Broaden the sound absorption band by using micro-perforated plate back cavities with different cross-sectional areas

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.

Section: Introductionmentioning

confidence: 99%

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

Yan,

Wu,

Zhang

et al. 2024

“…Limited by the law of mass action and causality constraint, low-frequency broadband noise reduction has always been a hot and difficult issue in the field of noise control [1][2][3]. Although traditional sound absorption/ insulation materials have been widely used in the engineering field, large and bulky acoustic structures are often required for low-frequency and broadband noise, which seriously limited their applications in noise control [4][5][6]. Therefore, the emergence of acoustic metamaterials with small size control large wavelengths brings new directions for low frequency broadband noise control [7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Study on the acoustic performance of bending metasurface with ultra-thin broadband quasi-perfect sound absorption

Cheng,

Zeng,

Liu

et al. 2023

In order to achieve low-frequency broadband noise control under subwavelength thickness, this paper established a theoretical model for calculating the sound absorption coefficient of curled acoustic metasurface (CAM) composed of embedded hole, equal width curled channel, and gradient width curled channel, which is based on the thermal viscosity equivalent model and impedance equivalent model. Considering the over resistance effect caused by multi-unit composite structure, a multi-parameter control strategy was used to design bending acoustic metasurface (BAM) units for perfect sound absorption at four discrete frequencies of 546Hz, 563Hz, 585Hz, and 601Hz, which is based on the complex frequency plane method. and the thicknesses of these unites are only (1.2cm). The broadband and efficient sound absorption effect of the four parallel composite BAM units was theoretically studied. The simulation and experiment verified that the composite BAM not only achieved perfect sound absorption at 573Hz with a subwavelength thickness of 12mm, but also had an efficient sound absorption(α>0.8) frequency band of 512Hz-621Hz, with a bandwidth up to 109Hz. The research in this paper provides a certain theoretical basis for the design of low-frequency broadband compact acoustic structures, and has certain reference value for low-frequency broadband noise control.

Broadening efficient sound absorption bandwidth of spatial bending acoustic metasurfaces with multi-parameter variation

Zhang,

Chen,

Xiao

et al. 2024

Due to limitations in the space for the installation of noise reduction structures in some engineering application fields, broadband efficient noise reduction has always been a key issue in academic and engineering fields. Faced with this issue, in this work, a deep-subwavelength acoustic metasurface with embedded necks and bending channels is proposed. Firstly, theoretical models for the sound absorption coefficient of traditional Helmholtz resonators(THRs), embedded Helmholtz resonators(EHRs), and spatial bending acoustic metasurfaces (SBAMs) with a thickness of 12 mm were established using the thermal-viscous model, end acoustic radiation correction theory, and transfer matrix method, which prove that the SBAM unit has deep-subwavelength characteristics. Subsequently, adopting theoretical models and the complex frequency plane method, the SBAM unit with a side length of 50 mm and a thickness of 12 mm was designed, which exhibited perfect absorption at 541 Hz. The perfect absorption mechanism was elucidated through simulations. Theoretical and simulation models were used to analyze the regulation law of different geometric parameters on the acoustic performance for ultra-thin SBAM units. The results indicate that by accurately tuning multiple geometric parameters, ultrathin and perfect-absorption SBAM units with a thickness of 12 mm in the broadband range of 463–672 Hz can be achieved. Furthermore, it was experimentally studied how the equivalent length L influences the sound absorption performance of SBAM units, and the correctness of the theoretical and simulation results was verified. These results will provide a theoretical reference and engineering application for broadening the low-frequency noise reduction frequency band in compact spaces, improving the spatial utilization of sound absorption structures, and achieving broadband noise control at low and medium frequencies.