A double-layer acoustic absorber as potential substitute for traditional micro-perforated elements

Abstract

A double-layer fibre-less absorber is presented in this paper as possible substitute for Micro-Perforated Element (MPE), at least in room acoustics applications. This absorber is called Micro-Grooved-Element (MGE) since grooves are present on one of the contact surfaces of the two mating layers. These grooves generate a number of micro-channels when the element is assembled. Despite the necessity of having two layers, it is possible to have a certain control of the weight because the layers are provided with wide slits. The MGE offer the advantage of requiring basic manufacturing process (typically milling), instead of the less cost effective laser cut used for MPE. Substituting micro-perforation with engraving allows the generation of micro-apertures which are smaller in cross section and length than in case of traditional MPE, while it is still possible to preserve adequate porosity. In this work, the acoustic performance of MPE and MPE are tested and compared in terms of absorption coefficient and transfer impedance in both linear and non-linear regimes. In case of MGE, the presence of more minute apertures will result in an increase of the absorption coefficient up to ≈30%.