One of the many projects I’m involved with on the side of my main research project is the Health EFfects of Ultrasound in Air (HEFUA). It is investigating the question of whether the standards for high-frequency audible sound (~16 kHz – 20 kHz) and low-frequency ultrasound (~ 17.8 kHz – 30 kHz) are sufficient. This is especially important in light of the constantly increasing use of ultrasound in everyday life. I know I was continually annoyed around Austin, TX by a variety of sources that I could hear, but others couldn’t. Recently there was a really annoying high-frequency sound near the London Eye. Here is a spectrogram of it:
While most adults can’t hear these sounds, many children can. There is an Instagram hashtag #UltrasoundInAir where people report the annoying high audible frequency sounds they come across. If you are interested in learning more see this paper.