Meta-silencer with designable timbre

Timbre, as one of the essential elements of sound, plays an important role in determining sound properties, whereas its manipulation has been remaining challenging for passive mechanical systems due to the intrinsic dispersion nature of resonances. Here, we present a meta-silencer supporting intensive mode density as well as highly tunable intrinsic loss and offering a fresh pathway for designable timbre in broadband. Strong global coupling is induced by intensive mode density and delicately modulated with the guidance of the theoretical model, which efficiently suppresses the resonance dispersion and provides desirable frequency-selective wave-manipulation capacity for timbre tuning. As proof-of-concept demonstrations for our design concepts, we propose three meta-silencers with the designing targets of high-efficiency broadband sound attenuation, efficiency-controlled sound attenuation and designable timbre, respectively. The proposed meta-silencers all operate in a broadband frequency range from 500 to 3200 Hz and feature deep-subwavelength sizes around 50 mm. Our work opens up a fundamental avenue to manipulate the timbre with passive resonances-controlled acoustic metamaterials and may inspire the development of novel multifunctional devices in noise-control engineering, impedance engineering, and architectural acoustics.