Sound Absorption
Caused by the inverse square law, a small part of a sound wave is lost to the air or other medium through various physical processes. One necessary process is the direct conduction of the vibration into the medium as heat, caused by the conversion of the coherent molecular motion of the sound wave into incoherent molecular motion in the air or other absorptive material. Another cause is the viscosity of a fluid medium (gas or liquid). These two physical causes combine to produce the classical attenuation of a sound wave. This attenuation type is proportional to the square of the sound wave’s frequency, as expressed in the formula α/f2, where α is the attenuation coefficient of the medium and f is the wave frequency [Online Encyclopedia Britannica].
Refers to the process by which a material, structure, or object takes in sound energy when sound waves are encountered instead of reflecting the energy. Part of the absorbed energy is transformed into heat and transmitted through the absorbing body. The energy transformed into heat is said to have been 'lost' [D’Antonio, Cox, p.18].
It measures the amount of energy removed from the sound wave as it passes through a given thickness of the material. While propagating from air into an absorbing material, the sound wave could experience reflection or absorption, thereby losing energy and experiencing dampening effects. In a polymeric material, sound absorption takes place by transforming sound waves into heat. Sound absorption is necessary for soundproofing [Sciencedirect.com].
Sound absorption.Encyclopedia Britannica. Retrieved from: https://www.britannica.com/science/sound-physics/Sound-absorption#ref527191
Trevor, J. Cox, D'Antoni, P. (2009). Acoustic Absorbers and Diffusers: Theory, Design and Application. London: Spon Press. Sound absorption. Sciencedirect.com. Retrieved from: https://www.sciencedirect.com/topics/engineering/sound-absorption.
Acoustic Absorbers and Diffusers: Theory, Design and Applicatio.CRC Press .2009.Peter D'Antoni