Inverse acoustical characterization of porous material: A novel approach using diffuse sound field and transmission loss

Porous materials are largely used to improve sound quality in enclosed spaces. Inverse acoustical characterization of porous media is becoming popular due to experimental practicality. Most of the studies have as input data some impedance tube measurements. However, this approach presents several complications, mainly concerning the sample boundary conditions. The purpose of this study is to obtain the macroscopic parameters by inverse characterization, using transmission loss and the absorption coefficient as input data, both measured in reverberant chamber. One-piece and partitioned 2 m2 samples were measured. Several low-density materials were analyzed. The influence of boundary conditions, acoustic diffuse field and impervious screen layering porous material have been investigated. The Transfer Matrix Method is combined with the Johnson-Champoux-Allard equivalent fluid model on an optimization process. Transmission loss and absorption coefficient are simultaneously calculated. The mean square error between calculated and measured values is set as the objective function over the frequency range. Although the mounting condition of the measured transmission loss setup has required appropriate adjustment, good satisfactory repeatability on the optimized parameters was achieved.