Multi-layer perforated panel absorbers with oblique perforations

Abstract

Many different solutions exist to improve the low-frequency sound absorption performance of acoustic resonators, extending or coiling up space into the resonator being some of the most widespread. In this context, modern additive manufacturing processes pose a new scenario in which these devices can be engineered to yield outstanding acoustic properties. In a recent work by the authors, a solution consisting of a perforated panel with oblique perforations was analyzed, results showing an enhanced sound absorption performance when compared to traditional perforated panel absorbers. This technical note aims to show the potential of these panels when used in multi-layer arrangements both to widen their effective sound absorption bandwidth and to improve their low-frequency performance. A simplified approach that relies on the fluid-equivalent theory was used together with the Transfer Matrix Method (TMM) to analyse different configurations, prediction results showing a good agreement when compared to experiments in an impedance tube over additive manufactured samples. Unlike other perforated-based solutions, the proposed system avoids addressing the cavity design while showing improved sound absorption features.