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

A double-layer fibre-less absorber is presented in this paper as possible substitute for Micro-Perforated Element (MPE), at least in room acoustic applications. This absorber is called Micro-Grooved-Element (MGE) and it is based on the presence of internal micro-channels generated 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 slots. The MGE offers the advantage of requiring basic manufacturing process (typically milling), instead of the less cost effective laser cut used for MPE. Nevertheless, the design of these elements allows the generation of micro-apertures which are smaller in cross section and length than in case of traditional MPE, while still preserving adequate porosity. In this work, the acoustic behaviour of several MPE and MPE samples is studied. The absorption coefficients and the transfer impedances, in both linear and non-linear regimes, are compared. In case of MGE, the presence of more minute apertures results in a substantial increase of the absorption coefficient.