Spherical metacage for low-frequency noise reduction

Low-frequency noise attenuation is crucial for effective noise control, and this study presents an innovative spherical metacage designed for this purpose. The metacage is composed of membrane plate-type components with inclined edges, creating a structure fully covered by lightweight, efficient acoustical metamaterials specifically targeting low-frequency noise. Aesthetic appeal is enhanced by the use of colored PVC sheets in the design. Through experimentally validated scaled numerical simulations, the study confirms the metacage's ability to mitigate low-frequency noise via the resonance of coupled Helmholtz resonator cavities formed by elastic membranes. The spherical configuration optimizes sonic enclosure to maximize sound insulation. The design achieves dual-peak sound insulation and establishes a wide bandgap below 1000 Hz, marked by high insertion loss. Additionally, the substitution of five membrane components with adjustable, ventilated Helmholtz resonator components preserves an effective bandgap across two different frequency regions. These ventilated components attenuate noise by utilizing the resonance of side cavities, where the passage of sound waves disrupts small air masses at the orifices. This arrangement expands the effective frequency range while minimizing the amplification effects of internal cavity resonance. The proposed reconfigured structure thus provides a promising solution for low-frequency noise attenuation, while also meeting ventilation requirements.