Subsonic is an ambiguous word.
- A speed lower than the speed of sound is called subsonic.
- Sound that is too low-pitched to be consciously perceived by humans are called infrasound or subsonic. Subsonic sound 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. Infrasonic sound waves in nature are produced only by earthquakes.
