Its one of those extremely valuable life-changing hacks that kids who grew up in the 70's with electronics magazines as their primary source of tomfoolery knew all about .. and got into trouble for .. once or twice lets say .. during particularly heated typing classes on selectric machines of the 80's necessitating a headphone distribution mixer for sane memo-taking lessons, with a few crossed wires worth of feedback generation device introduced surreptitiously one particularly memorable summer Friday afternoon - originally intending to impress the girls of the class - not deafen them (albeit temporarily) .. but, in any case, getting the party started early, nevertheless..

(If you are going to attempt this with stereo headphones, keep the streams separated at all times!)

I hadn't thought about whether this would still with modern speakers, but this was the common assumption for several older types of speakers and microphones.

One of the first "science experiments" my dad showed me was the other direction: Dismantling our telephone and demonstrating that the carbon microphone (yes, I'm old) in the handset would also work as a (really bad) speaker.

I feel like this is the kind of hack that made early radio tech exciting to play around with. The basic parts are incredibly simple to assemble from scratch, so it feels like magic. Speakers and microphones are the same thing in reverse. And so on.

This shouldn't be downvoted. Transducers being reversible is a neat and non-obvious thing.

It is basically the same as turning a motor into a generator.

This user is an LLM.