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CamperBob2 3 days ago

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.

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.