Contributions by Richard Raspet on two aspects of the acoustics of rigid framed porous media

Two papers co-authored by Richard Raspet are about the surface impedance of grounds with exponential porosity profiles [R. Raspet and J. M. Sabatier, J. Acoust. Soc. Am. 99, 147–152 (1996)] and sound propagation in porous media containing main capillary pores with smaller pores in their walls [W. P. Arnott, J. M. Sabatier, and R. Raspet, J. Acoust. Soc. Am. 90, 3299–3306 (1991)]. The variable porosity ground impedance model enables better fits to outdoor short-range measurements over many types of grassland than the widely used semi-empirical single parameter model. Moreover, it has been found to represent the surface impedance of artificial surfaces such as felt. The theory for pores with porous walls which was developed in the context of thermoacoustic stack designs is the forerunner of several designs involving slit like pores with microporous walls, sinusoidal walls or periodically varying widths in the somewhat different context of creating useful sound absorbers by additive manufacture.