A method for measuring the acoustic properties of a porous sample mounted in a rigid ring in acoustic tubes

This study presents a method to measure the acoustic properties of a homogeneous porous material with a support or a reduction element in an acoustic tube. Some materials tested have a lateral size much smaller than the tube’s diameter, as they cannot be produced in the correct dimensions without corrupting the material; this also permits the testing of the same samples in a large frequency bandwidth by using different section tubes. Moreover, the acoustic leaks on the material boundaries can significantly change the transmission loss measured in tubes. To rectify these problems, rings can be placed on each material surface. The presence of these rings can influence the acoustic indicator measurement; while this effect is negligible for tubes with a large cross section, it is not for tubes with a small cross section. To correct, or remove, the influence of the rings, we propose to use an application of the parallel assembly process of the transfer matrix method, which has recently been proposed by Panneton et al. [Proceeding Internoise, New York (2012)]. Measurements on classical porous materials with and without reductions are proposed and compared to simulated results. The ring’s effects and the proposed corrections are discussed for different materials.