Microphonics, Feedback and Bob Carver

That is, the resistance to my fingers or external sources is causing the amplifier to respond with enough current to keep the voltage at zero, so it's not a zero sum game, I think.

@erik_squires You exert far more energy with your fingers on the cone than sounds in the room will! To me this seems a non-issue. Again, if the amp is on, the speaker is harder to move due to the output impedance and feedback having nothing to do with it. To show this for yourself, put a 0.5 Ohm resistor across the speaker terminals and you'll see what I mean. The resistor has no feedback yet the speaker is much harder to move.

When I'm at audio shows and there are multiple speakers in the room, I short out the terminals of the unused speakers so they won't resonate.

@erik_squires, i wonder why bob carver

put 15W edcor output transformers in an amp he claims does 80WPC. 

I recall a series of articles in AudioXpress on a topic similar to what the original poster raised referred to as “Back EMF.”  Here’s a link to the articles.

After analysis with a lot of math the author determines that Back EMF is not an issue worth worrying much about.  Interesting thought experiment though.  Any unwanted cone movement generates a signal that an amplifier using feedback tries to compensate for.

Thanks so much, @pdspiegel !!