A compound microperforated panel backed by a panel-type resonator with a Helmholtz neck and multi-frequency resonators to improve bandwidth and low frequency sound absorption

The present study is aimed to develop a compact sound absorber structure that can simultaneously improve low frequency sound absorption performance and broaden the half-absorption bandwidth of a microperforated panel (MPP)-type structure. A novel structure is proposed by backing an MPP with a panel-type resonator incorporating a Helmholtz neck and multi-frequency resonators (PRHM) to form an MPP-PRHM compound sound absorbing structure. A fully coupled vibroacoustic model based on the modal coupling method is developed to predict the sound absorption characteristics of the proposed sound absorbing structure. The accuracy of the model is verified against the finite element model and experimental result. The mechanism forming the sound absorption characteristics of the compound structure is investigated, allowing the widening of bandwidth in the low frequency range. The experimental and numerical results have shown that the proposed PRHM structure is able to create two distinctive low frequency sound absorption peaks respectively attributed to Helmholtz resonance (due to the relatively in-phase relationship between air mass in PRHM neck and air particle in MPP perforation, which simultaneously enhanced the viscous losses in MPP perforation and PRHM neck) and structural resonance of PRHM (due to the relatively in-phase relationship with the velocity of air particle in MPP perforation). The experimental results demonstrated that a relatively wide bandwidth of 362 Hz was observed and the averaged absorption coefficient was improved by 650 % in the very low frequency range of 100 Hz to 150 Hz as compared to a single MPP structure.