Derivation of time-domain impedance boundary conditions based on in-situ surface measurement and model fitting

Abstract

In order to achieve accurate time-domain wave-based simulations of a real room, the acoustical properties of the locally reacting materials within the room have to be implemented as time-domain impedance boundary conditions (TDIBC), in such a way that the behavior of the materials is well-simulated within the wave-based solver. This paper presents the implementation of such TDIBCs of two materials: a porous absorber and an acoustic carpet. Firstly, the material properties were measured both in the impedance tube and in-situ with a pressure-velocity sensor. Advantages and drawbacks experienced with both methods in this context will be presented. Next, the measurement results were fitted to broadband impedance models to extend impedance data to the lower frequency range (20 Hz-300 Hz), resulting in broadband impedance data (20 Hz-4000 Hz). Finally the TDIBCs, in the form of complex reflection coefficients, were fitted as discrete sums of rational functions