Timeline for What does the frequency of oscillating microphone feedback depend on?
Current License: CC BY-SA 4.0
10 events
| when toggle format | what | by | license | comment | |
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| Aug 10, 2023 at 17:26 | vote | accept | Theodote | ||
| Aug 9, 2023 at 8:46 | comment | added | Marcus Müller | Re 2) yep! And that's also why the technician at a venue adjusts the filter curve of the processing happening between mic sand speaker when they combat the occurrence of feedback. | |
| Aug 9, 2023 at 4:56 | comment | added | Theodote | @ Hilmar @Marcus Müller thank you for the detailed feedback! I understand the implications of the 180° phase shift and how it results in system instability, causing the resonant feedback. Does that mean that 1) you can get different resonant peaks at different distances/wavelengths 2) the resonant peaks depend on the electromechanical characteristics of both devices, which, in fact, shape their frequency responses? | |
| Aug 8, 2023 at 21:54 | comment | added | Hilmar | @Theodote: rooms where acoustic reflections are negligible are very rare owing to the fact that they are extremely expensive (don't ask how I know :-) ). Even in a very dry room, you still have the directivity of the microphone and the speaker. In fact, one of the main remedies is to use a cardioid microphone and orient it so that the null points towards the speakers. Distance does indeed play a role and in general further is better but the exact relationship is quite complicated and depends on the type of speaker (cylindrical is better than spherical) | |
| Aug 8, 2023 at 20:55 | comment | added | Marcus Müller | You get that in your anechoic chamber when the distance between microphone and speaker (including the phase shift that all the electronics introduce) amounts to half a wavelength. Wavelength is inversely proportional to frequency, so you get exactly one frequency that has a phase shift of 180°. So, yes, Hilmar's model fits your scenario perfectly. | |
| Aug 8, 2023 at 20:52 | comment | added | Marcus Müller | @Theodote the room response does play a significant role! Hilmar's math explains every linear feedback system you can model, so even the scenario you describe in your comment. Even if your channel was perfectly "flat" in spectrum (which it isn't, every speaker and every microphone are frequency-selective), then you'd still incur a phase delay, which fully defines the feedback phenomena you're getting. Remember how the closed-loop transfer function becomes -1 for division by zero, i.e. feedback? exactly! -1, and inversion, is mathematically a pure phase shift by 180°. | |
| Aug 8, 2023 at 20:42 | comment | added | Theodote | Thank you for your detailed response @Hilmar! The thing is that this effect is also present soundproof rooms and on volumes where acoustic reflections are negligible. In this case, I feel like the room's characteristic transfer function doesn't play a significant role in the phenomenon. I would like to know more about how it is related to the distance between the mic and the loudspeaker, if it is at all. | |
| Aug 8, 2023 at 20:37 | vote | accept | Theodote | ||
| Aug 8, 2023 at 20:38 | |||||
| Aug 8, 2023 at 20:35 | vote | accept | Theodote | ||
| Aug 8, 2023 at 20:37 | |||||
| Aug 8, 2023 at 14:30 | history | answered | Hilmar | CC BY-SA 4.0 |