Effects of compression on the sound absorption of fibrous materials

During the compression of a fibrous mat, it is well known that the absorption properties are decreasing. In order to predict this change, some heuristic formulae are proposed which take into account the modifications of the physical parameters (porosity, resistivity, tortuosity and shape factors) which enter the standard “equivalent fluid” model. Numerical predictions are then discussed and compared to experimental data obtained on a fibrous material (uncompressed and then compressed) used in the automotive industry.