in speakers. They just push it until it either rips to shreds or ketch on fire.  Laughing

Best Regards,


If they are that careless their wallet will soon tell them that something is wrong....

But, the coil vs magneticfield interaction and the suspension is nonlinear when you start to push the speaker, where that nonlinearity "starts" is different from speaker to speaker but it is always present to some degree.
Compare the suspension to a dog that is running around in the yard in a rubberband, it can move freely to some degree but as soon as the rubberband gets tensioned it can still move, but it cant move as effortlessly.
Even the air used in the box has nonlinear behaviour.
Title: Re: front-loaded sub distortion
Post by: Ian Hunt on February 09, 2008, 11:27:26 am
The average user probably would know what to do when confronted with a 'ketch on fire' but might be confused by 'waisted' wood. (Maybe thats why the ketch is aflame?)

But what the hell is a 'ruffly' sub, crinoline?

Thanks Elliot, if your audio knowledge matches your English you are precious!
Title: Re: front-loaded sub distortion
Post by: Andy Peters on February 09, 2008, 01:06:18 pm
Elliot Thompson wrote on Sat, 09 February 2008 03:31

Quote:


So what causes the distortion? Is it as simple as "overloading the box" in the sense that the output is clean up until some SPL level which essentially puts the system into saturation? Or is the distortion present at all levels? I am the first to admit that my knowledge of loudspeaker physics details is limited.

-a



Your assumptions about overloading the driver and/or amplifier is correct.


I'm assuming that the amplifier is not overloaded (running clean with headroom to spare). For this discussion, I'm interested in the cabinet and/or driver distortion.

I agree completely with your comments about not having enough Rig For The Gig.

-a
Title: Re: front-loaded sub distortion
Post by: Tim McCulloch on February 09, 2008, 02:08:37 pm
Ian-

Elliot is not a native of the continental US or UK.

I met him at the NYC sub shootout that Paul Bell sponsored @ Club Rebel.  Elliot has a good ear, catching some sonic performance issues the rest of us either overlooked or didn't hear at first.

You can read his impressions of the shootout in the Product Review forum, about a year ago.

Have fun, good luck.

Tim Mc
Title: Re: front-loaded sub distortion
Post by: Ian Hunt on February 09, 2008, 02:20:42 pm
Tim

I had realized that, and my post was not meant offensively! I have enjoyed Elliots creative use of language in this post rather a lot, and the flaming Ketch just tipped me over. I also understood exactly what he meant every time, but bringing a smile to my face needed appreciation.

Elliot, please continue  Smile
Title: Re: front-loaded sub distortion
Post by: Richard Rajchel on February 09, 2008, 05:40:38 pm
Elliot Thompson wrote on Sat, 09 February 2008 07:24



I don't think I said there was no distortion.


Elliot Thompson wrote on Sat, 09 February 2008 05:49



you shouldn't have any distortion from a reflex cabinet unless the distortion is coming the source.


This was my argument with you in the first place. Not about over powering subs, or whether a speaker is a bass bin, or kick box. Just the simple fact that harmonic distortion is present in all speakers....even at 10% power. I could care less where that Turbosound dropped off -4dB it had measured distortion throughout the range of it's intended use. It was only used for illustration purposes because Turbosound is one of the only Pro Audio companies to publish that information on their equipment.

I do, however, understand what you are saying about horns, and them unloading at a certain frequency. Why is that any different that an actual front loaded design if kept within a reasonable power limit?
Title: Re: front-loaded sub distortion
Post by: Pascal Pincosy on February 10, 2008, 01:08:46 am
Richard Rajchel wrote on Sat, 09 February 2008 14:40

Just the simple fact that harmonic distortion is present in all speakers....even at 10% power. I could care less where that Turbosound dropped off -4dB it had measured distortion throughout the range of it's intended use. It was only used for illustration purposes because Turbosound is one of the only Pro Audio companies to publish that information on their equipment.

I do, however, understand what you are saying about horns, and them unloading at a certain frequency. Why is that any different that an actual front loaded design if kept within a reasonable power limit?


All speakers have distortion produced by the driver, front or horn-loaded. A horn will also have some distortion inherent in the horn itself. One benefit of using a horn though, is that excursion is decreased. The greater the excursion, the higher the distortion. So driver distortion is decreased because the motor has more control over the cone.

If you want to have a very low distortion front-loaded system, you would use low excursion, low distortion drivers and you would not push them to full power, so you would have to bring a boat-load of speakers to every show. If you wanted a very low-distortion horn-loaded system, you would have to do the same. The difference is that the horn-loaded system would have increased sensitivity, so you would have more output for equal number of cabinets.
Title: Re: front-loaded sub distortion
Post by: Dave Rickard on February 10, 2008, 09:35:57 am
Elliot Thompson wrote on Sat, 09 February 2008 03:31

Quote:


So what causes the distortion? Is it as simple as "overloading the box" in the sense that the output is clean up until some SPL level which essentially puts the system into saturation? Or is the distortion present at all levels? I am the first to admit that my knowledge of loudspeaker physics details is limited.

-a



Your assumptions about overloading the driver and/or amplifier is correct.

Notice those that carry ample amount of subs/amplifiers never complain about distortion?

(snip)

All speakers are subjected to distortion if/when they are pushed beyond their limits. Whether you choose Horn-Loads or Reflex cabinets.




Elliot, I respect your chops, and I'm not sure you were referring to me.

I agree about "not enough rig for the gig", but in my anecdote, I was using low power sine waves, with plenty of headroom to spare. PLX 3002 on a single cab, in a 300 seat empty room.  When I played 40 Hz tones with the access door off, I could clearly hear 160Hz, as an overtone, and when I replaced the door I couldn't.

Actually, it was when I replaced the door that I noticed the LACK of 160Hz.  Then I took the door on and off a few times to compare.  I'm *not* saying it was ugly ,or prominent, or annoying, only that it was there.

Does anyone know what causes that?
Title: Re: front-loaded sub distortion
Post by: John Chiara on February 10, 2008, 02:47:55 pm
Richard Rajchel wrote on Fri, 08 February 2008 18:06


How do you think you can hear a low E on a bass guitar(41hz) on speakers that might be able to only go down to 100hz? It's harmonics that you hear. In my experience the lower the note the more prevalent the harmonics are. It's much easier to hear them with a low E on a bass than a high E on a guitar. That's just personal experience. I'm sure someone has a scientific explanation for that.

.


This is the concept that makes the Waves MaxxBass processors/plugins work..and it does work.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Alexander B Larsson on February 10, 2008, 03:01:03 pm
Back on topic... I have now realized we are actually comparing apples vs oranges if we compare many PA amps. I looked at the specs from a number of the the major brands, and I was actually quite surprised to see they are not using the same spec at all!  Confused
LAB and QSC clearly display all (?) relevant data, with the output power figures according to FTC (and even S/N ratio, that some manufacurers "forget").  Cool

EV shows the nice distorsion vs power graph of their P 3000, but no FTC power here (and I can not find any separate S/N figure)?

Crown XLS and MA also sports some "home brew" specs, with very little information. "1 kHz power"?

The Peavey figures ("hidden" deep in the owners manual of the amps) are also unclear - some kind of power "snapshot".
Rated power at 1 kHz at < 0,1% THD - but for what duty cycle?

I also checked the Digam 5000, which is only intended for 1 kHz?
It has no power bandwidth, no CMRR, no channel separation and distorsion figures that are mediocre at best...  Rolling Eyes

Some other (MI stuff) brands display even more interesting concepts of "music power", "peak output" etc, but that is not surprising to me.  Very Happy

However, with "big boys" like Harman Kardon, Peavey and EVI group not being very straightforward about power measurements, I don't know.  Rolling Eyes

To me, the openness about data is a very strong guide. I think I will focus on the LABs and some QSCs for my upcoming (small) purchase.

/Alexander from Sweden
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: John Roberts {JR} on February 10, 2008, 05:45:02 pm
Alexander B Larsson wrote on Sun, 10 February 2008 14:01

Back on topic... I have now realized we are actually comparing apples vs oranges if we compare many PA amps. I looked at the specs from a number of the the major brands, and I was actually quite surprised to see they are not using the same spec at all!  Confused
LAB and QSC clearly display all (?) relevant data, with the output power figures according to FTC (and even S/N ratio, that some manufacurers "forget").  Cool

EV shows the nice distorsion vs power graph of their P 3000, but no FTC power here (and I can not find any separate S/N figure)?

Crown XLS and MA also sports some "home brew" specs, with very little information. "1 kHz power"?

The Peavey figures ("hidden" deep in the owners manual of the amps) are also unclear - some kind of power "snapshot".
Rated power at 1 kHz at < 0,1% THD - but for what duty cycle?

I also checked the Digam 5000, which is only intended for 1 kHz?
It has no power bandwidth, no CMRR, no channel separation and distorsion figures that are mediocre at best...  Rolling Eyes

Some other (MI stuff) brands display even more interesting concepts of "music power", "peak output" etc, but that is not surprising to me.  Very Happy

However, with "big boys" like Harman Kardon, Peavey and EVI group not being very straightforward about power measurements, I don't know.  Rolling Eyes

To me, the openness about data is a very strong guide. I think I will focus on the LABs and some QSCs for my upcoming (small) purchase.

/Alexander from Sweden


Since I was actually the product manager for power amps at Peavey for a couple years I might be tempted to take your slight personally but I'm used to such accusations. It comes with being a successful high volume MI brand. I can't however suppress a defensive response.

Peavey makes a number of power amps for different markets and product categories so there will be different presentations of rated power generally dictated by specific market expectations. Guitar amps are routinely rated at several percent distortion while sound reinforcement or fixed install amps at much lower levels. The unifying dictate in amplifier specification is agency testing. UL has pretty strict regulations regarding how an amplifier can act when it's rated to drive a given load impedance to a rated power.

The FTC power spec you cite was a reaction to the wild west days of  hifi consumer amps when power specs were indeed fast and loose, and wildly inaccurate. While I certainly supported the standardization of what "watts" means (more or less), the 1/3rd power preconditioning requirement was actually overly strict for class AB hifi amps. That said, making consumers buy a little more aluminum than they need was a fair price to pay for standardized power ratings.

For professional power amps the 1/3rd power preconditioning is archaic and maybe even counter productive. Any engineer using class G/H topology will just dial in the mid power supply rail to run cool at 1/3rd power. Maybe optimal for real music, maybe not, it is surely optimal for passing FTC preconditioning.

We can all look longingly back at the good old days when 800W power amps put out 800 watts 24x7 but now that same 800W platform is pushing 1200W with the same heatsink and power transformer so you do the duty cycle math.

Perhaps ironic, one of those two companies you cite as the only honest players was the first, or one of the first, to market a lower cost, lower duty cycle amplifier series. While it was unquestionably a lower performance product, it was also lower cost and once the customers were given that option, the rest is history. All the other amp companies had to respond with similar models or give up market share to customers who were satisfied with that lower performance.

So not only have I seen an evolution from basically 8 ohm 24x7 power amps to 2 ohm power amps for hopefully long enough to get the job done. A second, yet lower performance option evolved with thermal circuit breakers instead of fuses to protect undersized power transformers, and the race to the bottom was on.

I would be very surprised to learn any major amplifier company who has been making power amplifiers for decades would intentionally game power specs, while I can't speak for specific merchandising in isolated markets. There will obviously be differences between models from even the same company as they fine tune price/performance to find market sweet spots.

Many consumers are downright ignorant about the inaudibility of small numerical differences between power points. So a marketer will be rewarded with sales for claiming a few extra watts here or there. I recall always budgeting in some spare  power since customers rarely had lab grade benches or loads and would often make inaccurate measurements.

Sorry if I'm rambling... Most (major) power amp companies provide specs in whatever format the majority of their customers want. In my experience Peavey  customers wanted specs that allowed them to make comparisons to other similar brands and models. I have no idea who's minding that store these days, and many models in current production were designed after my time so I have no idea how conservative the power specs are these days.

JR

PS:  Anyone familiar with my musings here knows I have long lobbied for a meaningful specification to characterize thermal capability or power output duty cycle.  There are many complexities associated with actually coming up with  an appropriate standard. There is already segmentation in the market between lower performance and higher performance designs, putting a number to it would create instant winners and losers in those market segments. Since the standard is somewhat arbitrary, I see little incentive for power amp companies to work together on this.


Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Ivan Beaver on February 10, 2008, 06:05:02 pm
Well stated!  I remember the old CS800 that you could run forever into just about any load and it would keep on going.  Very Happy

But the race to the bottom is not just in amplifiers, it goes through our entire industry.

Why does the XYZ 12"+ horn cost much more than the ABC version and yet the "specs" are just about the same.

Well listen to each and then turn them up loud and see what happens Laughing

There is a reason some products cost more than others, and it comes out in the overall performance, not just a few "specs" that are gathered in who know what manner.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Scott Smith on February 10, 2008, 06:33:05 pm
I still smile when I see my big stack of Peavey CS1200's and my CS800S, knowing I don't have to lug them anymore.  Despite their lower power ratings compared to today's amp, they sure had a nice punchy sound...if amps have a sound.   Very Happy
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: John Roberts {JR} on February 10, 2008, 06:56:31 pm
Scott Smith wrote on Sun, 10 February 2008 17:33

I still smile when I see my big stack of Peavey CS1200's and my CS800S, knowing I don't have to lug them anymore.  Despite their lower power ratings compared to today's amp, they sure had a nice punchy sound...if amps have a sound.   Very Happy


The CS1200 was one of the biggest class AB amps made... the distortion was very low and it has a robust power supply.

I still remember having to hump them around to set up for trade shows... CS1200x was something like 65# IIRC. The new modern stuff is sweet... That CS800S had a switcher so it was only 24# or so... but not much power by today's standards.

JR

Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Bob Leonard on February 10, 2008, 06:58:35 pm
John Roberts  {JR} wrote on Sun, 10 February 2008 17:45

Alexander B Larsson wrote on Sun, 10 February 2008 14:01

Back on topic... I have now realized we are actually comparing apples vs oranges if we compare many PA amps. I looked at the specs from a number of the the major brands, and I was actually quite surprised to see they are not using the same spec at all!  Confused
LAB and QSC clearly display all (?) relevant data, with the output power figures according to FTC (and even S/N ratio, that some manufacurers "forget").  Cool

EV shows the nice distorsion vs power graph of their P 3000, but no FTC power here (and I can not find any separate S/N figure)?

Crown XLS and MA also sports some "home brew" specs, with very little information. "1 kHz power"?

The Peavey figures ("hidden" deep in the owners manual of the amps) are also unclear - some kind of power "snapshot".
Rated power at 1 kHz at < 0,1% THD - but for what duty cycle?

I also checked the Digam 5000, which is only intended for 1 kHz?
It has no power bandwidth, no CMRR, no channel separation and distorsion figures that are mediocre at best...  Rolling Eyes

Some other (MI stuff) brands display even more interesting concepts of "music power", "peak output" etc, but that is not surprising to me.  Very Happy

However, with "big boys" like Harman Kardon, Peavey and EVI group not being very straightforward about power measurements, I don't know.  Rolling Eyes

To me, the openness about data is a very strong guide. I think I will focus on the LABs and some QSCs for my upcoming (small) purchase.

/Alexander from Sweden



The FTC power spec you cite was a reaction to the wild west days of  hifi consumer amps when power specs were indeed fast and loose, and wildly inaccurate. While I certainly supported the standardization of what "watts" means (more or less), the 1/3rd power preconditioning requirement was actually overly strict for class AB hifi amps. That said, making consumers buy a little more aluminum than they need was a fair price to pay for standardized power ratings.

For professional power amps the 1/3rd power preconditioning is archaic and maybe even counter productive. Any engineer using class G/H topology will just dial in the mid power supply rail to run cool at 1/3rd power. Maybe optimal for real music, maybe not, it is surely optimal for passing FTC preconditioning.

We can all look longingly back at the good old days when 800W power amps put out 800 watts 24x7 but now that same 800W platform is pushing 1200W with the same heatsink and power transformer so you do the duty cycle math.




Very well put John, but I might think not everyone remembers those days gone by.

I vote 90% power for 8 hours into a passive load. I remember a very well known and respected linear amplifier manufacturer whose advertisement was a skeleton holding down a morse key and the amp putting out CW @ 2KW. Obviously the operator died before the amp failed. I vote for that as well.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Scott Smith on February 10, 2008, 07:08:21 pm
JR, I have to laugh when I remember putting together my 1st BIG amp rack with 3 CS1200's, plus all the rest of the equipment.  I figured one rack would do it all.  It was acutally a radio transmitter rack.  I never considered or calculated the weight (I was much younger then).  Well, I couldn't pick it up.  I used it at one gig, and then dismantled it...lol.

I had one of the CS1200's apart to replace some transistors.  You're not kidding...more than 1/2 of the amp (and most of the weight) was the power supply.  Extemely robust!

That little CS800S did a very nice job keeping up with the bigger ones too.  I can't part with any of them to this day because of how well they performed... Smile  
Title: Re: Subwoofer amps - what are we REALLY hearing?Continuous ratings
Post by: Ivan Beaver on February 10, 2008, 07:11:54 pm
My standard test of day gone by was to put a sine wave in and look at the voltage at clip into both 8 and 4 ohms.  

That was the power rating, in my opinion.  At least it had to do it for a minute or so.

Many of todays "big power" amps cannot produce the rated wattage into rated impedance for a minute or more.  Usually rated in ms.

That may be good for peaks and all that is necessary, but is a far cry from the 'ol days where I used to let the amps "cook" for awhile with sine wave after a repair.

In fact, the factory test for a CS800 repair was to short the outputs with a 12ga wire and drive the amp into full DDT limiting untill the amp thermaled out and shut down.

Let it cool and see if it comes back to life (with the short removed).  If it does, then you did a good repair.  I was hesitant to do this hte first time, but after I found out it worked, it was my standard test for those amps-the few of them that I had to repair.  Built like a tank!

Say what you will about Peavey, but back in the day it was some of the most reliable stuff made.  I don't know about today as I am out of that market.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Ian Hunt on February 10, 2008, 07:25:14 pm
Application is the most important factor IMO

One company I worked for in the past got the task to convert large vibration tables (for shaking stuff till it broke) from ancient electric armature motors to 'voice coil' technology (allowing more complex patterns to be used) The amplifiers they designed had the biggest power supplies and most generous cooling I have ever seen.

An analogy that I always liked (oh no, auto's) is the formula one motor, 2.4 litres, atmospheric pressure and pump gas, 850hp is the result, so what's the catch? A life span of less than 2000 miles at competitive speeds. 19,000rpm in a V8 is still a tough engineering task. In years past when you could use unlimited (except by pocketbook) quantities  of engines 23,000 rpm and 1000hp was common. When turbo's were allowed BMW extracted 1700hp from a 1.5 litre 4 cylinder, they had a life span fractionally longer than the race, when they blew it was spectacular.

I expect my amps to last day in and day out, so be conservative with the ratings by all means.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Pascal Pincosy on February 11, 2008, 06:28:59 am
Alexander B Larsson wrote on Sun, 10 February 2008 12:01

I also checked the Digam 5000, which is only intended for 1 kHz?
It has no power bandwidth, no CMRR, no channel separation and distorsion figures that are mediocre at best...  Rolling Eyes


If you were interested in an amp from Powersoft, I'd suggest that you look at the K series amps. Powersoft hit the ball out of the park with that design. Those amps are on par or better than anything made by anyone.
Title: Re: Sound Is Subjective
Post by: Bob Lee (QSC) on February 12, 2008, 08:14:55 pm
Duncan McLennan wrote on Thu, 07 February 2008 17:20

I can easily tell the difference between both hi-fi amps and pro audio amps in my home system, even under blind test conditions.  I've done it many times.


It may be that the pro amps are more hi-fi than the "hi-fi" amps. Wink
Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 12, 2008, 08:28:16 pm
Bob Lee (QSC) wrote on Tue, 12 February 2008 19:14

Duncan McLennan wrote on Thu, 07 February 2008 17:20

I can easily tell the difference between both hi-fi amps and pro audio amps in my home system, even under blind test conditions.  I've done it many times.


It may be that the pro amps are more hi-fi than the "hi-fi" amps. Wink



I find, even in double blind listening tests, I can always pick out the one with a fan... at least on quiet passages.

JR
Title: Re: Subwoofer amps - what are we REALLY hearing?Continuous ratings
Post by: Lee Patzius on February 12, 2008, 08:48:34 pm
Ivan Beaver wrote on Sun, 10 February 2008 19:11

My standard test of day gone by was to put a sine wave in and look at the voltage at clip into both 8 and 4 ohms.  

That was the power rating, in my opinion.


F*cking-A right.

And THAT's the way it should be.

Real sine waves, reactive loads, and rate them in kVA, continuous.

Impulse ratings are a bunch of lies.








Edit: I mean sine waves (not sin waves).
Title: Re: Sound Is Subjective
Post by: Rob Spence on February 12, 2008, 09:41:49 pm
My DC300s don't have fans Smile
Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 12, 2008, 10:06:09 pm
Rob Spence wrote on Tue, 12 February 2008 20:41

My DC300s don't have fans Smile



Yeah, but the DC300 was quasi-complementary output stage, slower than rust...

Might actually hear that on a good system.

fast for DC tho....

JR
Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 13, 2008, 06:24:58 am
John Roberts  {JR} wrote on Wed, 13 February 2008 02:28

I find, even in double blind listening tests, I can always pick out the one with a fan... at least on quiet passages.



Run a speaker fullrange and you will be able to tell the difference with ease just by comparing the final bandwith.
-Unless you have trouble to hear the difference between 50Hz-400Hz compared to 16Hz-10KHz or 1Khz-12Khz compared to 200Hz-16Khz ofcourse...
Title: Re: Sound Is Subjective
Post by: Elliot Thompson on February 13, 2008, 06:47:14 am
Ted Olausson wrote on Wed, 13 February 2008 11:24

John Roberts  {JR} wrote on Wed, 13 February 2008 02:28

I find, even in double blind listening tests, I can always pick out the one with a fan... at least on quiet passages.



Run a speaker fullrange and you will be able to tell the difference with ease just by comparing the final bandwith.
-Unless you have trouble to hear the difference between 50Hz-400Hz compared to 16Hz-10KHz or 1Khz-12Khz compared to 200Hz-16Khz ofcourse...




Amplifiers are not the limiting factor. The loudspeaker is. What home audio woofers are you using capable in delivering 16 Hertz flat, without the aid of an eq?

Please post the TS Parameters so I can run it through one of my programs and see the results.

For the record all top of the line (In terms of series) pro amplifiers will go down into single digits as far as frequency bandwidth is concerned without shutting down. However, finding a Home Amplifier to do the same thing is a task in itself.

Best Regards,
Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 13, 2008, 07:27:28 am
Elliot Thompson wrote on Wed, 13 February 2008 12:47

Ted Olausson wrote on Wed, 13 February 2008 11:24

John Roberts  {JR} wrote on Wed, 13 February 2008 02:28

I find, even in double blind listening tests, I can always pick out the one with a fan... at least on quiet passages.



Run a speaker fullrange and you will be able to tell the difference with ease just by comparing the final bandwith.
-Unless you have trouble to hear the difference between 50Hz-400Hz compared to 16Hz-10KHz or 1Khz-12Khz compared to 200Hz-16Khz ofcourse...




Amplifiers are not the limiting factor. The loudspeaker is. What home audio woofers are you using capable in delivering 16 Hertz flat, without the aid of an eq?

Please post the TS Parameters so I can run it through one of my programs and see the results.

For the record all top of the line (In terms of series) pro amplifiers will go down into single digits as far as frequency bandwidth is concerned without shutting down. However, finding a Home Amplifier to do the same thing is a task in itself.

Best Regards,


No home device can deliver that low what i know of.(Atleast my clockradio cant do that and that is the only homedevice i have seen in 20 years...)
-If you wanna see it you have to come to my warehouse and listen for yourself, unless you try it yourself first.

BTW:
How did you intend to simulate different amps in a simulationprogram?????
-Thats the important point, it is clearly audible but how does it work????

BTW2:
The possibility to create 16Hz is a function of my small officespace, look at the different horns response in the midrange  instead, 400Hz vs 10KHz or 200Hz vs 1Khz.
Title: Re: Sound Is Subjective
Post by: Elliot Thompson on February 13, 2008, 08:35:24 am
Ted Olausson wrote on Wed, 13 February 2008 12:27

Elliot Thompson wrote on Wed, 13 February 2008 12:47

Ted Olausson wrote on Wed, 13 February 2008 11:24

John Roberts  {JR} wrote on Wed, 13 February 2008 02:28

I find, even in double blind listening tests, I can always pick out the one with a fan... at least on quiet passages.



Run a speaker fullrange and you will be able to tell the difference with ease just by comparing the final bandwith.
-Unless you have trouble to hear the difference between 50Hz-400Hz compared to 16Hz-10KHz or 1Khz-12Khz compared to 200Hz-16Khz ofcourse...




Amplifiers are not the limiting factor. The loudspeaker is. What home audio woofers are you using capable in delivering 16 Hertz flat, without the aid of an eq?

Please post the TS Parameters so I can run it through one of my programs and see the results.

For the record all top of the line (In terms of series) pro amplifiers will go down into single digits as far as frequency bandwidth is concerned without shutting down. However, finding a Home Amplifier to do the same thing is a task in itself.

Best Regards,


No home device can deliver that low what i know of.(Atleast my clockradio cant do that and that is the only homedevice i have seen in 20 years...)
-If you wanna see it you have to come to my warehouse and listen for yourself, unless you try it yourself first.

BTW:
How did you intend to simulate different amps in a simulationprogram?????
-Thats the running point, it is clearly audible but how does it work????



I wasn't planning on simulating different amps with a program.

You mentioned 16 Hertz and, I was commenting on what speaker you've found that can reproduce 16 Hertz flat without the aid of an Equalizer. Many tend to state these lower than average response and don't take into account the processing (Eq, Bandpass filters, coupling with the walls in the room) to achieve such a fete. All of that changes when your only boundary is the ground it sits on when doing outside events.

It is very easy for me to simulate the frequency response of the driver using a loudspeaker design program and see if indeed
the woofer can deliver 16 Hertz, 0 dB Normalized gain. This is why, I requested the TS paramaters of the driver.

As for the amplifiers, all you need is the documentation from the manufacter to see what is the lowest frequency the amplifier will produce before it: 1. Begins to rolloff or 2. Activates it's protection cicuitry.

Rob Spence mentioned the DC 300 which, frequency bandwidth is flat down to 1 Hertz. So, it will have no issues delivering 16 Hertz. However, finding a woofer that can withstand 16 Hertz with a sizable amount of output (Considering the human hearing is very insensitive in terms of low frequency) so we can enjoy it, is not as easy as one may assume.

Best Regards,
Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 13, 2008, 09:44:25 am
Elliot Thompson wrote on Wed, 13 February 2008 14:35


I wasn't planning on simulating different amps with a program.

You mentioned 16 Hertz and, I was commenting on what speaker you've found that can reproduce 16 Hertz flat without the aid of an Equalizer. Many tend to state these lower than average response and don't take into account the processing (Eq, Bandpass filters, coupling with the walls in the room) to achieve such a fete. All of that changes when your only boundary is the ground it sits on when doing outside events.

It is very easy for me to simulate the frequency response of the driver using a loudspeaker design program and see if indeed
the woofer can deliver 16 Hertz, 0 dB Normalized gain. This is why, I requested the TS paramaters of the driver.



If you werent planning to simulare the SAME speaker with different amps then the simulation is useless....
I can get get different response from DIFFERENT speakers too and there is nothing strange with that...

I also said in the message that is was best to focus on the change in midrange. AND that those 16Hz was a result of  roomboundaries in the testenviroment.

The only differnce is the amp, same room/placement, same speakers, same tonegenerator. (For measuring 16Hz a microphone+smaart were used) Even the same cables were used...

Quote:


As for the amplifiers, all you need is the documentation from the manufacter to see what is the lowest frequency the amplifier will produce before it: 1. Begins to rolloff or 2. Activates it's protection cicuitry.



So, what specifications from the amplifiermanual can explain a hicutoff at 400Hz versus 10Khz or the locut at 200Hz versus 1Khz???? Since both amps clearly can deliver those frequencies.

Quote:


Rob Spence mentioned the DC 300 which, frequency bandwidth is flat down to 1 Hertz. So, it will have no issues delivering 16 Hertz. However, finding a woofer that can withstand 16 Hertz with a sizable amount of output (Considering the human hearing is very insensitive in terms of low frequency) so we can enjoy it, is not as easy as one may assume.



I am well aware of how the ear works in general, the 50ms window, the integration of related sounds in packages and so forth.
Sure i want to know more about how distortion is related to percieved loudness
(Read this text which notes the relationship between percieved SPL and distortion as opposed to measured SPL , but you will probably not know what it is unless you have experienced the phenomen yourself...
http://www.moultonlabs.com/more/power_amps_revisited/ )

But that is far from the basic information about how SPL A,B,C,X weighting works and why it exists...

Title: Re: Sound Is Subjective
Post by: Elliot Thompson on February 13, 2008, 10:25:05 am
Ted Olausson wrote on Wed, 13 February 2008 14:44



If you werent planning to simulare the SAME speaker with different amps then the simulation is useless....
I can get get different response from DIFFERENT speakers too and there is nothing strange with that...




So why don't you post the TS Parameters of the woofers in question. I do own Crown Macrotech, QSC Powerlight, and Crest Professional so it's not a matter of listening to the charcteristics from various woofers. I've done that many of times
with numerous brands of woofers.

The driver needs to meet my standards. If the the driver can't deliver the goods no amount of swapping of amplifiers is going to make it deliver what it is not designed to do. The co-relation between the woofer and cabinet is more vital than switching amplifiers.  

Quote:


I also said in the message that is was best to focus on the change in midrange. AND that those 16Hz was a result of  roomboundaries in the testenviroment.


My appologies. I didn't notice that. So, what are the drivers in
question you've drawn to this conclusion. I am refering to raw components.

Quote:


The only differnce is the amp, same room/placement, same speakers, same tonegenerator. (For measuring 16Hz a microphone+smaart were used) Even the same cables were used...



Why not test it outdoors so you can eliminate the room and see if the conclusions are the same?


Quote:


So, what specifications from the amplifiermanual can explain a hicutoff at 400Hz versus 10Khz or the locut at 200Hz versus 1Khz???? Since both amps clearly can deliver those frequencies.


What amplifier (Model number) are you refering to? And did you take the frequency response of the box into question?

You'll need to get your hands on the Service Manual to find out what you are searching for. The user Manual won't go into great detail for the average user doesn't need that type of information.


I will read the link you provided a little later (I'm in class as I type) and, check back later tonight on your reply.

Best Regards,
Title: Re: Sound Is Subjective
Post by: Bob Lee (QSC) on February 13, 2008, 11:41:55 am
Difference in what? The amplifiers?
Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 14, 2008, 10:34:54 am
Elliot Thompson wrote on Wed, 13 February 2008 16:25


Why not test it outdoors so you can eliminate the room and see if the conclusions are the same?



No, this is totally  irrelevant.


Quote:


You'll need to get your hands on the Service Manual to find out what you are searching for. The user Manual won't go into great detail for the average user doesn't need that type of information.



( The usermanual for my old Sony U-Matic editing system (9600?) had almost only servicerelated information in it, so it is not possible to make that distinction. )

I have tried resistors up to 100ohm on the cable and there are no difference at all, so DF is out of the question. Otherwise changes in DF between 0-15 is as you know, well known to change the box FR.(Less DF more bass more DF less bass)

BTW how can an amp that is stated to have 1000w/8ohm and 1100w/4ohm at 0% distortion hade a DF above 1000!? It should be 1000/2000/4000 watt at 8/4/2 ohm...

Well, i am very tired now, have been working all night, but could it be so simple as throatphase versus amplifierphase?
Title: Re: Sound Is Subjective
Post by: Bob Lee (QSC) on February 14, 2008, 12:13:03 pm
Ted Olausson wrote on Thu, 14 February 2008 07:34


BTW how can an amp that is stated to have 1000w/8ohm and 1100w/4ohm at 0% distortion hade a DF above 1000!? It should be 1000/2000/4000 watt at 8/4/2 ohm...


???

Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 14, 2008, 12:15:37 pm
Ted Olausson wrote on Thu, 14 February 2008 09:34




BTW how can an amp that is stated to have 1000w/8ohm and 1100w/4ohm at 0% distortion hade a DF above 1000!? It should be 1000/2000/4000 watt at 8/4/2 ohm...




I understand the logic behind your misunderstanding but it assumes unlimited current capability in the amplifier. Amplifier DF is related to output impedance which is strictly a matter of device characteristics, internal wiring, and negative feedback, or more specifically loop gain margin. An amplifier's maximum power at lower load impedances, is dominated by current capability and only in the margin to source impedance related output stage losses.  An amplifier's close but not perfect doubling, suggest source impedance effects. Wider divergence from 2x per halving is caused by PS or protection circuitry current limiting output stage.

In an ideal world, there would be a strict doubling of power with halving of load impedance but in practice this requires delivering 4x the amp at 2 ohms as for 8 ohms. Customers have routinely voted with their purchases to support a lesser capability, The marketplace provides what customers are willing to pay for.

JR



Title: Re: Sound Is Subjective
Post by: Rob Spence on February 14, 2008, 12:28:50 pm
This is the LF driver I have connected to my DC300 Smile
It is mounted to drive into a sealed enclosure (that is, basket side out).

Driver     Fs     Qts     Qes     Qms     Vas     Re     Prated     Xmax     Diam
L12P48    19.5    0.4    0.44    10    9.52    5    150    0.22    12

Note, I don't claim to understand these parameters and didn't choose them. The speaker cabinet maker did that.
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Tim Duffin on February 15, 2008, 09:22:02 pm
That is not what I was talking about.  A class C "Amplifier" in the sense I am familar is used for unidirectional excitation of particles in water. I think about gyrators for ultrasonic cleaning while you are thinking of gyrators for RF... I never even knew that they had a circuit called a 'gyrator' in RF.  

I remember having to assemble a class-c amp in college and look at its output on a scope-- looked like a bunch of humps with some overshoot at zero crossing.  

T
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: John Roberts {JR} on February 15, 2008, 10:23:34 pm
Tim Duffin wrote on Fri, 15 February 2008 20:22

That is not what I was talking about.  A class C "Amplifier" in the sense I am familar is used for unidirectional excitation of particles in water. I think about gyrators for ultrasonic cleaning while you are thinking of gyrators for RF... I never even knew that they had a circuit called a 'gyrator' in RF.  

I remember having to assemble a class-c amp in college and look at its output on a scope-- looked like a bunch of humps with some overshoot at zero crossing.  

T


A gyrator is an active circuit to synthesize an inductor from resistor, capacitor, and a gain stage. A gyrator could be operated at RF frequencies.

Class C is a resonant amplifier circuit commonly used in RF.

It is you who seems to be confusing the two in your post here .   http://srforums.prosoundweb.com/index.php/m/290789/30842/0// /361/#msg_290789

Tim Duffin wrote on Thu, 07 February 2008 20:09


Fine, Ill use the quote button.

Anyways, the correct answer for my question you did not get. The circuit which is class C is called a "gyrator" and it is not used in audio as per JR's comment.




FWIW, what the output of a class C amp looks like will depend on the rep rate it is excited at.. it could look sinusoidal if excited synchronously with it's resonance. If hit with an impulse it will look like a damped ring .  

I am not familiar with your "unidirectional excitation of particles in water" perhaps a pump? Gyrators and Class C have two pretty well defined and unrelated meanings in audio.

I don't doubt there are sundry other devices called gyrators.

for example

Rush developed a variation of this spinning approach called the Gyrator, a horizontal board on which torpid patients were strapped and spun to stimulate blood circulation. (1) An Irish physician developed his own version of this twirling device: O'Halloran's swing (figure 3). Patients were rotated up to 100 times a minute in it. The centrifugal force drove blood to the brain, theoretically treating mental illness and gaining patient obedience. (5)


Laughing

JR



Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 16, 2008, 09:53:45 am
John Roberts  {JR} wrote on Thu, 14 February 2008 18:15


I understand the logic behind your misunderstanding but it assumes unlimited current capability in the amplifier. Amplifier DF is related to output impedance which is strictly a matter of device characteristics, internal wiring, and negative feedback, or more specifically loop gain margin. An amplifier's maximum power at lower load impedances, is dominated by current capability and only in the margin to source impedance related output stage losses.  An amplifier's close but not perfect doubling, suggest source impedance effects. Wider divergence from 2x per halving is caused by PS or protection circuitry current limiting output stage.

In an ideal world, there would be a strict doubling of power with halving of load impedance but in practice this requires delivering 4x the amp at 2 ohms as for 8 ohms. Customers have routinely voted with their purchases to support a lesser capability, The marketplace provides what customers are willing to pay for.




Sorry, i was tired. OPAMPS has the same behaviour.
But what other (Known or suspected) factors except DF has a great impact on the relationship between speaker and amp?
Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 16, 2008, 10:06:30 am
Ted Olausson wrote on Sat, 16 February 2008 08:53



Sorry, i was tired. OPAMPS has the same behaviour.
But what other (Known or suspected) factors except DF has a great impact on the relationship between speaker and amp?



I am very much a proponent of amplifiers sounding quite similar to each other as long as operated linearly.

Besides voltage clipping which is more common than many operators suspect, there is running out of current. Especially for an amplifier that doesn't follow the approximate doubling of power with halving the load impedance. That amplifier will current clip before it voltage clips at low impedance loads.

Another poorly understood factor is how loudspeakers, especially when using passive crossovers vary their impedance with frequency. Impedance dips with paralleled speakers could drop quite low at spot frequencies.

The most audible differences are frequency response errors, and added signals (distortion). The tiny differences between amplifiers operating linearly are IMO insignificant in the context of the loudspeakers they are connected too, and room modes, and sources like microphones.

JR
Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 17, 2008, 08:50:48 am
John Roberts  {JR} wrote on Sat, 16 February 2008 16:06


I am very much a proponent of amplifiers sounding quite similar to each other as long as operated linearly.

Besides voltage clipping which is more common than many operators suspect, there is running out of current. Especially for an amplifier that doesn't follow the approximate doubling of power with halving the load impedance. That amplifier will current clip before it voltage clips at low impedance loads.



Now we are getting somewhere....
But as you say, the linear area doesnt go all the way to clip, it will deviate much earlier than that. Especially with amplifiers with small PSUs and speakers with high levels of back EMF.

Quote:


Another poorly understood factor is how loudspeakers, especially when using passive crossovers vary their impedance with frequency. Impedance dips with paralleled speakers could drop quite low at spot frequencies.



That is close to one of the secrets behind the mystical speakers i was mentioning...
Their Re is 5.2 but their Z is 11 ohm within their BW.
(One of the amps is also very close to "2xpower" from DC to 80MHz and has perfect stepresponse, the other is a normal amp)

Quote:


The most audible differences are frequency response errors, and added signals (distortion). The tiny differences between amplifiers operating linearly are IMO insignificant in the context of the loudspeakers they are connected too, and room modes, and sources like microphones.



So are the differences between preamps....

However, the speakers electrical Q is made by the amp, and when you let Qes change then FR also changes.
-and so does the stepresponse.

Protection will also affect the sound much earlier than expected, a perfect example of that is QSC EX vs MXa which is the same amp with different protection, and there is a big difference between them even at -20dB.
There is also a numbergame with distortion, THD% is very inaudible but IM% is almost never stated but highly audible.

BTW, i am not saying that amps are important in comparision to other elements, i am just saying that amps arent perfect.

Title: Re: Sound Is Subjective
Post by: Andy Peters on February 17, 2008, 01:57:05 pm
Ted Olausson wrote on Sun, 17 February 2008 06:50

(One of the amps is also very close to "2xpower" from DC to 80MHz and has perfect stepresponse, the other is a normal amp)


80 MEGAHERTZ?

Why does it need bandwidth out that far, if it's an audio amplifier?

-a
Title: Well, some companies display IM distorsion...
Post by: Alexander B Larsson on February 18, 2008, 06:01:46 am
Ted Olausson said:
"There is also a numbergame with distortion, THD% is very inaudible but IM% is almost never stated but highly audible."

Well, Labgruppen and QSC certainly displays figures for IM distorsion, at least for the amp models I checked.
Coincidence?  Rolling Eyes

I DO find it interesting that many of the posters really liked the sound and reliability of the "old, continous power, 24/7" amps. Many of you have also clearly said that you ARE willing to compromise on the bass accuracy to get more power and lighter racks.

And I think nobody argues that the D class technology is still in need of more development, since the IM and load matching issues are still not really solved...

/Alexander
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Dan Bouchard on February 18, 2008, 08:10:13 am
Duncan McLennan wrote on Tue, 05 February 2008 11:22

I've personally always like amplifiers with real toroidal transformers and linear power supplies.  Switching amps, although convenient for weight purposes, have never sounded as good to my ear.  That might be just me.

So is weight worth sacrificing sound quality?  I don't know.


I am 100% with you on this, nothing sounds as good as my Crest Pro9001, my 9200 come really close but its not the same animal
Title: Re: Well, some companies display IM distorsion...
Post by: John Roberts {JR} on February 18, 2008, 10:32:22 am
Alexander B Larsson wrote on Mon, 18 February 2008 05:01

Ted Olausson said:
"There is also a numbergame with distortion, THD% is very inaudible but IM% is almost never stated but highly audible."

Well, Labgruppen and QSC certainly displays figures for IM distorsion, at least for the amp models I checked.
Coincidence?  Rolling Eyes

I DO find it interesting that many of the posters really liked the sound and reliability of the "old, continous power, 24/7" amps. Many of you have also clearly said that you ARE willing to compromise on the bass accuracy to get more power and lighter racks.

And I think nobody argues that the D class technology is still in need of more development, since the IM and load matching issues are still not really solved...

/Alexander


THD+N is kind of a kitchen sink measurement of all nonlinearity, noise, or deviation from straight wire with gain performance, IMD is a specific variant of distortion. Both can be audible depending on amount and masking capability of program material.  People are often confused about THD specifications and use of THD as a qualifier for power measurements (wrt clipping).

I expect class D to continue developing. It has some unique performance limitations but AFAIK IMD is not inherent to class D topology, and load interaction with output filters is a well understood engineering trade off to amp designers. I find it remarkable that modern class D amps with DSP on board don't apply that technology to mitigate the output filter losses (mostly simple freq response error).

JR

Title: Re: Well, some companies display IM distorsion...
Post by: Alexander B Larsson on February 18, 2008, 11:17:45 am
Well John, I mean exactly what I wrote...  Very Happy
Apart from THD figures, Labgruppen and QSC also displays separate Intermodulation distorsion measurement figures, be it SMPTE or DIM 30.  Smile

Regarding the class D, was I mostly thinking of the inherent "coloration" in the higher frequencies, and the problems to get rid of that kind of topology related issues.
But the amps sure are light and use the supplied outlet power in a very efficient way - just what many here ask for!  Smile

/Alexander
Title: Re: Well, some companies display IM distorsion...
Post by: Duncan McLennan on February 18, 2008, 11:41:24 am
Not all class D amps are light, only those with a switching power supply would be as light as something like a PLX.

I have a whole rack of Crest CD, which are class D and have toroidal transformers.  They're about 40lbs a piece, and sound pretty darn good.  They're extremely efficient.  500w/side at 4Ω and they draw something like 4A at 1/3 power.  I put four on a 20A circuit.

And they sound pretty darn good too.  I actually took one home, threw it in my stereo, and A/B'ed it with some of the good, and not s good hi-fi amps I've got lying around.  I also tested an old Microtech, and a Yorkville Audiopro, and a PLX.  I was surprised, the the Yorkville was the most 'musical' sounding of the whole lot.  The Microtech had tons of balls, but really no finesse.  The PLX sounded like a tin can, and the Crest-CD felt fairly well balanced compared to the rest.  Closest to the Yorkie in terms of tone.
Title: Re: Well, some companies display IM distorsion...
Post by: John Roberts {JR} on February 18, 2008, 04:11:30 pm
Alexander B Larsson wrote on Mon, 18 February 2008 10:17

Well John, I mean exactly what I wrote...  Very Happy
Apart from THD figures, Labgruppen and QSC also displays separate Intermodulation distorsion measurement figures, be it SMPTE or DIM 30.  Smile

Regarding the class D, was I mostly thinking of the inherent "coloration" in the higher frequencies, and the problems to get rid of that kind of topology related issues.
But the amps sure are light and use the supplied outlet power in a very efficient way - just what many here ask for!  Smile

/Alexander


I was responding more to your comment

" And I think nobody argues that the D class technology is still in need of more development, since the IM and load matching issues are still not really solved...

/Alexander "


Class D technology has been around for decades and while anything can be refined, the primary developments these days is related to device technology. Higher voltage and current switching devices is what allows the formidable power output from newer class D amps.

A consequence of this higher output current is bigger/heavier output filters, which one recent model seems to have scrimped on to save size, or weight, or cost, or whatever.  I am not aware of any inherent  IM or load matching issues, while output impedance is a design consideration to be managed.

In light of the at least one model I mentioned it is prudent to look at top octave frequency response when driving low impedance HF drivers. Since this looks like a one pole LPF, corrective EQ should restore amplitude and phase response.

JR
Title: Re: Sound Is Subjective
Post by: Bob Leonard on February 18, 2008, 06:01:39 pm
Andy Peters wrote on Sun, 17 February 2008 13:57

Ted Olausson wrote on Sun, 17 February 2008 06:50

(One of the amps is also very close to "2xpower" from DC to 80MHz and has perfect stepresponse, the other is a normal amp)


80 MEGAHERTZ?

Why does it need bandwidth out that far, if it's an audio amplifier?

-a


It won't and it can't. Well maybe, but it would be one hell of a circuit. Think of the possabilities. Audio through the RF spectrum with one amplifier. 80mhz is above most military radio frequencies. Look up BPL and tell me what you
find.
Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 18, 2008, 06:32:46 pm
Bob Leonard wrote on Mon, 18 February 2008 17:01

Andy Peters wrote on Sun, 17 February 2008 13:57

Ted Olausson wrote on Sun, 17 February 2008 06:50

(One of the amps is also very close to "2xpower" from DC to 80MHz and has perfect stepresponse, the other is a normal amp)


80 MEGAHERTZ?

Why does it need bandwidth out that far, if it's an audio amplifier?

-a


It won't and it can't. Well maybe, but it would be one hell of a circuit. Think of the possabilities. Audio through the RF spectrum with one amplifier. 80mhz is above most military radio frequencies. Look up BPL and tell me what you
find.


The name of the company escapes me now, but there was an amp company back in the late '70s or early '80s whose claim to fame was strip line (?)  technology and Mhz bandwidth, I doubt even they were pushing 80 Mhz power bandwidth but they were faster than your average Fender...

Needless to say there was no "there" there and they faded into oblivion. Something about "you can't fool all the people all the time..." (without a huge marketing budget).

JR

 
Title: Re: Sound Is Subjective
Post by: Mac Kerr on February 18, 2008, 06:41:19 pm
John Roberts  {JR} wrote on Mon, 18 February 2008 18:32

The name of the company escapes me now, but there was an amp company back in the late '70s or early '80s whose claim to fame was strip line (?)  technology and Mhz bandwidth, I doubt even they were pushing 80 Mhz power bandwidth but they were faster than your average Fender...

Needless to say there was no "there" there and they faded into oblivion. Something about "you can't fool all the people all the time..." (without a huge marketing budget).
 
I don't know if it's what you were thinking of, but that was a claim to fame of Spectrasonics amps. The Spectrasonics 700 was a 70W amp on a card. You could load up to 8 of them in the card cage. they were very sensitive to wiring issues, I smoked a cage full of them when they went into ultrasonic oscillation because there was a grounding issue.

Mac
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Tim McCulloch on February 18, 2008, 06:42:01 pm
Can we stick a fork in this thread?  It's done....

Tim Mc
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Mac Kerr on February 18, 2008, 06:43:32 pm
Tim McCulloch wrote on Mon, 18 February 2008 18:42

Can we stick a fork in this thread?  It's done....

Tim Mc
It was done on day one.

Mac
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Tim McCulloch on February 18, 2008, 06:47:13 pm
Mac Kerr wrote on Mon, 18 February 2008 17:43

Tim McCulloch wrote on Mon, 18 February 2008 18:42

Can we stick a fork in this thread?  It's done....

Tim Mc
It was done on day one.

Mac


Hmmmm... Let's carve it up and serve it...  lots of tofu; most of the real meat went unnoticed.

Tim Mc
Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 18, 2008, 07:03:42 pm
Mac Kerr wrote on Mon, 18 February 2008 17:41

I don't know if it's what you were thinking of, but that was a claim to fame of Spectrasonics amps. The Spectrasonics 700 was a 70W amp on a card. You could load up to 8 of them in the card cage. they were very sensitive to wiring issues, I smoked a cage full of them when they went into ultrasonic oscillation because there was a grounding issue.

Mac



No not Spectrasonics.. they were around for quite a while IIRC.. The amp company I had in mind was a flash in the pan, didn't last more than a year or two...

WRT the Spectra's I was always nervous about running power amp power et al through PCB edge connectors, but people liked the modularity.

JR

Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 18, 2008, 07:37:04 pm
Andy Peters wrote on Sun, 17 February 2008 19:57

Ted Olausson wrote on Sun, 17 February 2008 06:50

(One of the amps is also very close to "2xpower" from DC to 80MHz and has perfect stepresponse, the other is a normal amp)


80 MEGAHERTZ?

Why does it need bandwidth out that far, if it's an audio amplifier?

-a


No, typo, 80 KILO hertz is it bandlimited to.
It can only handle 300KHz at full power, but the risetime is 0,5uS and slewrate is 180v/uS.

Should i mention the brand!? Naah Twisted Evil
Title: Re: Sound Is Subjective
Post by: Andy Peters on February 18, 2008, 07:52:28 pm
Ted Olausson wrote on Mon, 18 February 2008 17:37

Andy Peters wrote on Sun, 17 February 2008 19:57

Ted Olausson wrote on Sun, 17 February 2008 06:50

(One of the amps is also very close to "2xpower" from DC to 80MHz and has perfect stepresponse, the other is a normal amp)


80 MEGAHERTZ?

Why does it need bandwidth out that far, if it's an audio amplifier?

-a


No, typo, 80 KILO hertz is it bandlimited to.


And this is EXACTLY why I'm a pedantic asshole.

There is a significant difference between 80 MHz and kHz. (And if anyone writes mHz, that's a very small bandwidth.) So, at least proofread before posting. (And yes, I expect to be called on my typos, and I always admit to making mistakes.)

Anyways -- I'm not significantly impressed by 80 kHz bandwidth.

-a
Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 18, 2008, 08:11:51 pm
Andy Peters wrote on Tue, 19 February 2008 01:52


And this is EXACTLY why I'm a pedantic asshole.

There is a significant difference between 80 MHz and kHz. (And if anyone writes mHz, that's a very small bandwidth.) So, at least proofread before posting. (And yes, I expect to be called on my typos, and I always admit to making mistakes.)

Anyways -- I'm not significantly impressed by 80 kHz bandwidth.

-a


It is easy to remove the 80KHzfilter, its just a cap and a resistor on the input but i dont expect it to do any difference.
Title: Re: Sound Is Subjective
Post by: Andy Peters on February 18, 2008, 08:14:25 pm
Ted Olausson wrote on Mon, 18 February 2008 18:11

Andy Peters wrote on Tue, 19 February 2008 01:52


And this is EXACTLY why I'm a pedantic asshole.

There is a significant difference between 80 MHz and kHz. (And if anyone writes mHz, that's a very small bandwidth.) So, at least proofread before posting. (And yes, I expect to be called on my typos, and I always admit to making mistakes.)

Anyways -- I'm not significantly impressed by 80 kHz bandwidth.

-a


It is easy to remove the 80KHzfilter, its just a cap and a resistor on the input but i dont expect it to do any difference.


OK, smart guy, why not try it -- remove the filter and see how long the amp lasts before ultrasonic oscillation destroys the output stage.

-a

PS: it's kHz, not KHz. K is absolute temperature in Kelvin. Kower-case k is kilo-.
Title: Re: Sound Is Subjective
Post by: Mac Kerr on February 18, 2008, 08:18:08 pm
Andy Peters wrote on Mon, 18 February 2008 20:14

PS: it's kHz, not KHz. K is absolute temperature in Kelvin. Kower-case k is kilo-.
Oh Andy, you pedant you.  Laughing

Mac

Title: Re: Sound Is Subjective
Post by: Ted Olausson on February 18, 2008, 08:20:46 pm
Andy Peters wrote on Tue, 19 February 2008 02:14


OK, smart guy, why not try it -- remove the filter and see how long the amp lasts before ultrasonic oscillation destroys the output stage.


What does inputcap have to do with oscilliation!? it is a inputbuffer after the cap...
-If so, it would oscilliate when there wasnt any connector in the amp....
Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 18, 2008, 08:22:16 pm
Ted Olausson wrote on Mon, 18 February 2008 18:37



No, typo, 80 KILO hertz is it bandlimited to.
It can only handle 300KHz at full power, but the risetime is 0,5uS and slewrate is 180v/uS.

Should i mention the brand!? Naah Twisted Evil


Well that doesn't exactly clear it up for me... Band limited to 80 kHz but only handles 300 kHz at full power. Is that another typo?

I am an advocate of rise time instead of slew rate specifications. For the record the rise time spec implies a low pass filter either before or incorporated into the input gain stage. The few times I've seen rise specs for power amps there is often a foot note that the rise time filter is disabled during the slew rate measurement. Because customers insist on hearing high slew rate numbers in a "more is better" contest despite having little clue about what they actually mean. Another archaic specification that used to mean something when amps were slow.

Since slew limiting is like clipping in the time domain, a properly low passed amp can't be slew limited with a valid input signal, making such measurements a little difficult. A max slew rate could be imputed from the power bandwidth frequency and voltage, but a well designed circuit is typically faster than that.

If the power bandwidth really is 300 kHz that is excessive for audio reproduction.  

My only possible interest in the brand name is to look up a data sheet and see what the specs really are, but nah..  Twisted Evil  

JR


Title: Re: Sound Is Subjective
Post by: SteveKirby on February 18, 2008, 08:40:47 pm
John Roberts  {JR} wrote on Mon, 18 February 2008 17:32

The name of the company escapes me now, but there was an amp company back in the late '70s or early '80s whose claim to fame was strip line (?)  technology and Mhz bandwidth, I doubt even they were pushing 80 Mhz power bandwidth but they were faster than your average Fender...

Needless to say there was no "there" there and they faded into oblivion. Something about "you can't fool all the people all the time..." (without a huge marketing budget).

JR

 

Are you thinking of Spectral?  I think they were based in SF and founded on the premise that bandlimiting to 20kHz created slew limiting bluring time base information that provided directional cues.
There was an arm of the company that made records,  Reference Recordings.  I have one record of theirs with Stephen Gordon playing Chopin.  Lots of ambience that sounds like the rear third of the hall.
Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 18, 2008, 08:52:15 pm
Ted Olausson wrote on Mon, 18 February 2008 19:20



What does inputcap have to do with oscilliation!? it is a inputbuffer after the cap...
-If so, it would oscilliate when there wasnt any connector in the amp....


Agreed.. an input rise time filter's only function is to harmlessly roll off out of band signals before they can cause the amplifier to slew limit and perhaps cause audible in band artifacts.

JR

Title: Re: Sound Is Subjective
Post by: John Roberts {JR} on February 18, 2008, 08:59:34 pm
SteveKirby wrote on Mon, 18 February 2008 19:40


Are you thinking of Spectral?  I think they were based in SF and founded on the premise that bandlimiting to 20kHz created slew limiting bluring time base information that provided directional cues.
There was an arm of the company that made records,  Reference Recordings.  I have one record of theirs with Stephen Gordon playing Chopin.  Lots of ambience that sounds like the rear third of the hall.


Sorry for the senior moment.. No not Spectral either.. I think it may have been a Canadian company with a distinctive but somewhat oddball name. I can just about form a mental picture of the guy (short, dark hair). I think he made a splash at one NYC AES show. But like I said it was a big deal one year and gone in like 2 years or less.

JR
Title: Re: Sound Is Subjective
Post by: Andy Peters on February 18, 2008, 11:06:42 pm
Ted Olausson wrote on Mon, 18 February 2008 18:20

Andy Peters wrote on Tue, 19 February 2008 02:14


OK, smart guy, why not try it -- remove the filter and see how long the amp lasts before ultrasonic oscillation destroys the output stage.


What does inputcap have to do with oscilliation!? it is a inputbuffer after the cap...
-If so, it would oscilliate when there wasnt any connector in the amp....


Ummm, whooops. I have to apologize!

I missed the part about input filter.

-a
Title: Re: Subwoofer amps - what are we REALLY hearing?
Post by: Mike {AB} Butler on February 19, 2008, 08:43:30 am
Tim McCulloch wrote on Mon, 18 February 2008 18:47

Mac Kerr wrote on Mon, 18 February 2008 17:43

Tim McCulloch wrote on Mon, 18 February 2008 18:42

Can we stick a fork in this thread?  It's done....

Tim Mc
It was done on day one.

Mac


Hmmmm... Let's carve it up and serve it...  lots of tofu; most of the real meat went unnoticed.

Tim Mc

... Making it a Tofurkey!!  Cool
Yes, we should lock this one, now.. It wasn't really worth it in the first place..