Cats and Household Appliances
If you have cats, you have probably noticed they hate the vacuum cleaner and other loud home appliances. This may well be due to the ultrasonic sound produced by these devices, sounds we cannot hear but that fall within the cat's extended high-frequency hearing ability. Our cats flee in haste when the Miele S 172i emerges from its hiding place. It turns out that particular vacuum produces plenty of ultrasonic sound. Other appliances that I hate myself, like the hair dryer, seem not quite so motivating for the cats. As we see below, the hair dryer produces relatively less ultrasonic sound. (Note that the sound levels are not comparable, only the spectra.)
It seems not all cats are repelled by a vacuum cleaner, however. Our late cat Dexter loved being vacuumed with our old Eureka 1684 B canister vacuum. Unfortunately I have not measured its spectrum, but it may well not have generated a significant level of ultrasonic sound. While he might have been hearing-impaired from years of hanging around the rock music, he could hear the can opener from 1000'.
I first recorded a vacuum cleaner - the one I used on Dexter - for Numbskulls. Later, Dan Levitin and I recorded about a dozen different vacuums as part of a research project involving William's Syndrome children who exhibit extraordinary sound timbre accuity. The Menlo Vacuum shop was very accomodating if bemused. I later bought our Miele from them.