Acoustic propagation over periodic and quasi-periodic rough surfaces

Transport noise is an ever present concern in urban areas affecting the quality of life for millions of people. The traditional noise barrier is not always a convenient method of noise control and can divide communities. As a result, other types of barrier have been sought. Considerable interest has been devoted to the use of arrays of vertical cylinders1-3 especially as a result of the publication of the measured transmission spectra of a minimalist sculpture4. A particular advantage in using such arrays instead of conventional noise barriers is that they are relatively transparent and could be formed from natural means such as trees. However, such arrays do still present a barrier to pedestrian movement. Another approach is to use arrays of cylinders arranged horizontally on grounds near the noise source, the advantage being that they would allow greater pedestrian access and would be less intrusive. Such arrays effectively introduce a roughness to the ground, which is known to have a significant influence on near-grazing sound propagation5. Here we present a theoretical and experimental investigation of this influence on sound propagation and its potential for transport noise reduction.