ABSTRACT
Broadband sound absorption performance and high mechanical strength are major concerns for designing a microperforated plate (MPP) absorber, which is generally difficult to achieve for a single-layer MPP with straight holes. A MPP was proposed with variable cross-sectional holes, including large dents on one side, grooves on the other side, and intermediate micro-slits. The beneficial effects of the special geometrical features are thoroughly discussed and experimentally validated. Models to calculate the acoustic impedance are established, and acoustic behaviors within holes are simulated. It was found that the micro-slits could provide necessary acoustic resistance for impedance matching and very low reactance to expand sound absorption bandwidth. The large dents or grooves could provide the necessary thickness with negligible acoustic impedance to enhance plate mechanical strength. This research helps to implement a single-layer MPP design with good acoustical and mechanical performance.
ABSTRACT
An additional length model is usually used to describe the reactive part of the impedance end correction of microperforated panels, which is extended to describe the resistive part. The cross-sectional impedance is computed along the axis of one perforation cell with a circular hole. Except for the obvious jumps in the narrow regions at the inlet and outlet of the perforation, the impedance varies linearly along the axis following exactly that of the viscous wave in the circular hole. The additional length for the impedance end correction is obtained by extrapolating the linearly varying impedance inside the hole. Empirical models for the resistive and reactive additional lengths are obtained based on the thermoviscous acoustic simulation with 96 test cases. Within an error of about 10%, a unified additional length model is presented for both the resistive and reactive parts of the impedance end correction. Comparison with other existing models shows the accuracy of the proposed model.