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What happens to back EMF with a feedback amplifier?

I was having a discussion with an engineer colleague of mine and we were discussing negative feedback. He said that it should work just fine but only if the load was ideal (ie. a perfect resistor). He thought that because a speaker is always somewhat reactive that some (or a lot depending on the speaker) of the energy put into the speaker finds its way back to the output of the amplifier.

I asked him then where does that energy go, is it dissipated as heat or is it sent back through the feedback loop. He replied that both things occur and he felt that one of the biggest negative side effects of negative feedback was this back EMF being sent back to the input of the amp and reamplified, now way out of phase with the rest of the feedback signal. One might also argue that enough time has passed that this signal now being put back into amplifier bears no resemblance at all to the signal that is being amplified at that instance.

It seems to me that what you have then is a situation where the error correction is in fact introducing more error and this gets perpetuated indefinitely. My engineer friend felt that this is one of the major reasons that amps with high negative feedback often sound constricted with squashed macro dynamics and poor low level resolution as the signal is being smeared by this now error inducing feedback.

Based on a logical flow of the signal and the fact that music is mostly not steady state these arguments make sense and seem to fit well with my listening "observations".

Please comment.

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Topic - What happens to back EMF with a feedback amplifier? - morricab 05:01:34 08/17/06 (121)
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