High resolution sound absorption mapping with a PU surface impedance method

The in-situ surface impedance method with pressure-velocity probes is documented in many publications. The method is based on the measurement of sound pressure P and particle velocity U close to an acoustic absorbing material. A loudspeaker at a defined distance is used to generate a sound field with a known radiation impedance. The impedance of a small area (a few square centimeters) with a known impedance is scanned with an ultra-miniature PU probe very close to the surface. The area is made of steel with a cut-out, and behind this, a material with a known impedance is placed. In this paper the method is explained, the spatial accuracy of the measurement is examined and a visualization technique is presented with a display of the spatial distribution (2D picture) of the damping properties as a function of frequency.