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A theory for the propagation of sound in a resistive porous material is formulated in terms of the bulk elastic properties of the structure of the porous material and the permeating fluid. Impedance relations are developed to describe the acoustic behavior of porous material layers of finite thickness. The acoustic behavior of resistive screens and impervious septa is also characterized. An analytical procedure is outlined for evaluating the sound absorption characteristics of different coating configurations consisting of arrangements of porous material layers, impervious septa, and resistive screens. A novel design configuration is described that achieves optimal sound absorption levels at low frequency in air. The coating is lightweight and also thin in comparison with an equivalent layer of uniform absorbing material. The dynamic behavior of the design is explained in physical terms.
Moore et al. (Wed,) studied this question.