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.

  • $\begingroup$ What kind of system are you talking about? PA/Monitor to Microphone feedback? Something else? In any case, the frequency range is limited by the components involved and their frequency response. $\endgroup$ – Jazzmaniac Jul 15 '15 at 18:34
  • $\begingroup$ Yes, I would be interested in an answer for PA/Monitor to microphone feedback, but I'm also curious about for instance the situation where a user experiences feedback from a headset-microphone device, or any other situation where acoustic feedback is produced. It's true that I would be interested as to specifics detailing how, numerically speaking, the relevant components and their frequency responses influence the frequencies of the feedback. But what I'd most like to know is simply which frequencies I might find the feedback upon looking at a spectrogram. $\endgroup$ – itsumozenzen Jul 15 '15 at 19:55
  • $\begingroup$ A spectrogram of what? $\endgroup$ – Jazzmaniac Jul 15 '15 at 20:11
  • $\begingroup$ A spectrogram of the recording from the microphone (where the recording contains feedback). $\endgroup$ – itsumozenzen Jul 15 '15 at 20:35
  • $\begingroup$ The distance between the mic and speaker affects the feedback frequency. A large enough distance (tens of meters) might allow low frequency feedback if within the passband of the system with enough bass gain. $\endgroup$ – hotpaw2 Jul 16 '15 at 3:06

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