The Application of Transfer-Matrix Method on The Absorption of Micro-Perforated Panels and Perforated Panels Backing with Porous Materials

This study is mainly to discuss the sound absorption effects of mirco-perforated panels and perforated panels backing with porous materials when changing the diameters of the apertures,the perforation,the thickness of air layers,the thickness of backing materials and the flow resistivities of different materials.In order to analyze these two absorptive structures,assocating the transfer matrices of sound wave in different media,and we can get the formulas of surface impedances and sound absorption coefficients,and then we do experiments in the impenance tubes.It shows that the theory and the experiment result can match well. Finally, we change parameters of the sound absorptive structers and calculating the influence of the sound absorption coefficients from the theory.
There are some conclusions as follow:
1.For designing mirco-perforated panels,the diameter is 0.4mm,the perforation is 1％,the panel thickness is 1mm,and the larger air layer will get advance in sound absorption coefficients in low frequency and sound absorption bandwidth.

2.The double layer of the mirco-perforated panels will have better sound absorption effects and can broaden the frequency range of sound absorption.

3.For perforated panels backing with porous materials,because the porous materials have higher sound absorption coefficient in high frequency,we can adjust the structure parameter,ex: the diameters of the apertures,the perforation...etc,that can make structures have ideal sound absorption effects in both low and high frequency.

4.The perforation must be over 20％, and then the sound absorption have some level effect when perforated panels backing with porous materials.

5.The acoustic characteristic of the mirco-perforated panels is decided by the structure parameters of panels themselves,and when the diameters of the apertures are larger and over 20％, the acoustic characteristic is decided by the absorptive materials in air layer.