Random and periodic square wave barriers in noise control

Abstract

Federal regulations and increased public interest in reducing transportation noise have led to the construction of miles of sound walls. Most of these walls are almost perfectly non-absorptive barriers with the shortest possible diffractive edge; a straight line. A number of alternate strategies have been studied in recent years, including T-top, Y-top and random edged barriers.Prior investigations by other researchers suggest that it might be possible to improve the performace of a barrier without increasing the average height by introducing a jagged profile. This is because the jagged geometry on the edge of a sound wall alters the sound pressure level in the shadow zone by causing the region of the barrier nearest the receiver to admit multiple paths with variable phase. The direct waves from the diffracting edges of the barrier and waves subsequently reflected from the ground plane are superposed at the receiver causing constructive or destructive interference at the receiver. This is not easily amenable to analytical methods. This led to anechoic chamber testing of the various practical jagged edge treatments. In this paper, theoretical and experimental investigation of the effectiveness of more practical random and square wave barriers are detailed. The TNCC Anechoic chamber experimental facility is utilized for one-sixth scaled barrier tests.