Acoustic response of fibrous absorbent materials to impulsive transient excitations

The parameters used to characterize the acoustic behaviour of fibrous absorbent materials are usually the complex characteristic impedance and the complex wavenumber, which permit the calculation of the airflow resistance and vice versa. Different methods have been satisfactorily used by other authors in order to perform this characterization on the basis of a macroscopic modelling of the behaviour of these materials. In this paper, the suitability of this approach for predicting the acoustic response of absorbent materials to impulsive excitations is evaluated. The constant term of the airflow resistance equation for absorbent materials with different densities is quantified by means of a modified version of the impulse method. These values are then incorporated into one-dimensional acoustic calculations in order to predict the response of absorbing materials to pressure pulse excitation. The very good concordance observed between calculated and measured reflection and transmission coefficients shows the suitability of the proposed procedure for the characterization of absorbent materials.