when you put a speaker next to a microphone, why is the feedback always really high notes and not whatever pitch the microphone heard last?

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when you put a speaker next to a microphone, why is the feedback always really high notes and not whatever pitch the microphone heard last?

In: Physics

Suppose you have a sound with a certain frequency of its wave. The speaker, microphone, amplifier, etc. don’t operate instantly so when what the microphone hears comes out it is going to be combined with whatever the current ambient sound waves are. Even with a constant tone it is unlikely to be precisely synchronized or on some even multiple.

So now you have the two waves combined which tends to result in more peaks and valleys per sample period. Keep looping and it continues to increase the overall frequency of the wave.

The note is the resonant frequency of the system. That is, it is the frequency which is most strongly amplified in the amplifier/speaker/room/microphone/preamplifier combination.