>Humans should be safe though since a common number for the high-end of human hearing is 20kHz. That doesn't mean it's safe for humans, it just means it's inau

>Humans should be safe though since a common number for the high-end of human hearing is 20kHz. That doesn't mean it's safe for humans, it just means it's inaudible to humans. In many circumstances, an imperceivable threat is far more dangerous than a perceivable one. Laser is one example. If a visible laser beam hits your eyes, your blink reflex will kick in and (hopefully) save you in time. But a laser beam outside the human visual spectrum will literally burn your retina out before you figure out what's going on.