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[Andy Peters]

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

[Bob Leonard]

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.

[Dave Rickard]

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.

[Dave Rickard]

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)

[John Roberts {JR}]

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

[Pascal Pincosy]

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 . 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 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.

[Andy Peters]

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

[Tim McCulloch]

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

[Bob Lee (QSC)]

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.

[Richard Rajchel]

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.