Sound diffraction over noise barriers with added devices installed on the top edge

Abstract

Airborne sound insulation index of the noise barrier panel and the sound absorption coefficient of the barrier surface are the acoustic parameters that are usually determined in specialized laboratories, however they can be also determined in situ. Acoustic characteristics of a barrier include also the diffraction index difference determined from comparison of barriers with plain top edges and barriers with added devices installed on the top edge. The index is determined from the impulse response values determined for the acoustic wave propagation path from the sound source to a set of properly distributed measurement points. By means of the same method, one can also determine the difference in a barrier's acoustic effectiveness between the plain top barrier structure and its version with added devices mounted on the top. The paper presents measurement results for three types of added devices mounted on the top edge of the barrier. The diffraction index differences have been determined for each added device type and the acoustic effectiveness for each device has been compared with the plain top edge acoustic barrier.