Synergistic acoustic metamaterial for soundproofing: Combining membrane and locally resonant structure

Low-frequency and broadband noise reductions have always been a major industrial concern, as they pose a significant challenge. Although acoustic metamaterials are garnering attention in this field, they cannot simul-taneously block low-frequency and broadband noise. Thus, this study developed a synergetic soundproofing acoustic metamaterial (SSAM) comprising a membrane and locally resonant structure (LRS) to realize low -frequency and broadband sound insulation. The SSAM suppresses structure-borne noise by utilizing LRS-induced anti-resonance for low-frequency sound insulation and membrane-induced anti-resonance for broad-band sound insulation. The soundproofing mechanism of the proposed design was clarified through the dynamic effective density estimated using two impedance models (apparent and transfer impedances), and its sound insulation performance was validated through sound transmission loss simulations. The experimental sound pressure level results indicate that plate-and enclosure-type SSAMs can provide excellent low-frequency and broadband sound insulation. In the future, SSAMs will serve as a reference for the development of materials with noise-reduction capabilities for soundproofing applications, such as home appliances, vehicles, machinery products, and acoustic walls.