Escolano-Carrasco J., Jacobsen F.

The Digital Waveguide Mesh (DWM) has become one of the most popular of the different physical modelling paradigms existing in the time domain. It consists of a recursive digital filter structure where a d’Alembert solution of the wave equation is propagated. One of the most attractive characteristics of this method is related to the simplicity of incorporating frequency dependent boundary conditions. Assuming that the reflecting surfaces are linear and time-invariant, their impedances (and thus their reflectances) can be simulated by means of digital filtering. So far, the digital filters have been designed to satisfy the reflection response associated with the impedance in the normal direction. However, the resulting model does not agree with an assumption of locally reacting surfaces, and this can give rise to contradictions in the physical interpretation of the reflected sound field. This paper analyses the behaviour of the frequency dependent boundary conditions in DWN in order to obtain a physical interpretation of the simulated impedance surfaces. The interpretation is validated by several examples.