Spectrally smooth and spatially uniform sound radiation from a thin plate structure using band gaps

Abstract

As an alternative to conventional loudspeakers, panel loudspeakers have been investigated. However, it is challenging to avoid structural modes in a panel loudspeaker, which results in an uneven frequency spectrum and highly directional sound radiation. Here, we present a technique to eliminate modes in a frequency range of interest based on a band gap (BG) structure that forbids the propagation of waves. In order to open a BG between 300 and 500 Hz, a thin aluminum plate with periodic resonators is considered. Using finite element (FE) simulations, vibro-acoustic responses of the BG structure are analyzed, leading to more spectrally smooth and spatially uniform sound radiation. Experimental results agree well with the numerical predictions, displaying a smoother frequency spectrum and smaller variation of sound pressure at six different measurement orientations in an anechoic chamber. For this specific case, the overall SPL is amplified by 5.5 dB and the standard deviation is reduced by 5.7 dB at frequencies ranging from 300 Hz to 500 Hz.