Sound field diffusivity at the top surface of schroeder diffuser barriers
It has been shown in several studies that the T-shape profile barriers are one of the most successful noise barriers among many different profiles (May and Osman 1980; Hajek and Blaney 1984; Hothersall et al., 1991). In this case, it is shown by author (Monazzam and Lam, 2005) that in the same dimension, the T-shape profile has the highest performance compared to other profiled noise barriers. It was also shown both in that paper and in numerous previous investigations that covering the top surface with absorbent material improves the performance of the T-profile barrier significantly (Hothersall et al., 1991; Fujiwara and Furuta, 1991). Furthermore it was shown that using quadratic residue diffusers on the top surface of the T-shape barrier increases the performance of absorbent T-shape barriers in their frequency bandwidth significantly (Monazzam and Lam, 2005). It was also illustrated that using Schroeder diffusers on the top of T-shaped barriers shows better performance than that of any other used profile barrier compared with their equivalent absorbent barrier. The initial thought for implementing Schroeder diffusers at the top surface of the T-profile barriers was about the ability of Schroeder diffuser to scatter the energy at different angles. The type of diffuser, which have been most exploited in this investigation is the so-called Quadratic Residue Diffuser (QRD). The QRD design philosophy is one of attempting uniform scattering at different angles over a semi-circle. Based on this knowledge one would expect to redirect some of the energy flowing into the shadow zone at a different angles above the top surface of the barriers. If this happens, the energy flows to the shadow zone will be smaller and, consequently, the performance of the barrier will be improved.