High-frequency deterrents work because music has little energy above 16 kHz

Evidence

These units have proved themselves to be successful deterrents, saving considerable police time and effort in moving on gatherings of young people, and they are now used quite widely in public spaces. The unit will work in the presence of other sounds such as music, which typically contains no high-level energy at these high frequencies. Young people report these high-level high-frequency sounds to be very annoying, unpleasant and irritating. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2575

Categorization

• XREF: Connects to the book’s spectra of everyday sounds — the 16 kHz band is nearly empty of competing energy.
• FICTION: A world where public space is acoustically zoned by age would make a good near-future setting.