Propagation over rough finite impedance boundaries

Previous studies of the boundary wave associated with near‐grazing propagation over randomly rough surfaces have been concerned with high‐frequency (2.5–30 kHz) pulses and acoustically rigid surfaces [see, for example, Medwin et al., J. Acoust. Soc. Am. 66, 1131–1134 (1979)]. Continuous wave measurements of the excess attenuation spectrum by means of maximum length sequence signal analysis have been carried out. These have enabled study of roughness effects in the frequency range 500 to 2500 Hz. Data have been obtained over rough wooden surfaces and over a thin polymer foam layer to which rectangular 3 cm by 0.5 cm strips have been attached. These data have been compared with predictions due to Howe [J. Sound Vib. 98, 83–94 (1985)] modified for effects of roughness shape according to Tolstoy [J. Acoust. Soc. Am. 66, 1135–1143 (1989)]. [Work supported by S.E.R.C. (UK).]