What is the frequency range in which acoustic feedback can be found? Most importantly, is there some lowest frequency below which one can expect not to find any feedback?
My conclusion from the reading I've done and from working with a limited number of audio feedback samples is that it can be found anywhere from 900 Hz upward. However, I've also found an example where the feedback in question shows up in the spectrogram around 550 Hz. Now, the creator of that sound may well have shifted the sound's pitch down after recording it (I've asked the uploader and I'll wait for an answer). But in any case, it made me wonder if such a situation actually might arise in practice.