Sound absorption is the process by which sound energy is taken up and converted into heat by porous, soft or fibrous materials, so that the sound is not fully reflected back into a room.
How sound absorption works
When sound waves strike a surface, part is reflected and part is absorbed. In absorbing materials, the sound waves penetrate the pores or fibres, where friction converts them into a small amount of heat. The more energy that is absorbed, the less sound is reflected.
The degree of absorption is expressed by the absorption coefficient (alpha, α):
- α = 0 means full reflection (hard surface)
- α = 1 means full absorption (open window)
- Most materials fall somewhere in between
High frequencies are absorbed most easily; low tones require thicker or specialised absorbers.
Application
Sound absorption is used to improve the acoustics within a room and reduce reverberation. Examples include:
- Acoustic ceiling panels in offices and classrooms
- Wall panels of mineral wool or foam in studios
- Soft materials such as carpet, curtains and upholstery
- Baffle panels in sports halls and restaurants
Note: absorption lowers reverberation within a room, but does not stop sound from reaching another room. For that you need sound insulation.
Related terms
- Acoustics
- Reverberation
- Absorption coefficient
- Sound insulation
- Mineral wool
- Decibel
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