Broadband low-frequency noise control via Hexa-resonator array: Local resonances, coupling effect, and bandgap engineering

Environmental noise pollution (30-8000 Hz, 50-90 dB) has become a central health concern due to its impact on human psychology and physiology. Acoustically, aesthetic architecture has recently been explored for noise control, where sonic crystals (SCs) offer both effective sound attenuation and seamless architectural integration. However, conventional SCs with circular scatterers remain limited in suppressing low-frequency noise because Bragg scattering requires lattice constants comparable to the acoustic wavelength, making large structures impractical for subwavelength regimes. Herein, we propose a Hexa-resonator SC, optimized, simulated, and experimentally validated for its noise attenuation performance. With band structure calculations and eigenfrequency mode analysis, the insertion loss (IL) was investigated over 20-1000 Hz. In the sub-kilohertz region, the SC exhibited two first-order resonance peaks around 150 and 200 Hz and a first-order Bragg band (255-410 Hz). It showed a maximum IL of approximately 36 dB at 303 Hz (in the Bragg region), confirming its effectiveness for low-frequency noise attenuation. The influence of cavity geometry on phase pressure variations and IL was analyzed, revealing hybridization and mode coupling effects. Experiments qualitatively follow the simulated trends.