How are sound waves classified?

Explanation

Sound waves can be classified in three groups according to their range of frequencies.
(1) Infrasonic waves: Sound waves having frequencies below 20 Hz are called infrasonic waves. These waves are produced during earthquake. Human beings cannot hear these frequencies. Snakes can hear these frequencies.
(2) Audible waves: Sound waves having frequencies between 20 Hz to 20,000 Hz (20 kHz) are called audible waves. Human beings can hear these frequencies.
(3) Ultrasonic waves: Sound waves having frequencies greater than 20 Hz are known as ultrasonic waves. Human beings cannot hear these frequencies. Bats can produce and hear these frequencies.