[riffic]

EDIT i'm wrong the speaker was inside the armrest.

I wouldn't be surprised if the channel selector wheel was a simple mechanical acoustic coupler rotating to connect or cap upstream source tubes. I remember it as well flying in the late 80s or early 90s.

[denton-scratch]

> a simple mechanical acoustic coupler

I get what you're saying, and I think that's plausible. But as far as I'm concerned, an acoustic coupler is/was a type of modem, into which you plugged an ordinary telephone handset. You had to have a telephone that had hemispherical mike and earphone; it didn't work with e.g. a trimphone. Expected performance: 9,600 bits-per-second.

[riffic]

"coupling" then, whatevs.

lemme see if I can dig up a patent number for the channel switcher wheel and put this pondering to rest.

seems the inventing corporation is still around haha

https://avidproducts.com/2023/12/08/celebrating-70-years-of-...