SOUND FIELD DIFFUSIVITY AT THE TOP SURFACE OF SCHROEDER DIFFUSER BARRIERS

Reactive barriers are one of the most promising and novel environmental noise barriers. in this caseusing schroeder diffusers (e.g. quadratic residue diffusers) on the top surface of the t-shape barrier wasshown to significantly improve the performance of absorbent t-shape barriers. the reasons behind thehigh performance of diffuser barriers are considered in this investigation. a question about thediffusivity behavior of schroeder diffusers when they are utilized on the top of barrier was raised.diffusion coefficients of a diffuser in different conditions at some receiver locations were predicted byusing a 2d boundary element method. it was found that the diffusion coefficient of diffuser at the top ofbarrier is so small that the diffusivity of the structure is almost the same as rigid t-shape barrier. to findthe barrier’s cap behavior, the total field above the top surface of profile barriers was also predicted. itwas found that the lowest total energy is at the receiver side of the cap very close to the top surface,which could demonstrate the effect of top surface on absorbing the energy as wave transfers from sourceedge toward the receiver side of the cap. in this case the amount of minimum total energy depends on thefrequency and the configuration of the top surface. a comparison between the reductions of total field atthe source side of the cap with the improvements of barrier’s performance was also done. it was shownthat the amount of decrease in total field compared to that of an absorbent barrier “ref” is directlyassociated to the amount of improvement in the insertion loss made by the diffuser barrier compared tothe “ref” barrier in the wide area on the ground at the shadow zone. finally it was concluded that thediffuser on the top of barrier does not act as a diffuser and a kind of similarity between the contributionof diffuser and absorbent material on the top of t-profile barrier is seen.