SOUND-ABSORPTION OF A CAVITY-BACKED MEMBRANE - A STEP TOWARDS DESIGN METHOD FOR MEMBRANE-TYPE ABSORBERS

This paper deals with a theoretical study of the sound absorption char acteristics of a membrane-type sound absorber. A closed-form analytica l solution for the sound absorption coefficient of an infinite membran e with an air-back cavity is produced by making a minor modification t o the solution for a cavity-backed infinite elastic plate which was de rived in the previous paper. To analyse the mechanism of absorption, t he solution is rearranged in a form which points out the contribution of each element of a membrane-type sound absorber. The contribution of the cavity is found to be dominant, and that of the absorptivity of t he source side surface of the membrane is rather small. In the case of an elastic plate, the contribution of the loss factor is found neglig ible. The effects of the parameters of the sound absorption system are discussed in the light of calculated results. Furthermore, the method to predict the peak-frequency and the peak value of the oblique-incid ent absorption coefficient of the membrane-type sound absorber is pres ented. The method satisfactorily explains the relationship between the absorption characteristics and the parameters. It is also applicable to panel absorbers. It can be useful for the design of the purpose-mad e membrane-type or panel absorbers, and for the sound field prediction within boundaries made from this type of absorber. Copyright (C) 1996 Elsevier Science Ltd.