Prediction of the reverberation absorption coefficient of finite-size membrane absorbers

This paper presents a method to predict the reverberation absorption coefficient of a finite-size membrane absorbers composed of a single- or double-leaf membrane structure of various configurations. In order to predict the sound absorptivity of such an absorber, it is needed to consider that sound is incident from both sides of the absorber, which has not been accounted for the previous studies on membrane absorbers. The edge effect also needs to be considered if the absorber is rather small. The present method is established based on the theory for absorbers hanged in a reverberation chamber developed by Fujiwara and Makita [J Acoust Soc Jpn (E) 1980;1:37-45]. The same theory requires the fraction of energy dissipation in the absorber, which can be obtained by the difference of absorption and transmission coefficients, and the difference is calculated by the theories for various membrane structures presented in the authors' previous work. An experimental study was also conducted to validate the present method: the predicted values showed good agreement with the measured ones. The numerical examples calculated by the present method are also presented to discuss the effect of the various control parameters, and it is suggested how to improve the sound absorption performance of double-leaf membrane absorbers with a permeable and an impermeable leaves.