SPEAKE(a)R: Turn Speakers to Microphones for Fun and Profit [pdf] (2017)

me_jumper

This needs a (2017), I was so confused why this was published again, seemed so familiar.

jpc0

A magnet in a coil operates both ways, this is non intuitive but perfectly sound. Not sure if it's mentioned in the article but microphones can be speakers too...

dickfickling

I have vague memories of iPod Linux (or Rockbox, I can’t remember) having a feature where you could record voice notes using your regular headphones using the same technique

m4lvin

Okay, but how do I use this as a replacement when the mic is not working on Linux?

userbinator

Not all speakers work well as dynamic mics; and in fact turning on mic mode may enable the bias voltage, which could either burn out the voice coil or hold the diaphragm against the stop, making it even less likely to pick up any sound. Jack retasking, although documented in applicable technical specifications, is not well-known, as was mentioned by the Linux audio developer This could be a "bubble effect"; the Realtek codecs mentioned have a Windows utility to configure the jacks, which countless otherwise non-technical users would've seen and interacted with, so awareness of this feature is probably higher than they think. Fun fact: the "ALC" prefix in their codec names stands for Avance Logic, which was acquired by Realtek and they just kept that prefix well into the HD Audio era.

villgax

If this or an accelerometer based recording is what Meta uses to eavesdrop on in-person talk then color me pink

maqp

Some DJs use this principle when they need a hacky stage mic. They plug their headphones to the mixer's mic input, and shout to the speaker element.

AmmarSaleh50

don't let the CIA see this one

Se_ba

Tbh it's crazy that you can do it in some of the microwaves

rf15

As a kid I accidently plugged a mic into the speaker port and was surprised that, when I put my ear close to the mic, I could hear the computer sounds! It made sense in hindsight, and since then I knew they are kind of functionally equivalent.

VladVladikoff

When I was a teenager I was friends with an extremely poor kid who literally lived on the wrong side of the tracks. He couldn’t afford a microphone and used an old pair of busted headphones to rap into as a microphone. He had recorded and produced a whole album like this with Fruity Loops on an old computer he found discarded at the side of the road.

nailer

Vault 7 from wikileaks confirmed that yes, the CIA is using this.

Anechoic

This is how drive-thru kiosks work (principal, not the specific implementation). Source: I used to measure the “microphone” frequency response for a kiosk OEM.

riobard

why is jack retasking a thing…

analog31

A fun fact is that the ability of a single transducer to function as both a speaker and a microphone is the basis for establishing an absolute measurement of sound pressure. https://nvlpubs.nist.gov/nistpubs/jres/25/jresv25n5p489_A1b....

antirez

Similarly most leds are photo diodes, electric motors can be used to generate current, Peltier cells can be used to generate current, and so so forth. Many of such physical processes are invertible.

anonymousiam

While staying in a high-end D.C. area hotel, I once discovered a hidden hard-wired speaker under the bathroom sink. Somebody had written "F.B.I." on it with nail polish. I already knew that speakers could be used as microphones, and it occurred to me that putting a speaker in a hotel room in the name of "safety" would be a great cover story for a surveillance operation.

jnellis

When I did commercial fishing in Alaska, often the boats just had two speakers, one in the wheel house and one on the deck (long liner). You just talked into/toward the speaker.

jedbrooke

Fun fact, an electric guitar can also be used as a microphone if you shout in to it loud enough. We discovered this while fooling around with some guitars and such as teenagers. We had a 4 track input device that was separating vocals and instruments, but even after turning down the vocal track, we could still hear it in the instrument track. We then of course followed it up with some experiments deliberately shouting into the guitar and enjoying the distorted recordings that came out of it

olelele

A big speaker element is useful for micing kick drums.