An extra-broadband compact sound-absorbing structure composing of double-layer resonator with multiple perforations.

Abstract

Based on multi-layer Helmholtz resonators with extended necks (HREN), a compact sound-absorbing structure is developed for extra-broadband sound absorption. The structure of HREN with a single perforation is beneficial for low-frequency absorption under a thin thickness. However, it faces the problem of effectively attenuating noise only within a narrow frequency bandwidth near the resonance frequency. To widen its effective absorption bandwidth, two potential solutions are proposed and evaluated: (1) increasing the perforation number, and (2) adding extra layers in series. Results reveal that more perforations produce a wider half-absorption bandwidth, and the added layers induce more absorption peaks. Thus, a multi-layer HREN unit with multiple perforations is a favorable candidate for broadband sound absorption. On the basis of these, we design a broadband acoustic structure constructed by 11 coupled parallelly arranged double-layer HREN units with multiple perforations. The structure possesses an average sound-absorption coefficient of 0.9 in a prescribed frequency ranging from 800 to 3000 Hz. The absorption effectiveness of the structure is validated via experiments. What is more, the dimension of the absorber is only 50 mm (long)×50 mm (width)×41 mm (depth), indicating its compact characteristic. Hence, the developed extra broadband and compact sound-absorbing structure possesses a promising potential in various engineering applications.