Low-frequency broadband sound absorption of micro-perforated panel absorber with different extended necks

A micro-perforated panel (MPP) absorber with extended necks is proposed to seek low-frequency efficient sound absorption in a deep sub-wavelength thickness. The effects of the extension direction and the design parameters of the extended necks on its sound absorption characteristics have shortcomings and are indeterminate, further affecting the application of combining multiple absorption cells. The theoretical model is formulated to account for the different extended necks: e.g. the outside extended necks, the inside extended necks, and the inside-outside extended necks. The sound absorption curves of the MPP absorbers with the different extended necks are theoretically and numerically analyzed. The length of the inside extended necks is more sensitive to the resonance frequency of the MPP absorber; also, its perforation diameter is more significant to the absorption peak. Additionally, the variation of the outer diameter of the inside extended necks and the thickness of the backed air cavity promotes the resonance frequency of the MPP absorbers to change, but its absorption peak and 0.5 absorption bandwidth remain unchanged. An experimental measurement is carried out to verify the results. This paper provides an exploration for a novel MPP absorber, alleviating the low-frequency sound absorption bandwidth and total thickness.