This study presents an acoustic membrane design utilizing a thin foil sound resonance mechanism to enhance sound absorption and insulation performance. The membranes incorporate single-layer and double-layer structures featuring parallel foil square wedge-shaped coffers and a flat bottom panel, separated by air cavities. The enclosed air cavity significantly improves the sound insulation capability of the acoustic membrane. Parametric studies were conducted to investigate key factors affecting the sound transmission loss (STL) of the proposed acoustic membrane. The analysis examined the influence of foil thickness, substrate thickness, and back cavity depth on acoustic performance. Results demonstrate that the membrane structure enriches vibration modes in the 500–6000 Hz frequency range, exhibiting multiple acoustic attenuation peaks and broader noise reduction bandwidth (average STL of 40–55 dB across the researched frequency range) compared to conventional resonant cavities and membrane-type acoustic metamaterials. The STL characteristics can be tuned across different frequency bands by adjusting the back cavity depth, foil thickness, and substrate thickness. Experimental validation was performed through noise reduction tests on an air compressor pump. Comparative acoustic measurements confirmed the superior noise attenuation performance and practical applicability of the proposed membrane over conventional acoustic treatments. Compared to uniform foil resonators, the combination of plastic and steel materials with single-layer and double-layer membranes reduced the overall sound level (OA) by an additional 2–3 dB, thereby offering exceptional STL performance in the low- to medium-frequency range. These lightweight, easy-to-manufacture membranes exhibit considerable potential for noise control applications in household appliances and industrial settings.

Acoustic metasurfaces have paved the way for the ongoing development of compact sound-absorbing devices that possess excellent ventilation capabilities. However, existing absorption mechanisms primarily focus on plane-wave fronts while neglecting omnidirectionally radiated cylindrical waves. In this study, drawing inspiration from wave-interference theory, we propose an approach to absorb cylindrical sound waves by combining artificially decorated passive monopoles and dipoles, which are synthesized by a coiled space resonator and a double-channel resonator, respectively. To demonstrate the effectiveness of our approach, we construct an ultrasparse annular metasurface absorber with an air-channel-area ratio of 46% and a deep-subwavelength thickness. Remarkably, this absorber achieves an absorption performance of 96% (91% in the experiment) for omnidirectionally radiated cylindrical sound waves. This achievement is realized by utilizing a circular array composed of 36 metamolecules arranged in a ringlike grating structure, with each metamolecule supporting synthesized multipoles. The near-unity absorption is accomplished through destructive interference between the composite monopole and dipole, characterized using a one-dimensional impedance tube. This high-efficiency absorption, combined with excellent ventilation and compactness, introduces alternative possibilities for designing functional sound-absorbing devices that can handle low-frequency sound waves with complex wave fronts.

The rapid development of acoustic metamaterials has opened new possibilities for creating perfect absorbers; however, achieving compact devices for extremely low-frequency sound remains a challenge. In this work, we present a proposal for the development of extremely low-frequency sound absorbers through coupling dissipated meta-atoms to an impedance boundary (IB). The IB is engineered by a dual-port opening MPP–cavity–MPP sandwich structure, exhibiting sound impedance significantly lower than that of a rigid wall, as well as considerable sound absorption across the entire audible spectrum. To further enhance absorption, a hybridized system integrating over-damped resonators with the IB is proposed, giving rise to a composite impedance boundary resonator absorber. Conceptually, we have theoretically and experimentally demonstrated an ultralow-frequency absorber, which achieves average absorptance of 82% within the frequency ranges of 50–150 Hz. The total structural thickness is only 176 mm, which corresponds to 1/39 of the wavelength at 50 Hz. Our strategy leverages the synergistic effect between the IB and over-damped meta-atoms, which may enable efficient broadband absorption at extremely low frequencies.