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The performance of a finite impedance wedge barrier

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The problem of sound screening by a wedge shaped barrier with general boundary conditions is considered. The theoretical methods used for evaluating the effectiveness of a noise barrier on the ground often appeal to one model for considering the wave reflection from the ground, and another model accounting for the wave diffraction at the top of the wedge barrier. For a point-like sound source, there are several attractive models for evaluating the sound field diffracted by either an ideally hard or an ideally soft wedge, but few treat the case of a wedge of more general surface boundary conditions. The purpose of the present work is to carry out a numerical investigation based on an existing diffraction model where the edge diffracted field is given as a high frequency asymptotic expression. The sound excitation source is taken as linear and parallel to the edge of the wedge, hence the two-dimensional character of the problem. The expression of the field diffracted by the edge of the absorbing wedge is adapted from a model where it is developed from the solution for plane wave incidence. More specifically, the solution to the case of the line source in that model is elaborated by considering a wave spectrum decomposition of a cylindrical wave. Numerical results of calculations on an absorbing wedge in free space show that the amplitude of the edge diffracted field increases with increasing hardness of the wedge. This field amplitude is also found to increase with an increasing value of the opening angle of the wedge, which is in agreement with the results for the case of an ideally hard wedge irradiated by a spherical source. Another point of interest, which is also considered in this study, is the case of a hard wedge on a ground with mixed boundary conditions, and which is considered for both the case of a point source and the case of a line source. Further examples are considered for predicting the insertion loss of an absorbing barrier in a typical road traffic situation. The barrier is erected on ground consisting of a combination of two grounds with different impedances, namely that of asphalt on the source side, and of grass on the receiver side. The results of numerical calculations show that the noise shielding performance of the impedance barrier diminishes both for increasing hardness of the barrier and for increasing value of the barrier angle. This latter conclusion is also in agreement with previous findings for a hard wedged barrier, with a point-like sound source. The divergence of the sound source is also found to have a minor effect on evaluating the effectiveness of the noise barrier.
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Keywords: 51.1; 76.1.1

Document Type: Research Article

Affiliations: Malmo University

Publication date: September 1, 2003

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