Rectangular extended neck Helmholtz resonant acoustic structure for low frequency broadband sound absorption

Abstract

The Helmholtz resonant structure with a rectangular extended neck is designed in this work to solve the low-frequency broadband sound absorption problem. Theoretical and finite element absorption models have been established and are used for low-frequency acoustic design. What makes it interesting is that all parameters of the rectangular extended neck Helmholtz resonator can be adjusted to shift the working frequency. Four coupling structures with different neck depths, neck opening areas, cavity cross-sectional areas, and cavity depths are respectively designed. Each of these structures exhibits multiple sound absorption coefficient peaks to enhance the low-frequency absorption capacity. The effectiveness of the coupling structure is further analyzed by examining the broadband acoustic absorption mechanism based on the particle vibration velocity distribution. It is found that cells with different acoustic impedance contribute differently to the sound absorption, and cells with longer necks provide better noise reduction at low frequencies. The experiment is verified in the impedance tube, and the result shows that the coupling structure with 9 cells and a cavity depth of only 4cm achieves an average sound absorption coefficient above 0.8 at 210-340 Hz, thus verifying the accuracy of the theoretical model. Overall, the Helmholtz resonant cavity acoustic structure with a rectangular extended neck proposed in this study has a simple structure with low-frequency broadband acoustic absorption performance, providing a new approach for designing low-frequency broadband acoustic structures.