On the Shielding of Noise Outdoors

Abstract

Shielding of noise by buildings and walls can serve very usefully in the control of noise in communities. Fehr has reported a method, derived from diffraction theory, for computing the insertion loss of an impervious wall of infinite length and arbitrary height, placed between a point source and point receiver at arbitrary distances from the wall. Hayhurst has reported measurements on shielding by walls up to forty feet high, using stationary aircraft as noise sources. This paper presents further measurements on shielding by structures outdoors and attempts to correlate the available results with theory. In practice one must take into account, in addition to the idealized diffraction from an infinite shield, several factors including (a) finite size and detailed geometry of the shielding structure; (b) radiation from the ground image of the noise source; (c) attenuation contributed by the terrain, with and without the shield interposed; (d) refraction, scattering, and shadow effects caused by wind and temperature gradients and by turbulence. Studies of these effects have been made and procedures for estimating the amount of shielding obtainable in certain practical cases will be reported.