Optimum attenuation of low frequency noise by proper tuning of a prismatic array of waveguides

Abstract An open, prism-shaped network of rigid strips can constitute an effective sound barrier for long wavelength sounds [1]. Its physical parameters may be chosen so that the delaying strip medium is perfectly matched to the particular frequency of the noisiest component of the incident sound. The phase lag introduced by the delay medium over free space propagation may then, with a few strips, reach a 180° value creating dipole line-sources below the prism vertex line-source, which cancel the low-frequency diffraction above the obstacle, thus protecting areas behing this barrier. This study deals with the evaluation of three theories which are likely to predict, for various 1 10 scale models the first stopband frequency where 180° phase lag is most easily obtained.