Aalto Acoustics Lab

Sound Scattering from Finite and Rigid Plates under Grazing Incidence

The formation and early evolution of acoustic scattering from finite rigid and porous samples are investigated under grazing-incidence excitation. The measurements are done in an anechoic chamber using a moving microphone over a planar aperture perpendicular to the surface.

Description

Sound propagation at near-grazing incidence near air-porous absorber boundaries remains an open experimental challenge. Previous investigations have reported apparent variations in sound speed near such interfaces, often based on analyses of the total sound field. We have studied sound propagation using spatially resolved microphone array measurements as well as moving a microphone in a grid close to the surface. The analysis of measurement is based on sound field separation to different components. While analyses of the total sound field reproduce apparent propagation speed variations reported in earlier studies, our results obtained from the isolated direct sound field indicate that the propagation speed of the directly arriving wavefront remains constant, with no evidence of physical wave bending toward the boundary.