[nihzm]

I have a friend who built one of these as their thesis. IIRC they were telling me that the air through which the sound beam propagates acts as a low pass filter, so if you're at the correct distance from the device the high frequency energy should have dissipated.

Interesting stuff, I wish I had more time to learn about what they where doing.

[binary132]

I was thinking about how the air itself must be contributing to the construction of the (standing?) sound wave as a resonator.

[nihzm]

Not sure if there are standing waves involved, or resonance. I presume it is very similar to a phased array [1] for beamforming in antennas, except that then anisotropic properties of medium may not be negligible to construct the wavefront (temperature gradients & wind), which is probably also why these devices do not sound great. To produce a high quality waveform at the receiving end the physics probably becomes quite involved rather quickly.

[1]: https://www.analog.com/en/resources/analog-dialogue/articles...