Suppression of diffracted sound by green walls

Green walls covered with vegetation are used in urban areas to purify the air, improve the appearance of the landscape and reduce heat-island effects. They also improve the noise environment. It has been reported in previous studies that the surfaces of green walls have good sound-absorbing performance. However, the contribution of the greenery to the sound-insulation performance of green walls, which are also used as noise barriers, has not been verified quantitatively. In this study, the enhancement of the sound-absorption performance of a wall due to greening was verified via measurements using actual green walls and the results were compared with those of a steel noise barrier, which has limited sound-absorption performance. Numerical analyses using the boundary element method (BEM) were also conducted. As a result, it was confirmed that the sound-absorbing effect generated by wall greening reduces the diffracted noise, thus contributing to sound-insulation performance enhancement in areas above the noise barrier.