Basics of Sound Waves


We all are familiar with the experience of sound. Most of the people, who works daily in the sound field, does not think about the science of sound. It is good to know about the medium in which we are working.

Sound can be generated by any vibrating source. It can be either a musical instrument, loudspeaker diaphragms or voice from a person.

Longitudinal Waves

Sound waves are longitudinal in nature. It works on compression and rarefaction phenomenon. The direction of wave motion is parallel to the direction of particles.

Compression is the region of high pressure and Rarefaction is the region of low pressure.

In this example, when the diaphragm of a loudspeaker vibrates, it moves forwards and backwards and pushes the air molecules. On forward push, the air molecules get squeezed resulting in the area of high pressure called as compression. On pulling back the diaphragm, the air molecules get separated resulting in the area of low pressure called as rarefaction. That compression and rarefaction travel away from the sound source in the form of wave motion.

Do air molecules really travel from one place to other ?

No, The air molecules only vibrates forward and backward. They never go anywhere from one place to other. If they go, then it’s called as wind.

Point Source

Molecules are very small and they are considered as point sources. They emits sound equally in all directions, hence called as omnidirectional. Generally sound waves travel in a straight-line path, but in case of low frequencies, it will spread in an arc shape.

A sound source is called as point source if the size of the sound source is less than emitted wavelength. A point source follow’s the inverse square law.

Inverse Square Law

Sound pressure halves for every doubling of distance from the source.

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