Phase Cancellation to Prevent Feedback Answered
The Grateful Dead's wall of sound prevented feed back by having two mics for each vocalist with one of the mics 180° out of phase of the other. Then mixing both mics on the same channel. So the only information that wasn't canceled was the voice.
This gave me an idea. I took a handset and added a mic facing backward from the existing mic. Then wired the second mic out of phase. Apparently there's more to it electrically then just wiring the other mic backwards because the handset went dead.
Is this possible with just parts salvaged from old phone equipment?