Audible, Ultrasonic And Infrasonic Waves
(a) Audible Wave :
The human ear is sensitive to sound waves of frequency between 20 Hz to 20 kHz.This range is known as audible range and these waves are known as audible waves.
Example.Waves produced by vibrating sitar, guitar, organ pipes, flutes, shehnai etc.
(b) Ultrasonic waves :
A longitudinal wave whose frequency is above the upper limit of audible range i.e. 20 kHz, is called ultrasonic wave. It is generated by very small sources.
(c) Infrasonic wave :
A longitudinal elastic wave whose frequency is below the audible range i.e. 20 Hz, is called an infrasonic wave. It is generally generated by a large source.