S. T. Ho
I. J. Busch-Vishniac
Dept. of Mech. Eng., Univ. of Texas, Austin, TX 78712-1063
D. T. Blackstock
Univ. of Texas, Austin, TX 78713-8029
A preliminary model experiment showed that the insertion loss for a random edge barrier exceeded that of a straight edge barrier of the same average height [J. Acoust. Soc. Am. 97, 3392(A) (1995)]. Based on this promising result, a three-level full factorial model experiment has been conducted on random edge barriers. The top of the barrier is a strip of sheet metal of fixed average height but made randomly triangular by straight line cuts. A random number generator was used to specify the height variations (Delta)y (scaled to a prescribed maximum value) at fixed intervals (Delta)x along the barrier. Nine different random edges provide a range of 9--37 mm in (Delta)x and 5--18 mm in (Delta)y. An electric spark was the sound source, a 1/8-in. B&K condenser microphone the receiver. The frequency range of the measurements is 5--21 kHz, the Fresnel number range 2--20. In most of the measurements the random edge barriers showed 3--8 dB more insertion loss than the straight barrier. For several cases, however, the straight barrier was better. [Work supported by TxDOT.]