Thin curved acoustic metamaterial enclosure for low-frequency broadband noise reduction

Achieving efficient noise isolation for small-to-medium-sized noise sources through thin, lightweight, and compact structures is an effective strategy for controlling electromechanical product noise. To simultaneously address the poor sound-leakage resistance of conventional reflection-type enclosures and the weak low-frequency isolation of thin porous materials, this paper proposes a curved acoustic metamaterial enclosure composed of thin sound-absorbing metamaterials and thin porous materials. The thin sound-absorbing metamaterials are based on an in-plane space-coiling design concept that shifts the thickness-dimensional space required by the sound-absorbing structure into a planar thin layer, effectively reducing the enclosure wall thickness. Furthermore, a parallel arrangement of multiple metamaterial modules with differentiated operating frequency bands effectively broadens the noise reduction bandwidth. Since the proposed acoustic metamaterial enclosure is primarily composed of sound-absorbing structures, it can effectively dissipate sound energy, thus mitigating the sound-leakage problem inherent to conventional reflection-type enclosures. The designed acoustic metamaterial enclosure has a height of 410 mm, an inner diameter of approximately 337 mm and a wall thickness of 23 mm. Experimental results from laboratory tests in a reverberation room demonstrate that the acoustic metamaterial enclosure exhibits favorable noise reduction performance in the 200–5000 Hz range. Under comparable external installation space constraints, the acoustic metamaterial enclosure achieves a 6.1 dB improvement in noise reduction performance compared with the conventional reflection-type leather enclosure, simultaneously achieving a low profile and high-efficiency noise reduction. Additionally, it benefits from structural simplicity, adaptability to curved surfaces, and high space efficiency, showing considerable promise for noise control in space-constrained electromechanical equipment.