Acoustical Absorption Coefficient in a Diffuse Field of a Plane, Rectangular Material of Finite Dimensions Placed on an Infinite Perfectly Reflecting Surface

摘要

This study deals with the evaluation of the acoustic absorption coefficient of a rectangular surface of known impedance, placed on an otherwise perfectly reflecting area. The incident acoustic field is supposed diffuse. This problem corresponds to the measurement of the absorption coefficient in a reverberation room. An analytic expression (approximation) is given for the evaluation of the absorption coefficient. From this expression, valid for the case of a rectangular surface of finite dimensions, results are derived and given in the literature for the case of an absorbing strip (surface of finite width and infinite length). The numerical values obtained in the case of a rectangular surface of finite dimensions are greater than those obtained in the case of a surface of infinite dimensions. Values superior to unity can be observed. This corresponds to what is sometimes measured in a reverberant room.