Rarefaction

Rarefaction is the reduction of an item's density, the opposite of compression.

This expansion behaviour contrasts with that of pressure increases, which gets narrower with time until they steepen into shock waves.

A natural example of rarefaction occurs in the layers of Earth's atmosphere.

Rarefaction can be easily observed by compressing a spring and releasing it.

By forcing the reduction of density (loss of oils and other impurities) in the cellular structure of the soundboard, a rarefied guitar top produces a tonal decompression affecting the sound of the instrument, mimicking aged wood.

An example of rarefaction is also as a phase in a sound wave or phonon . Half of a sound wave is made up of the compression of the medium , and the other half is the decompression or *rarefaction* of the medium.