[Mike-o-Matic]

That device was called an "Acoustic Coupler."



Arrgh!! MMmmmm... sweet, juicy '70s tech.

[backhoe]

That device was called an "Acoustic Coupler."

Yep, and modems ( modulator & demodulator were where I first encountered UARTs ( Universal Asynchronous Receiver-Transmitter ).

I can't remember exactly, but there was some damn chip- a 16640?- you could replace with a faster chip in hopes of goosing the transfer rate, back in the days of DTST software for DOS.