Sound Insulation Experimentation of Acoustic Metamaterial Partitions Under Diffuse Field Conditions

Abstract

Insulation systems based on mechanical metamaterials can considerably increase acoustic insulation performance in targeted frequency regions. The ability of metamaterials to attenuate waves with much larger wavelengths than the metamaterial dimensions offers a key advantage compared with conventional material approaches which normally require both a high mass and a large footprint. However, theoretical studies and experiments on the transmission loss of metamaterial-based systems, have almost invariably been limited to normal incidence sound whereas, in use, building partitions will be subject to diffuse field conditions. We designed several locally resonant structures (LRS), to provide transmission bandgaps in frequency regions where lightweight double leaf partitions normally exhibit poor insulation and tested them under reverberant conditions. Large improvements (over 10 dB) in the sound reduction index were obtained compared with conventional partitions of comparable weight. The results showed good agreement with modelling predictions. These experiments demonstrate that mechanical metamaterials can be scaled up to suit applications in buildings, but also show significant differences from normal incidence results and highlight some of the additional complications involved.

Keywords: Metamaterials, Broadband vibration insulation, Diffuse field