| ▲ | nielsole 3 days ago |
| Asahi Linux (and likely MacOS too) uses the resistance of the speakers coils to detect overheating of same speakers and reduces volume. |
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| ▲ | squarefoot 3 days ago | parent | next [-] |
| That's the same principle used by cheap solder stations to regulate the tip temperature without employing a thermal sensor: they measure the heater resistance, presumably during the off state of the PWM signal that drives the heater. In that case the measurement is less accurate than using a real sensor, still good enough for cheap solder stations where a few degrees don't make a big difference. |
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| ▲ | floating-io 2 days ago | parent [-] | | Why would they do it during the off state? If they know the voltage and can measure the current that they're driving it with -- or vice versa -- they can use Ohm's law to calculate the resistance. They'd probably have to do that anyway. |
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| ▲ | derhuerst 3 days ago | parent | prev | next [-] |
| https://github.com/AsahiLinux/speakersafetyd |
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| ▲ | CamperBob2 3 days ago | parent [-] | | Interesting. If the voltage across the speaker voice coil can be sampled with enough sensitivity at a fast-enough rate, you have an undocumented microphone. | | |
| ▲ | xyzzy_plugh 3 days ago | parent [-] | | This is true of all speakers | | |
| ▲ | ssl-3 3 days ago | parent | next [-] | | It's true of all dynamic speakers -- the sort with a voice coil and a magnet. (But not all speakers are dynamic speakers.) | | |
| ▲ | planewave 2 days ago | parent [-] | | Would this also be true for electrostatic speakers as well? Though would probably would require greater gain/amplification or, potentially the application of some kind of bias voltage for the capacitive diaphragm of the speaker. Just speculation based on the shared operating principal with condenser microphones | | |
| ▲ | ssl-3 2 days ago | parent [-] | | With bias power, I think an electrostatic loudspeaker turns into a condenser microphone (a thing that provides varying capacitance in response to changes in pressure). I don't think that electrostatic loudspeakers all require bias power, so it's not quite as simple as using a dynamic loudspeaker backwards is. It is a neat idea, though. A big, flat-panel microphone would be interesting to play with. |
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| ▲ | BobbyTables2 3 days ago | parent | prev | next [-] | | But not true of all codecs… Do you think Apple put a hidden microphone in their devices by pure accident? | |
| ▲ | TacticalCoder 2 days ago | parent | prev | next [-] | | Others who know that better than me and commented but... First time I read that, as a kid, here was I plugging my headphones into the input jack of my parents' soundsystem and, sure enough, it worked as mic (although at as super ultra low volume but I clearly remember it worked). | |
| ▲ | CamperBob2 3 days ago | parent | prev [-] | | Exactly. |
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| ▲ | nick3443 3 days ago | parent | prev [-] |
| Also used in electric motor controllers to monitor winding temperature. |
