Acoustic properties of plates with unevenly distributed macroperforations backed by woven meshes.

A hybrid model describing the acoustic properties of plates with macroperforations that can be unevenly distributed on the plate surface and backed by woven or precision woven meshes with microscopic perforations is proposed. The plate perforations may be of circular or rectangular shapes. Since the perforated plate may not necessarily be considered as an equivalent fluid, its impedance is calculated by the Maa model [Noise Control Eng. J. 29, 77-84 (1987)], whereas the Johnson-Champoux-Allard model [J. Appl. Phys. 70, 1975-1979 (1991)] is used for the mesh, considered as an equivalent fluid. A simple model for the elementary cell of the mesh structure is proposed in order to calculate parameters that can be considered as the thermal characteristic length Λ' and the viscous characteristic length Λ. An effective airflow resistivity is introduced to account for the increase of particle velocity through the mesh placed behind the carrying macroperforated plate and is used in the transfer matrix approach to obtain the impedance of the whole multilayer system. The hybrid model seems to represent a good approach of this multilayer system. The theoretical predictions are compared with experimental measurements.