The range of human hearing is generally considered to
be 20–20 000 Hz for young individuals, the upper limit de
clining with increasing age. Frequencies above 20 kHz ~ul
trasound! are generally considered to be inaudible by con
vention ~see Kryter, 1985, p. 456!, even though frequencies
up to 30 kHz have been ‘‘heard’’ through bone conduction
~as cited by Yeowart, 1976!. The focus of the present review
is on the lower end of the frequency spectrum. In selecting
the frequency range, we decided to treat low-frequency noise
as including what is normally taken to be infrasound ~see
Fig. 1!.