Directivity-based passive barrier for local control of low-frequency noise

This work concerns with improving the transmission loss offered by a noise barrier separating two acoustic spaces in the low-frequency range. A novel concept of local mitigation of the transmitted noise at a target receiver location is presented by controlling the directivity of the transmitted noise through a point mass attachment on the barrier surface. Mass attachment at an arbitrary location is shown to increase the noise transmission. Optimal locations of the mass to minimize the sound transmission in the normal, oblique and tangential directions to the barrier are obtained. Optimal placement of the mass results in a major transmission reduction around the target location, much more than achievable by a uniform distribution of the mass over the barrier. Total transmitted pressure is also reduced; however, local reduction around the target location is much higher. The effects of variation in the excitation frequency and magnitude of the attached mass are investigated.