Absorption (acoustics)
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Acoustic absorption is that property of any material that changes the acoustic energy of sound waves into another form, often heat, which it to some extent retains, as opposed to that sound energy that material reflects or conducts. Acoustic absorption is represented by the symbol A in calculations. Absorption is not a single mechanism of sound attenuation: propagation through a heterogeneous system is affected by scattering as well.
The absorptive of a given material is frequency-dependent and is affected by size, shape, location and the mounting method used. Porous insulative materials such as mineral wool or glass wool are effective sound absorbers compared with good conductors such as metals. Micro perforated plates, however, supply "hard" absorptive surfaces.
Acoustic absorption is important in the analysis of sonar. The primary substance in seawater that is responsible for absorption is magnesium sulfate. The secondary substance is boric acid. The most common sea salt, sodium chloride has virtually no effect on sound absorption.
