Enhanced low- to mid-frequency sound absorption using parallel-arranged perforated plates with extended tubes and porous material

Porous sound absorptive material (PSAM) and micro-perforated plate (MPP) limited by space are weak in absorbing low- to mid- frequency noise. In order to improve sound absorption in 100-1600 Hz, a compound sound absorber comprised of perforated plates with extended tubes (PPET) and a PSAM is proposed in this paper. A theoretical model is described to predict the sound absorption coefficients of two combinations: one has three parallel-arranged PPETs and a PSAM layer; the other one has two parallel-arranged PPETs, an MPP and a PSAM layer. The calculated results are then validated by the results measured in an impedance tube. The proposed combinations demonstrate superior sound absorption performance over more than three octaves in the targeted frequency range.