Absorptive noise barrier on finite impedance ground.

Abstract

This paper describes a scheme to predict the performance of absorptive barriers on ground of finitea cousticali mpedance. The Fresnel-integraflorm of Macdonald's solution is used for the diffractionc alculation. The acoustical properties of the barrier surface, and of the ground on eithers ide of the barrier, a re specifiedi n terms of a nonparameter model based on specificf low resistance. F rom this one obtains the complex reflectiocno efficienatn d boundary-loss factor for sphericalw aves at each surface, which in turn are used to modify the amplitude and phase of each diffractedf ieldat the location of the receiver. The total fieldb ehind the barrier shows interferenceb etween the directf ieldo f the source and itsr eflectionast the ground on eithero r both sides of the barrier, and at the surfaceo f the barrier. The well-known predictions cheme of Maekawa (which does not allow for interference) gives resultsw hich are areasonable mean of values provided by the interferencet heory. It is shown that the insertionloss of barriers depends more significantloyn the type of ground, e.g. asphalt or grass, than it does on the absorptive properties of the barrier surface.