Subsonic

A speed lower than the speed of sound is called subsonic or infrasonic.

The concept of subsonic speed is not very interesting in everyday life since almost all speeds are subsonic. Therefore, the term is mostly used in technical jargon, especially when talking about transitions to or from supersonic speeds.

Subsonic sound, however, has an effect on human hearing. The frequency range of normal human hearing is 10-24,000 hertz. Researchers have found that frequences as low as one hertz (one cycle per second) have a definite effect on the inner ear, affecting its equilibrium and causing dizziness[?].

Subsonic sound waves in nature are produced only by earthquakes.

See also: supersonic