This paper reports the results of normal incidence sound absorption measurements done over three different acoustic materials with varying thickness. A microperforated panel (MPP) was added to cover the absorber, in some cases leaving an air cavity between them. The measurements were done in an impedance tube, according to ISO 10534-2:1998. The aim was to find the best setup of the test samples to build a device that improves the absorption especially at low frequency. It is concluded that having the acoustic materials in contact with the MPP and backed by an air layer gives the expected results.

In this paper, an inverse acoustical characterization for determination of porosity, flow resistivity, tortuosity and other parameters of a concreted wood material was proposed. Sound absorption measurements for a concreted wood fiber material were made in an impedance tube. Four acoustical models from literature were briefly described. Each model was fitted to the experimental data in order to compute their unknown parameters. Using a least-square method, the experimental data (sound absorption coefficient) was used to optimize the acoustical models by best-fitting the unknown parameters. The results of this paper show that the presented technique leads to reliable estimates of the physical parameters of the material.