Acoustical characterization of perforated facings.

An experimental method to estimate the acoustical parameters of perforated facings used for noise control applications is proposed. These perforating facings (also called screens) can be woven or non-woven fabrics or even micro-perforated plates (MPP). Following the work by Atalla and Sgard [J. Sound Vib. 303, 195-208 (2007)], the perforated facings are modeled as porous media composed with identical cylindrical perforations of circular cross-section. The acoustical parameters characterized with the proposed method are the radius of the perforations and the perforation rate (also named the open-porosity). These parameters are obtained from analytical expressions and a single measurement of the normal acoustic surface impedance of the perforated facing backed by an air cavity in a standing wave tube. The value of the static air flow resistivity can also be recovered with no additional assumption or measurement. In the case of a facing that contains perforations of an arbitrary shape, the radius parameter should be understood as a characteristic length of the visco-inertial dissipative effects. Results for two characterization examples (a low porosity screen and a high porosity one) are presented and discussed. Values of the estimated static air flow resistivity are compared with the results from direct measurements. Values of the predicted sound absorption coefficients are compared to the measured ones.

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