something like this. https://en.wikipedia.org/wiki/Underwater_telephone https://en.wikipedia.org/wiki/Underwater_telephone very hard to find info on how it wo

something like this. https://en.wikipedia.org/wiki/Underwater_telephone https://en.wikipedia.org/wiki/Underwater_telephone very hard to find info on how it works or at what ranges. but this suggests that it shifts sounds down to lower pitches to travel further. https://en.wikipedia.org/wiki/Modulated_ultrasound https://en.wikipedia.org/wiki/Modulated_ultrasound