Insertion loss of absorbent barriers on ground

This paper presents a method for calculating the insertion loss (IL) of a thin barrier covered with absorbent material, either on the source side, on the receiver side, or on both sides. The method used combines a classical theory for the propagation of sound over ground with an approximate solution for diffraction around an absorbent barrier, which can take into account the specific impedance of each side of the barrier. The validity of the method was confirmed by comparing theoretical results with experimental measurements for various geometrical configurations and screen boundary conditions. The results show that, when the angles of diffraction are significant, the insertion loss (IL) of a hard barrier can be substantially increased by covering one of its surfaces with an absorbent material. This absorbent layer must be placed on the surface of the barrier associated with the greatest angle of the diffracted rays paths (source top-edge or receiver top-edge). When these angles are about the same on each side of the barrier, the increase will be the same if the absorbent material is placed on the source or on the receiver side. In this case, by covering both sides of the barrier, the increase of the IL due to the absorbent will double compared to a single covering.