Another thing that nobody seems to be bringing up: animals. I don&#x27;t know what&#x27;s the full range of hearing of rats, but they talk a lot over ultrasound, with little-over-22kHz band being used to signal danger, and something around 56kHz to signal friendliness&#x2F;food locations[0]. If their idea worked, they would likely piss off a lot of rats. Not many people keep rats as pets, but some other animals and usual city wildlife probably hear those ranges too.<p>[0] - source: my ex-gf had rats as pets and I did some googling a few years ago to figure out what kind of experiments I could do on them ^_^.