Objective Conventional sonic black holes (SBHs) exhibit excellent sound absorption primarily in medium- and high-frequency ranges but suffer from limited performance at frequencies below 200 Hz. Meanwhile, individual Helmholtz resonators generally provide narrow effective absorption bandwidths. Existing hybrid sound absorbers have yet to simultaneously achieve enhanced low-frequency absorption, broadband characteristics, and structural reconfigurability, which limits their application in differentiated low-frequency noise control for ship cabins.
Method A reconfigurable parallel sound absorber integrating sonic black holes with extended-neck Helmholtz resonators (SBH-HREN) is proposed. The transfer matrix method and equivalent medium theory are employed to establish an acoustic model of the parallel composite structure, and thermoviscous finite element simulations are conducted using COMSOL for numerical validation. Parametric studies are performed to investigate the effects of neck length, tube diameter, cavity depth and loss factor on the sound absorption spectra. Standard impedance tube experiments are carried out using fabricated prototypes, and the absorption curves obtained from theoretical predictions, numerical simulations, and experimental measurements are comprehensively compared. Complex frequency plane analysis and internal sound pressure distributions are employed to elucidate the coupled absorption mechanisms. The modular detachable design enables independent replacement of resonator units, allowing the absorber to adapt to varying noise spectra.
Results Under normal-incidence plane-wave excitation, the average sound absorption coefficient of standalone SBHs is only 0.21. The proposed SBH-HREN achieves an absorption coefficient of 0.8 within the 150–200 Hz frequency range, which is nearly four times that of standalone SBHs. Moreover, the average sound absorption coefficient remains at 0.82 over the range of 400–1600 Hz. The low-frequency absorption peak can be continuously tuned by adjusting the geometric parameters of the resonator units, and the theoretical predictions, numerical simulations, and experimental measurements exhibit consistent variation trends.
Conclusion The parallel modular structure integrates the low-frequency resonant absorption of Helmholtz resonators with the broadband energy dissipation capability of sonic black holes, resulting in significantly enhanced low-frequency sound absorption. Replaceable resonator units enable spectral reconfiguration, while the compact design makes the absorber suitable for space-constrained ship cabins. This study provides a lightweight acoustic metamaterial solution for low-frequency air-borne noise suppression in marine vessels.
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