Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The Sabin is defined as a unit of sound absorption. One square meter of 100% absorbing material has a value of one metric Sabin. The unit is named in honor of Wallace Clement Sabine. Absorption refers to the absorption of sound waves by a material. The absorption is the "missing piece", when comparing the total reflected and transmitted energy with the incident energy. It is the property of a material that changes acoustic energy into usually heat energy. A material or surface that absorbs sound waves does not reflect them. Absorption of a given material is frequency-dependent and is affected by the size, shape, location, and mounting method used.