This study is mainly to discuss the influence on the absorption coefficient of porous materials by changing variety of material and air layers. First of all, this study derives some simplified models for both the absorption coefficient and the acoustics impedance when sound waves are transmitting through and reflected by porous media. Meanwhile, the variation of the absorption coefficient with frequency when the thickness of porous materials and air layers are changed is also discussed. The result of the study is clearly to show that the prediction on the absorption coefficient quite coincides with the measurement.
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