Introduction :
Sound waves travel in air as progressive longitudinal waves. Elasticity and inertia of the air enable the sound wave to propagate with certain velocity. Sound cannot be transmitted through vacuum. It can travel through any solid, liquid and gas. All the frequencies of the vibrating bodies can not produce the sensation of hearing.
Sound is a type of energy propagated in longitudinal waves. The source of sound could be any body which is vibrating. Some of the examples are a tuning fork which is excited, the wire of a stringed instrument being plucked , a bell which is struck with a hard thing, etc. When a sound wave is incident on any surface, a part of the incident energy is always absorbed. Absorbption of sound energy vary with different substances.
Thick screens or curtains, mats, carpets, wood, card boards are some of the examples of sound absorbers. Human bodies are very good absorbers of sound. Best absorbers are those which absorb sound completely. Open windows and doors are therefore perfect absorbers. The characteristic absorption of a surface can be different at different frequencies.
Absorption coefficient of sound wave:
Absorption coefficient : The absorption coefficient of a surface is defined as the ratio of the sound energy absorbed by the surface to the sound energy absorbed by an open window of equal area in the same time.
If Es and Ew are the amounts of sound energies absorbed by a given surface and an open window of the same area during same time, then
The absorption coefficient a = `(Es)/(Ew)`
Thus if 'a' is the absorption coefficient of a surface and s is the surface area, the sound energy absorbed by it is given by A = as. Absorption coefficient 'a' has no unit but the SI unit of 'as' is metric sabin.
The absorption coefficients of certainsubstnces at a frequency of 512 Hz are given below.
Sound waves travel in air as progressive longitudinal waves. Elasticity and inertia of the air enable the sound wave to propagate with certain velocity. Sound cannot be transmitted through vacuum. It can travel through any solid, liquid and gas. All the frequencies of the vibrating bodies can not produce the sensation of hearing.
Sound is a type of energy propagated in longitudinal waves. The source of sound could be any body which is vibrating. Some of the examples are a tuning fork which is excited, the wire of a stringed instrument being plucked , a bell which is struck with a hard thing, etc. When a sound wave is incident on any surface, a part of the incident energy is always absorbed. Absorbption of sound energy vary with different substances.
Thick screens or curtains, mats, carpets, wood, card boards are some of the examples of sound absorbers. Human bodies are very good absorbers of sound. Best absorbers are those which absorb sound completely. Open windows and doors are therefore perfect absorbers. The characteristic absorption of a surface can be different at different frequencies.
Absorption coefficient of sound wave:
Absorption coefficient : The absorption coefficient of a surface is defined as the ratio of the sound energy absorbed by the surface to the sound energy absorbed by an open window of equal area in the same time.
If Es and Ew are the amounts of sound energies absorbed by a given surface and an open window of the same area during same time, then
The absorption coefficient a = `(Es)/(Ew)`
Thus if 'a' is the absorption coefficient of a surface and s is the surface area, the sound energy absorbed by it is given by A = as. Absorption coefficient 'a' has no unit but the SI unit of 'as' is metric sabin.
The absorption coefficients of certainsubstnces at a frequency of 512 Hz are given below.
S.No Substance Absorption Coefficient
1. Marble 0.01
2. Glass 0.028
3. Carpet 0.2
4. Heavy Curtains 0.52
5. Fibre glass 0.69
6. Open window 1.00
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