Generalized power law for predicting the air flow resistivity of thermocompressed fibrous materials and open cell foams

The compression of sound absorbing materials can change significantly their acoustical properties. It is commonly admitted that the air flow resistivity is the main parameter governing the acoustical efficiency. Several authors propose empirical laws to predict the resistivity as function of the compression rate. The models are based on a power function with a power related to the kind of material. In this paper, we propose a generalized power law to calculate the air flow resistivity of compressed porous materials with high porosity (⩾0.9). The power is here related to the material initial porosity. The influence of fibres orientation distribution is also addressed. The proposed formula shows a good agreement with the measurements performed on several types of porous materials (four fibrous materials and two open cell foams).