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Author Topic: Subwoofer amps - what are we REALLY hearing?  (Read 31988 times)

Richard Rajchel

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Re: Sound Is Subjective
« Reply #20 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.
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Bob Leonard

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Re: Sound Is Subjective
« Reply #21 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.
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John Roberts {JR}

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Re: Sound Is Subjective
« Reply #22 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
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Andy Peters

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Re: Sound Is Subjective
« Reply #23 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
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John Roberts {JR}

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Re: Sound Is Subjective
« Reply #24 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

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Chuck Fry

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Re: Sound Is Subjective
« Reply #25 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
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Tim Duffin

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Re: Subwoofer amps - what are we REALLY hearing?
« Reply #26 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

Scott Smith

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Re: Sound Is Subjective
« Reply #27 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?
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John Roberts {JR}

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Re: Sound Is Subjective
« Reply #28 on: February 05, 2008, 07:22:32 pm »

perhaps

JR
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Tim Duffin

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Re: Sound Is Subjective
« Reply #29 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


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