Steve Ho
Ilene J. Busch-Vishniac
David T. Blackstock
Dept. of Mech. Eng., University of Texas, Austin, TX 78712-1063
In normal design the top edge of a noise barrier is straight. As a result, noise diffracted from the barrier edge seems to come from a string of highly correlated point sources, that is, a straight line source. The coherence of the diffracted sound therefore limits the effectiveness of the barrier. One way to spoil the coherence of the diffracted sound, and thus increase the barrier's insertion loss, is to vary the barrier height by making the top edge irregular instead of straight. The radiations from the point sources at the edge then are not well correlated. We have conducted preliminary experiments using physical scale models with random edge profiles. The spacing between height transitions and the height variation maxima are scaled to the wavelength at which the sound source (a spark) has a peak in its spectrum. Results to date show significant improvement (3--8 dB) for a barrier with a random edge profile compared to one of the same average height with a straight edge. [Work supported by TxDOT.]