Sound absorption coefficient (α)

Professional Definition

The sound absorption coefficient (α) is the ratio of the energy of the acoustic wave absorbed by a given surface to the energy of the acoustic wave incident on that surface.

In physical terms, it is a dimensionless quantity that takes values from 0 to 1. This value depends on the frequency of the sound and the angle of incidence of the wave. Mathematically, it can be expressed as α = E_absorbed / E_incident. In engineering practice, materials with a high α coefficient are crucial for reducing reverberation time in rooms.

Acoustics in Simple Words

Imagine throwing a tennis ball at various obstacles. If you throw it at a concrete wall, the ball will bounce back with almost the same force – this is the equivalent of a surface where α is close to 0 (total reflection). However, if you throw the ball at an open window, the ball will disappear outside and won’t come back – this is the ideal situation where α is 1.0 (total absorption).

Acoustic materials act like a dense sponge for that ball. Instead of bouncing back, the sound energy “gets stuck” in the porous structure of the material, converting into trace amounts of heat. The closer the material parameter is to a value of 1.0, the less noise returns to the room.

Summary

The sound absorption coefficient is a fundamental parameter in the design of acoustic adaptations. It allows us to precisely determine how many acoustic devices we need to control reverberation and ensure comfortable listening conditions.