Noise reduction study based on embedded spiral neck Helmholtz resonators

Due to the long wavelengths of low-frequency sound waves, conventional sound-insulating materials are physically limited and cannot effectively attenuate their propagation. We design metamaterials based on Helmholtz resonators combined with a space-coiling strategy, which feature the annular arrangement of resonant units with embedded spiral necks around a central waveguide channel, enabling noise suppression while maintaining air ventilation. The sound insulation performance of materials was evaluated by measuring and numerically simulating the transmission loss using an impedance tube. The results demonstrate that increasing the pitch raises the resonance frequency and broadens the sound insulation bandwidth. Stacking multiple layers significantly improves transmission loss and expands the operational bandwidth. Moreover, utilizing hybrid-pitch designs within or across layers induces multiple resonance peaks, broadening the sound insulation band via peak blending. By optimizing the unit arrangement with a higher ventilation area ratio, the structure maintains satisfactory sound attenuation in the low-frequency band. The structure can achieve effective low-frequency noise suppression below 500 Hz while maintaining ventilation performance.