It's not exactly that straightforward. In general any modern audio equipment will run up to 20kHz since that's generally accepted as the range of human hearing. From what I can tell, the lowpass filters built in to equipment (eg antialiasing on ADC/DAC) attenuates starting at 19 or 20 kHz. But these are realized as low order physical filters, meaning they roll off slowly, so you'd have to start attenuating at something much lower to truly remove the 18-20 range. That would introduce distortion where the rolloff starts, which you probably don't want.

Things like Apple TV/Chromecast are serving ads and are hooked up to audio systems that are usually quite capable. And this could easily just shift to being done within the range of computer speaker production/human hearing and it would sound like a glitch at best (if audible at all).

From some quick digging I did in a Github repo attempting to reverse-engineer the 'audio beacons', the frequencies used by at least one startup using the technique are in the 18kHz range[1].

https://github.com/MAVProxyUser/SilverPushUnmasked/commit/bc...