People commonly say that the audible frequency range of human beings is roughly 20Hz to 20,000Hz, but I guess old-timers of this forum know very well that the second figure is a slightly optimistic estimate, with the upper range often receding noticably as age progresses.
People who can hear the higher frequencies are joked as having bat's ears, but the other day, I heard someone mention that the audible frequency range of bats usually starts with the lower boundary of 20,000Hz.
This made me smile, because that would mean that a bat would be quite deaf as far as human speech perception is concerned, the same way that people are quite deaf and dum as far as bat echo-location is concerned. People with bat's ears would be deaf and dumb to people with human ears, and vice versa.
How batty!
(Pun intended.)PS. I tried searching for the audible frequency range of bats, and it seems that some species of bats can hear sounds as low as 12,000Hz. On the other hand, it looks like bat detectors tend to start catching frequencies from 20,000Hz and up.