How can you eliminate negative feedback in an audio system?

Question

I know you lower the gain of the pick-up with respect to the speaker source, but often this is not practicable, how else can it be done?

I'm aware some manufactures offer feedback elimination, but how do they do this?

I tried to do this digitally by introducing a delay line and also tried to slightly modulating the input signal i.e. increasing the frequency (in the hope that this would break the loop of resonant frequencies), but this didn't work. Any ideas, am just interested.

Answer 1

Use noise canceling microphones, or best bet get away from the speakers. Get the physical space between microphones and the speakers as great as you can. If you are in a small area, get the microphones out in front, and the speakers behind you. If the microphones can "hear" the speakers, then your system is going to howl. Physical separation, by distance, is a must, as well as having the speakers behind you, but off to the sides of your performing area You can also put the speakers out in front as well. The basic thing is separation between the microphones and the speakers. That is how you break the positive feedback loop.

Answer 2

Why would you want to do that?

Without negative feedback, you would have huge distortion, poor frequency response, and other problems.

The gain will increase, a lot,  if you remove negative feedback.

If you really want to do that, just remove all the components in the feedback loop.

Answer 3

Your problem is positive, not negative feedback. Negative feedback is something implemented in the amplifier at the circuit level -- it promotes stability, wider frequency response and lower distortion.

The annoying squealing you're talking about is the result of positive feedback from speakers to microphone. It can be ameliorated by actively phase-shifting those frequencies that are causing the feedback, but this requires sensing and software intervention -- not something you easily add to a system via a 3rd-party device.

In my experience, the only way to beat feedback in a real-world situation is to use highly directional microphones on the stage (not cardioid or omni).

Answer 4

Isolate the input from the output. Use a highly directional microphone. Use shielded wiring on anything in front of the first stage (pre amp) of your audio amplifier.

I think positive feed back is your problem rather than negative feed back. Your system is apparently going into oscillation. Random noise or 60 cycle hum in the pre amp is enough to start the oscillation.

These are old timey tips and may be obsolete