Complex surface impedances and spherical wave approximations in image source models for outdoor auralization

Auralization of different traffic scenarios enables urban planners to predict the effects of soundscape interventions. For efficient calculation of the required impulse responses, geometrical acoustic methods are widely used, particularly in room acoustics simulation. For outdoor applications, however, it has been shown that the precise modeling of reflections is more critical than in room acoustics since the reflection density usually is significantly lower, so that the individual reflections have a more specific impact. This study incorporates complex surface impedances and the Weyl-Van der Pol equation to approximate spherical-wave reflections into the filter generation process of the image source model. The transfer functions generated by direct sound and reflected sound are compared to those which use real-valued, random-incidence absorption coefficients as typically used in geometrical acoustic applications. The improvement of the filter accuracy is discussed on the basis of reference measurements and in the context of traffic noise auralization.