Low-frequency noise remains difficult to control in built environments, particularly where ventilation must be maintained and conventional mass-law barriers are ineffective. This keynote presents a full-scale ventilated metacage that combines plate-type and Helmholtz-type acoustic metamaterials in a modular 3D-printed architecture for tunable low-frequency noise control. Finite element simulations and laboratory validation in both anechoic and reverberant environments show that the hybrid design achieves broadband attenuation from 80 Hz to 320 Hz, with a peak insertion loss of 16 dBA at 160 Hz. Parametric optimization and airflow measurements demonstrate that the coupled resonant responses of the two metamaterial types extend the effective attenuation bandwidth while preserving natural ventilation. A shaker-noise case study further confirms angle-independent insertion-loss trends and reveals the influence of flanking paths on performance. Beyond the full-scale prototype, the metacage concept is extended to polygonal configurations, including one-dimensional and two-dimensional metabarriers based on cuboctahedral units assembled from plate-type metamaterials. Their self-stacking geometry simplifies assembly, while their reconfigurability enables adjustment of interior cavity volume to tune insertion-loss characteristics. Together, these results bridge the gap between laboratory metamaterials and practical, scalable noise-control solutions for interior building applications.

Heow Pueh LEE is currently a Professor at the Department of Mechanical Engineering, National University of Singapore. He graduated with first class honours from Cambridge University and PhD in Mechanical Engineering from Stanford University. His more recent works focus on acoustics and vibration, metamaterials, and composite structures. He is a Deputy Editor-in-Chief for Applied Acoustics, and member of Editorial Board for the International Journal of Applied Mechanics, Acta Mechanical Sinica, and Scientific Reports. He has more than 500 journal publications with google scholar H index of 81 and citations of more than 28,000.