Microphonics, Feedback and Bob Carver
First, I’m going to present a theory I don’t have a lot of investment in, I’m just curious about.
Bob Carver and I, at different times, have wondered about the ability of an amplifier’s feedback circuit to be impacted by a speaker’s natural microphonic attributes. That is, in a room and unplugged to an amp a speaker and microphone are broadly similar. A diaphragm is exposed to sound which moves a voice coil which generates an AC signal in proportion to the acoustic event. Of course, a speaker is a terrible microphone, but it can be one.
The question I’ve had, and then read Bob Carver also asked (but he’s not known for always being right, nor am I 😁) is whether part of the problem with negative feedback in an amplifier is that it can pick up in room sounds (such as from the other speaker) and react to it in a negative fashion.
While this is testable via equipment I don’t have, not to mention time/energy to do it right, I’m wondering if anyone has ever read any more on this subject they’d care to share?
Ah, but (apologies to Shakespeare) there's the rub. In order to keep the diaphragm from moving, current must flow. 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. |
@atmasphere To put this another way, the amp must produce an equal and opposite reaction to the incoming room noise (or fingers poking). That means that the current flowing through the output stage must be an analogue of that pressure. The voltage is zero, but not the current. :) |
While I appreciate your accolades, lets be honest. @atmasphere actually builds excellent and highly sought-after electronics for a living and if anyone should be called an expert it should be him. By comparison, I’m just a dabbler in a thousand little things. OTOH, ask me to compare how Dolby Surround functioned in motion picture auditoriums and how it differed from Dolby Digital and DTS and multi-track digital film and I probably have the edge. :) |
@erik_squires you said recently "welcome to AG where you get what you pay for and a whole lot less". I thought that was brilliant (comeback) but I'd say this is far from worth-less. And like the prior, I'm barely hanging on past, the speaker acts as a microphone! Carry on. |
