The audible range is 20 to 20,000 Hertz(20kHz). This is because the middle ear acts as low pass filter.Any sound wave having a frequency more than 20,000 is termed ultrasound. (Any frequency below 20Hz is infrasound). The velocity of sound in any given medium is constant. It is determined by the properties of the medium rather than the sound wave itself. The velocity is 0 in vacuum, increases with stiffness and against the density of the propogated medium. So it is slower in air than in water and in non-porous solid medium. It is 343 m/s in air and 1540 m/s in the tissues.
Transmission: Sound is transmitted as longitudinal waves in gaseous and liquid medium. In solids it is propogated as both longitudinal and transverse waves.
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