The potential of additively manufactured porous absorbers in the design of multi-layer microperforated absorbers

Abstract

Microperforated absorbers (MPA) are a well-established technology for attenuating sound in flow carrying ducts. MPAs usually consist of a microperforated panel (MPP) in combination with a cavity as back volume. The damping maxima of MPAs occur in the range of their resonant frequencies and the effect is narrowband compared to porous or fibrous absorbers, which damp broadband at high frequencies. The resonant frequencies of MPAs decrease with increasing back volume. This provides a challenge, especially in applications with limited installation space when the damping of low frequencies is required. In the literature, the combination of MPPs and porous or fibrous absorbers is reported to reduce the required back volume. Therefore, double-layer MPAs with an additively manufactured porous absorber underneath the MPP are introduced in this work. The advantage of using additively manufactured porous absorbers as an acoustic metamaterial over conventional absorbers is that the acoustic properties can be specifically adapted to the required impedance boundary conditions. The results of this work show that the additively manufactured absorbers reduce the required back volume by up to 13% compared with liners without absorber underneath the MPP. Experimental validation underscores the robustness of the chosen design approach for double-layer MPAs.

Keywords

• microperforated absorber (mpa)
• acoustic liner
• acoustic metamaterial
• additively manufactured porous absorber
• microperforated panel (mpp)