On the holes interaction and heterogeneity distribution effects on the acoustic properties of air-cavity backed perforated plates

Most of the available approaches used to model the acoustical behaviour of perforated plates are based on the assumption of no interaction effect between the holes. In practice, the holes are generally closely separated such that the interaction effect can affect their acoustical response. In this paper, the effects of holes interaction and heterogeneity distribution on the acoustic properties of air-cavity backed perforated plates are studied. The classical functions accounting for the holes interaction effects are theoretically reviewed and illustrated. An expression for the geometrical tortuosity, originally derived for granular materials, is used to properly account for both the holes interaction and heterogeneity distribution effects. This expression is integrated in the characteristic impedance expression following Atalla and Sgard [J Sound Vib 2007;303:195–208] model. Perforated plate specimens with different centre-to-centre holes distances (pitches) are built and tested using an impedance tube. It is particularly shown that in the presence of these effects, the resonance frequency is shifted towards the low frequency ranges without degradation of the absorption curve. These effects on the surface impedance and absorption coefficient are discussed in details. A very good agreement is observed between the simulation and the experiments.