Effect of a porous absorbing layer on absorption characteristics of a double-leaf MPP space sound absorber

A micro-perforated panel (MPP) is usually placed in front of a rigid-back wall with an air-back cavity and forms a Helmholtz resonator with its holes and air-back cavity. However, the authors have so far proposed several kinds of MPP space sound absorber, which can absorb the sound energy without a rigid-back wall. A double-leaf MPP space absorber (DLMPP) is one of them, which is arranged with two MPPs in parallel without rigid-back wall. A DLMPP shows a peak absorption at the resonance frequency and additional absorption in a low frequency range. Therefore, a DLMPP can be used as a broadband space sound absorber in a practical situation. In this study, as an approach to improve its sound absorption performance, we propose a DLMPP with Porous which has a porous layer between two leaves of MPP, and its absorption characteristics are theoretically analyzed and discussed through the numerical examples. As a result, the absorption coefficient becomes 0.1…0.2 higher in all frequency ranges. The range of the resonance peak becomes broader. Thus, a porous layer can be said to improve the performance of a DLMPP.