Scale model experiments on the diffraction and scattering of sound by a partially rough curved surface

Scale model experiments have been conducted to study the propagation of sound over a curved surface partially covered with rigid random roughness elements in the high‐frequency diffraction/low‐frequency scattering regime. The effects of roughness are found by comparing the sound field with that obtained with a fully smooth curved surface. Experiments indicate that roughness in the shadow zone acts to tunnel more sound into the shadow zone of the partially rough surface, relative to the curved smooth surface, via a ‘‘creeping boundary wave.’’ This wave qualitatively follows the trends of both creeping waves due to diffraction and Tolstoy‐type ‘‘boundary waves’’ due to coherent scattering. However, roughness in the bright zone causes less sound to propagate into the shadow zone of the partially rough surface, relative to the curved smooth surface, because of incoherent scattering. [This work is supported by a Fannie and John Hertz Fellowship.] a)Current address: National Center for Physical Acoustics, University, MS 38677.