Abstract:

The performance of a jagged-edge noise barrier (thin, infinitely long) is investigated numerically. The source is a spherical N wave. The theoretical approach is to treat the incident field in the plane above the barrier as a plane piston radiator (Kirchhoff approximation). Numerical calculation gives the radiated field (pressure time waveform) at any point in the shadow zone. A discrete Fourier transform then yields the spectrum. The numerical result for a straight barrier compares favorably with the asymptotic result of U. J. Kurze [J. Acoust. Soc. Am. 55, 504--518 (1974)]. Because of the intrinsic limitation imposed by the Kirchhoff approximation, however, the numerical method does not give accurate results when the listener is deep in the shadow zone. For the jagged-edge barrier, the numerical simulation confirms the experimental findings of Ho et al. [J. Acoust. Soc. Am. 101 (to be published 1997)] in that making the barrier edge jagged (1) increases the insertion loss at high frequencies, but (2) degrades the performance somewhat at low frequencies. Suggestions for improving the insertion loss formula of Ho et al. for a jagged-edge barrier are also made. [Work supported by the Texas Advanced Technology Program.]