In situ characterization of wall linings with perforated facings

The in-situ characterization of acoustic materials is one of the main challenges in room acoustics. Previously, the characterization of a single porous layer backed by a hard wall was successfully done by combining pressure-velocity measurements near the surface of the material with an impedance model fitting approach. In practice however, many porous materials are mounted behind a membrane or a rigid perforated facing.
By again combining pressure-velocity measurements and a model fitting procedure, this work studies the possibility to characterize such systems. This was done by measuring a variety of perforated facings and membrane facings, whether in front of an air cavity or backed by a porous layer and com-paring the obtained impedance model parameters to the reference values. Good agreement was observed between the retrieved parameters and the references, with error in retrieved moving mass, facing thickness, cavity depth, porous layer thickness and porous layer flow resistivity not exceeding 15%.