I’ve been trying to get a solid answer on that, but no luck so far. From what I’ve read, it seems that ultrasonic sound can at worst cause nausea and/or a headache; however, the damaging factor of a sound wave is its intensity. The pitch has more to do with annoyance levels than actual harm. So that would mean a high-dB noise could be damaging regardless of audibility, right? But I’ve also found a bunch of articles and safety papers that say there’s no serious health risks in prolonged exposure to loud, ultrasonic noise (takes deep breath) – though they also point out that no in-depth testing has been done.
So, my question is this: would an ultrasonic sound in excess of, say, 120 dB cause serious problems with subjects that couldn’t hear it?
I’ve done a lot of work with computed sonography machines, the kind that give you pictures of a baby in the womb or a beating heart.
These have been proven quite safe and have been thoroughly tested for twenty years.
However if you are talking about something like traffic or subway train vibrations that are just below the hearing threshold, yes they are a problem, and will affect the hearing in the low ranges. This is particulary a problem in factory settings, and OSHA has rules about monitoring for it.