Effects of diffusion on the sound propagation in a street

Abstract

Inter-noise 2004, 33rd International Congress and Exposition on Noise Control Engineering, PRAGUE, TCHÈQUE, RÉPUBLIQUE, 22-/08/2004 - 25/08/2004Many investigations have been carried out regarding sound propagation in urban streets. In most of them, multiple diffuse reflections by building façades are considered to be one of the most important effects on the sound propagation in streets. For instance, in a recent paper, J Kang has realized a systematic comparison between the sound level and reverberation time in urban streets resulting from diffusely (according to a Lambert's law) and geometrically reflecting boundaries, and has shown considerable differences. However, except for the Lambert's law, no result was given considering more complicated or realistic reflection laws. In order to evaluate the effect of diffusion for several reflection laws, a numerical model of sound propagation in a street was developed using the concept of sound particles. In this model, the building façades are defined by an absorption coefficient, a diffusion coefficient and a specific reflection law (specular, Lambert, uniform, "semi-diffuse" including the size and distribution of building façade irregularities). In this way, and using Monte Carlo methods, it allows simulating any type of reflection laws. Numerical simulations were then carried out, in order to compare the sound level and the reverberation time in the street for several reflection laws. As expected, these simulations show that the sound propagation in a street is function of the boundary conditions