An experimental evaluation of noise reduction by scattering in low velocity ducts

This paper presents the results of an experimental assessment of both conventional absorption and Bragg scattering techniques for the reduction of noise transmission by a fan in a short, low velocity duct connecting two reverberant rooms. There are several advantages of using the scattering technique; for example, the saving of space and the facts that the device can be tuned to a particular frequency and that it is not necessary to use materials such as absorbent foams which can be a health hazard. The system appears to work equally well with externally generated sources of sound but the maximum attenuation with eight scatterers is found to be about 12 dB at the Bragg frequency.