Absorption Coefficients Clarification

By Pat Brown

Pat Brown helps the reader understand more about absorption coefficients.

A recent Syn-Aud-Con listserv thread brought out some interesting facts about absorption and absorption coefficients. A common definition of the unit of absorption, the Imperial Sabin, is that it is “one square foot of open window.” A metric Sabin is “one square meter of open window.” From this definition, it is tempting to associate unity with complete absorption. From this, a working definition of an absorption coefficient is that it represents the percentage of sound that is absorbed when a sound wave strikes a surface. So, a 0.5 coefficient means that 50% of the sound is absorbed. While elegant in it’s simplicity, the percentage definition doesn’t hold up under closer scrutiny.