Search

Perforated plates are employed in various noise control applications to attenuate sound whose direction of propagation is normal to the plate. In certain instances this is accompanied by a bias flow through the perforations. The mechanism of sound attenuation is dependent both on the physical properties of the perforated plate and on the mixing of the small jets emerging from the perforations. The objective of this study is to analyze the acoustic properties of perforates and develop a comprehensive theoretical model that is capable of predicting the sound attenuation over a wide range of bias flow speeds, porosity, hole size, and thickness values of the perforated plate. The theoretical analysis of this investigation is validated through experimentation and comparison with existing models.As a first step in this work, a study has been conducted on the insertion loss of perforated plates at normal incidence without bias flow. The experiments comprised microphone measurements of insertion loss for eleven perforated plates that varied in thickness, hole size, and porosity. The theoretical model is based on planar wave propagation through a single contraction/expansion chamber, with modifications to account for hole interaction effects. The resulting formula for insertion loss yields superior predictions over past theories for the range of properties investigated. Deviations between experimental measurements and theoretical predictions of insertion loss are less than about 1.5 decibels for dimensionless hole diameter d/λ 0.25, the experimental measurements indicate a saturation, followed by a decrease in insertion loss due to increasing flow noise for plates with porosity β