Road noise barriers as sound radiation systems

Abstract

Road traffic noise has become a significant societal problem and the noise barrier as one remedy is studied acoustically. Traditionally, as a theoretical background for installing the noise barrier, the diffraction theory of the acoustic wave by a screen has been employed. In this paper, however, the noise barrier and the road structure on which a vehicle is a noise source are treated as one acoustic radiating system. By means of the boundary element method useful for an open-region problem, a two dimensional analysis is carried out. From the results of the analysis with the cross-sectional shape of the noise barrier and the frequency as parameters, it is found that a resonance is generated for a shape with parallel faces and the noise may be spread a large distance away in conjunction with the diffraction at the edge of the noise barrier. If an unrealistic containment is not expected and a horn shape is employed, the noise can be radiated upward in the direction normal to the road surface and the diffraction does not become significant. The frequencies studied were 150 to 300 Hz which are bothersome to the human ears.