@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.
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?
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Some people can sit on a small rise above a serene valley on a beautiful spring day and just marvel at the wondrous view. Others never get to really enjoy the view because they get too wrapped up in trying to figure out why it's so wondrous. As Bonnie Raitt sang, "Life gets mighty precious when there's less of it to waste." In my golden years, I much prefer to sit back and enjoy the view, or in this case, the sound of my system, for what it is. I'm happy to let all the young inquisitive minds take my place wondering why it is. |
@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. |
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