Not sure if it's mentioned in the article but microphones can be speakers too...

Only dynamic mics, which are relatively rare and seldom encountered without an attached preamp. The vast majority of mics for PCs are condensers and electrets.

Anything can be a speaker, briefly and only once, if you apply enough voltage to it...

I recall when I was a kid decades ago, being able to plug a speaker directly into the microphone jack and use it as a microphone, without any modifications whatsoever.

We could do the reverse too, plug a microphone into the speaker jack and hear sounds coming out from it.

same with solar panels, they can be reversed to emit light.

> perfectly sound.

I hear what you did there