Experimental study of the diffracted sound field around jagged edge noise barriers

Abstract

Noise barriers are commonly used to protect communities from transportation noise. In the present study, three types of barriers, modeled as half planes, have been tested in the laboratory: a conventional rigid barrier with a straight top edge, a straight top edge barrier covered with sound absorbing material, and a rigid barrier with a jagged top edge. Measurements were taken not just behind the barriers, but around them on a plane perpendicular to their top edge. Measured signals were compared against theoretical predictions contributing to further validation of a theoretical model. The sound absorbing material was found to affect the diffracted field more in the front of the barrier than behind it. The diffracted field in front of a jagged edge barrier, similar to the field behind it, was found to depend on the geometry of the edge in the area where the shortest diffraction path intersects the edge profile. Last, the performance of the three barriers was compared with one another in all areas around the barrier. It was found that the jagged edge barrier provides shielding similar to the sound absorbing barrier but at a fraction of the cost.

Use of Noise Barriers for Helicopter Noise Mitigation

“…In the following we show some comparisons between results obtained by the outlined prediction tool with experimental data. Figure 2 shows the good agreement of results obtained by DLSM for diffraction of a spherical wave incident on a rigid half plane, with laboratory experiments performed with a spark source as the noise source and a aluminum barrier with interchangeable top edges supported by plywood [2]. DLSM yields good results for both straight and jagged top edges.…”

“…For modeling the diffraction from the top edge of the barrier, the DLSM (Directive Line Source Model) [1][2][3] has been employed. According to DLSM, the problem of diffraction is transformed into a radiation problem from directive point sources continuously distributed along the edge of the barrier.…”

Fast Time-Domain Edge-Diffraction Calculations for Interactive Acoustic Simulations

“…subdivision into evenly sized segments [9,10]. 2 A third method, which is a hybrid of these two, was proposed in a simpler form in [10], and the remainder of this paper describes the implementation and the evaluation of a more robust form of that method.…”

“…Edge-diffraction impulse responses (IRs) are useful for acoustic simulations involving objects or environments comprising faceted surfaces and have been applied to many problems in acoustics such as loudspeaker radiation [1], noise-barrier analysis [2], and room-acoustics modeling [3]. Diffraction calculations correct for the high-frequency approximation inherent in modeling techniques based on geometrical-acoustics (GA) assumptions, allow for the modeling of sound propagation around occluders and into shadow zones, and provide a smooth, continuous soundfield at specular-zone and shadow-zone boundaries when combined with GA components.…”

Measurement and modeling of diffraction from an edge of a thin panel

“…Li and Clay [12], Chambers and Berthelot [13], and Menounou and You [14] presented comparisons between measurements and Medwin's BTM formulation, all three using a spark source as the acoustic source. Spark sources tend to produce little low frequency energy 1 , and thus the requirement of rigid wedge faces for the BTM solution is more easily met with common materials such as plasterboard, plywood, and aluminum used in these experiments.…”