Would it have been possible for the speakers of the time to emit those frequencies? Imagining the equivalent of a Twitch raid: "I'm done broadcasting so I'm going to send you to the next channel."
We had a TV that used ultrasonic sound to control the TV, When I was young I could fairly hear the tone from a couple of the buttons, though super faintly, but the dog would cock its head when certain buttons were used.
It would have been possible, but it would have been expensive and required electricity to work. The fact that they accomplished their goal with what amounts to a set of tiny spring-powered mechanical bells is a marvel.
I meant it more in the sense of one channel, when shutting down for the night, emitting the "next channel" tone such that every viewer's set would change to a channel that was still broadcasting.
Not really sure, doesn't seem like they'd bother to deaign speakers that make sounds we can't hear or broadcast them but that doesn't mean it wasn't possible