Simple prediction method for sound propagation behind edge-modified barriers

Abstract

In this paper, we describe a method for predicting sound propagation behind barriers with an acoustical device mounted on their top edge to reduce the diffracted sound. The sound-reduction efficiency of the edge-modified noise barrier was investigated previously with a sound source and a receiver located along a circular arc around the barrier top. It was reported that the efficiency is determined as a function of the angles of the source and the receiver, and that it is independent of their radii. On the basis of this finding, a procedure of predicting the diffracted sound field behind an edge-modified noise barrier is proposed in this paper. The prediction of sound propagation is simply modeled by the sum of multiple paths, which idealize interference due to ground reflection, and the angle-dependent efficiency of the edge device is applied to each path. The efficiencies of absorptive and pressure-release devices are determined by scale-model experiments, and the results are substituted into the prediction model. In comparison with the two-dimensional boundary element analyses, it is shown that the proposed procedure predicts the diffracted sound field precisely, including both the interference by ground reflection and the effect of the edge device.