Diffusion of airborne sound using acoustic metamaterials

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Cheung, Fiona S.

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Acoustic surface treatments, such as absorbers and diffusers, are used to control unwanted reflections in rooms. These reflections, when excessive, can create an unpleasant experience for both audiences and performers in any space, not just performance spaces. Existing acoustic absorbers, including Helmholtz resonators, quarter-wave resonators, and panel absorbers, are discussed in this thesis. The most common diffuser, the Quadratic Residue Diffuser (QRD), is also explored in detail. While QRDs are well known for their predictability and ease of design, they suffer from two main drawbacks: size and aesthetics. This thesis explores the use of acoustic metamaterials, specifically coiled space metamaterials, to replace the QRD. These metamaterials seek to address these specific problems with QRD designs while replicating its ability to scatter acoustic waves in a predictable fashion. Two specific coiled space metamaterial designs are discussed in detail, and their responses are compared to that of the QRD to determine whether they can be viable replacements. The results of the comparisons, while unable to replicate the response of the standard QRD exactly, did show modest improvements. More validation must be done before a definitive answer can be given as to whether either of these designs are able to be successful replacements for the QRD


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