Broadband and low-frequency sound absorption of modified Helmholtz resonator combined with porous layer addition

In this work, a hybrid acoustic material (HAM) is designed for broadband and low-frequency sound absorption based on the combination of two different materials: a porous layer (melamine foam) and a modified Helmholtz resonator with embedded necks (HRENs). Theoretical predictions, numerical simulations, and experimental measurements are conducted to investigate the acoustic characteristics of the HREN. The HAM absorption mechanism is presented to evaluate the broadband sound absorption by the impedance matching effect of the different structures. The results of experimental tests confirmed that the HAM has broadband sound absorption and presented good agreement with an equivalent fluid model and numerical simulations. Broadband sound absorption was comparatively evaluated by the broadband factor (Qα), revealing the advantages due to the possible configurations of HAM in relation to HREN and melamine foam. In addition, the selection and dimensions of the HREN holes and the perforation ratio, in the range of 3%–10%, allow the hybrid sound absorber to achieve one absorption peak between 235 and 582 Hz with quasi-total absorption (α≥0.8). This work contributes to the understanding of sound wave propagation and broadband absorption in acoustic materials composed of different materials combined.