Performance of absorptive treatments for single highway noise barriers

This research developed, analyzed, examined the use of sound-absorbing materials, used an algorithm and the sample problem to predict the L;Absorptive single barrier attentuation solution is obtained for the problem of diffraction of a plane wave sound source by a semi-infinite plane. A finite region in the vicinity of the edge has a highly absorbing boundary condition; the remaining portion of the half plane is rigid (hard). The problem which is solved is a mathematical model for a hard barrier with an absorbing edge. If the wavelength of the sound is much smaller than the length scale associated with the barrier, the diffraction process is governed to all intents and purposes by the solution to a standard problem of diffraction by a semi-infinite hard plane with an absorbent edge. Under the above approximations a mathematical model for a rigid barrier with a highly absorbing edge is given by a standard problem of diffraction by a semi-infinite rigid half-plane with a highly absorbing edge. The aim here is to solve this mixed boundary value problem. It is concluded that the absorbing material that comprises the edge need only be of the order of a wavelength long to have approximately the same effect, on the sound attenuation in the shadow side of the barrier, as a completely absorbent barrier.;Traffic noise is composed of thousands of sources with varying frequency content. To simplify noise predictions when barriers are present, an effective frequency of 550 Hz may be used to represent all vehicles. Also, the wavelength of sound at f = 550 Hz for traffic noise is about 2 feet.;According to the above conclusion, an absorptive highway noise barrier is only needed to cover approximately a 2 foot length of absorbing material. It would be more economical to cover only the region in the immediate vicinity of the edge with highly sound absorbent material.