What causes audio feedback?

Question

I understand Audio feedback is caused by a "looped signal", that is, a signal which travels in a continuous loop. Most commonly a microphone feeds a signal into a sound system, which then amplifies and outputs the signal from a speaker, which is picked up again by the microphone. All of that I get.

But my question is, what causes the loud squealing noise? Shouldn't it just amplify the sound even more?

Thanks!

Answer 1

The amplifier has a limit to how much input it can handle. Once you've reahe that limit the amplifier goes into what's called saturation. This condition causes the amplifier to become an oscillator - it generates a sound at some frequency or frequencies determined by its capacitance, resistance and inductance. Saturation is not self sustaining since it has to be driven into this condition. Thus, once you remove the input signal, the amplifier recovers and is well behaved again.