Sound absorption of porous materials – Accuracy of prediction methods

The normal incidence sound absorption coefficient of porous materials can be predicted when the specific acoustic impedance of the material is known. Impedance prediction methods have been published by Delany and Bazley, Qunli, Miki, Mechel, Mechel and Vér, Komatsu, and Allard and Champoux. The independent variables of these methods are specific flow resistivity and material thickness. However, the existing literature fails to provide proper knowledge regarding the prediction accuracy of these methods. The aim of this study was to determine the prediction accuracy of the sound absorption coefficient of these seven published impedance prediction methods. The study focused on normal sound incidence. Accuracy was determined by comparing the predicted and the measured absorption coefficients of 82 mineral wool configurations. The transfer matrix method was used to calculate the absorption coefficient within 100 and 3150 Hz. Allard and Champoux’s method reached the best prediction accuracy. A simplification of this method was developed to enable fast implementation. The results are very useful for researchers and developers who employ impedance prediction methods.