Reduction Effects of Shaped Noise Barrier for Reflected Sound

Abstract

Noise Barriers are widely installed to control the propagation of vehicle noise from highway. However, the installation may result in a secondary noise caused by reflection, especially, if there exists a residential area on the opposite side. Hence, to effectively use noise barrier, it is mandatory to first predict the noise sources taking place on the roadsides and to apply the findings afterwards. In this study, by evaluating the reduction effects of reflection noise according to different panel shapes including wing, zigzag and curved type, the optimal soundproof panel shape and design factor that can minimize the reflection noise are suggested. The sound reduction was modeled by general linear model for the case of zigzag and curved shape with nominal variances. To simulate the effects of each shape, Nord 2000 with sound traveling model was used. As a result, all panel types have shown reduction effects on reflected sound, with maximum of 2.2 dB for zigzag and 1.2 dB for curved shapes. The designing factors had impact on the density of zigzag type and on the degree of bending in the curved shape. Specifically, for first noise level (up to 5 story building), reduction effect is improved for smaller size of wing type, wider angle between zigzag type panels and gentle slope of curved type. Overall, curved noise barrier labeled as C-9 is found to be the best in diminishing reflection noise. This type of barrier can be effectively used to control damages caused by reflection noise at downtown region, where extent of traffic is increasing from day to day.