Not exactly related, but what I found interesting was a recent invention which relies on the superposition of ultrasound waves (which, you may know, can be tightly focused) to produce audible sound at a target. The result is a 'whisper beam', where you can point it at a target in a crowd and only that target can hear your sound. I can already see marketing execs drooling over this...
I don't think something like that would require
lots of marketing, it'll be snatched off the shelves...
It would probably be spread by word of mouth.
Ultrasound can be deadly at certain frequencies with high enough volume.
An acoustic cannon may be used to shake, empty, then destroy a building.
Ultra-low acoustic frequencies might make one crap their pants. What a way to stop an army in its tracks? (Watch those subwoofers!)
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