Really? If I am interpreting what you wrote, you say that it is just a matter of buying a very good quality subwoofer and this makes low frequency distortion problems go away. That is just not right. A better motor, a larger enclosure, more drivers, a larger radiating area - all of these help. But low bass at realistic levels (and I don't mean car audio soundoff levels) will still have distortion that is orders of magnitude more than the amplifier.
If you don't believe me, look through the measurement data at the links listed here:
Index to Subwoofer Tests by Manufacturer/Model - Home Theater Forum and Systems - HomeTheaterShack.com
Tests were performed on a variety of DIY subs using very high quality drivers, and some very expensive commercial subs. Check out the distortion levels. These start at 1% and go up as SPL increases and frequency decreases.
It's well known that every driver's motor and suspension have nonlinearities that cause distortion at higher SPL, but these do not diminish to zero at low power. This means that there is a lower limit for any driver, and is most definitely NOT very low compared to amplifier distortion.
Yes, exactly. It's not easy to get true low distortion bass - that's why I said considerable expertise is required. For example, a carcase that vibrates, or transfers the energy imparted to the driver chassis to the room structure in significant amounts probably won't do it - throwing money, more of every thing, at the problem won't help unless there is a right attitude.
How does one hear all these intriguing things. I listened every possible way to ZZ top and the bass is distorted, in fact all the instruments are distorted badly. Does this mean I can fix all this up by getting a great sub-woofer? On my humble system the Bee Gees sound like the chipmunks would a sub-woofer correct this and make them sound like true baritones?
Poetic licence, 
... technically, the voltage rails are sagging, and being modulated by the current demands to the point of it being audibly obvious, the PSRR of the amplifying circuit is unable to cope. Subjectively, the treble integrity starts to collapse, the sound becomes congested, shouty. One can actually do experiments, "listening" to the voltage rails as they are stressed more and more by the level demanded - and there is almost a clear point where the cleanness of the rails starts to severely degenerate.
... technically, the voltage rails are sagging, and being modulated by the current demands to the point of it being audibly obvious, the PSRR of the amplifying circuit is unable to cope. Subjectively, the treble integrity starts to collapse, the sound becomes congested, shouty. One can actually do experiments, "listening" to the voltage rails as they are stressed more and more by the level demanded - and there is almost a clear point where the cleanness of the rails starts to severely degenerate.
At what volume is supposed to occur, given a reasonable amp? Anyway, none of this really concerns me, apart from "academic" interest (putting aside a fascination with the absurd), since I run active speakers.
I have 160VA transformers each side and I can't hear any "sag" because at that volume, no one can hear themselves think.
Abs
Yes, in one fell swoop you've bypassed a whole host of the usual electronics problems, by going active - which is not the situation for the usual audio setup.
Imagine taking just a single amplifier you're using there, say the one for the midrange, and turning your speakers back to fully passive, with crossovers exactly matching so the drivers handle the precisely same frequency ranges as now. And driving the now passive speakers with that single amp ...
Then, would you be happy to say "I can't hear any "sag" because at that volume, no one can hear themselves think." ... ?
Seems odd to me that you'd assume that distortion may be the cause of differences between amps. In my experiience of listening to various amps, differences have been perceived as noise modulation - not something that's in the current repertoire of measurements.
"noise modulation"?
I did a very quick search and didn't come up with much. Have you invented the term, and, if not, since you seem to know so much about it, why haven't you suggested a means of defining and measuring it?
If it isn't in the current "repertoire", is there any reason for this? You appear to be an engineer with significant knowledge (from the thrust of your posts), so it surprises me that you would post something as seeming disingenuous as this. Why is something so apparently obvious as "noise modulation" excluded from the myriad of methods used to subject audio devices to intensive scrutiny?
Abs
I did a very quick search and didn't come up with much. Have you invented the term, and, if not, since you seem to know so much about it, why haven't you suggested a means of defining and measuring it?
If it isn't in the current "repertoire", is there any reason for this? You appear to be an engineer with significant knowledge (from the thrust of your posts), so it surprises me that you would post something as seeming disingenuous as this. Why is something so apparently obvious as "noise modulation" excluded from the myriad of methods used to subject audio devices to intensive scrutiny?
Abs
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Oops they may have got this one wrong - a car is like a Class D amp (discrete explosions inside the cylinders) where the whole car (starting with the flywheel) takes out the bumps....
Back to topic - this patent for feedforward amplifier - I tried to find it and what I read didn't tell me anything interesting yet. Has anybody here the ability to provide a neat summary of what this invention offers - beyond prior art that is ?
Yeah you said that before. Its not any kind of explanation for the claim of disingenuity - rather its repeating the same claim.
@jcx - I'm aware of multitone but there's no standardized test (other than MTPR which isn't used in audio) with a music-like stimulus. The signal resulting from a crest-factor minimized 30 tone waveform isn't sufficiently music-like. But I might well be out of date - do enlighten me if so.
@jcx - I'm aware of multitone but there's no standardized test (other than MTPR which isn't used in audio) with a music-like stimulus. The signal resulting from a crest-factor minimized 30 tone waveform isn't sufficiently music-like. But I might well be out of date - do enlighten me if so.
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