ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06
1aPA10. An experimental investigation of the propagation of sound over a
flat rough surface of finite impedance.
James P. Chambers
James M. Sabatier
Natl. Ctr. for Phys. Acoust., Univ. of Mississippi, University, MS 38677
Recent work on rough surfaces by Medwin et al. [ 657--665 (1986)]
has indicated the presence of acoustic boundary waves in the fluid directly
above rough surfaces with high acoustic impedances. The effect of this boundary
wave is that the sound field above the rough surface is louder than it would
have been over a similarly smooth surface at close ranges due to multiple
coherent scattering. The opposite is true at longer ranges since the scattering
becomes incoherent. The ranges of coherent and incoherent scattering depend on
the roughness scale and frequency of the sound source. The experimental work
described above was performed over surfaces with high acoustic impedances such
as wax and steel. The purpose of this present work is to find out if similar
trends exist in the propagation of sound over rough surfaces that possess a
lower acoustic impedance. Sound signals will be measured above a rough surface
and compared to the signal above a smooth surface of the same material.
Preliminary experiments using Styrofoam indicate that similar trends exist
above the low impedance rough surface as did over the high impedance rough
surfaces. [Work supported by USDA.]