Ternary and quadriphase sequence diffusers

Angus, JAS; Cox, TJ; D'Antonio, P

Abstract

A room acoustic diffuser breaks up reflected wavefronts, and this can be achieved by presenting a spatially varying surface impedance. In hybrid surfaces, varying impedance is achieved by patches of absorption and reflection, giving reflection coefficients nominally of 0 and 1. These surfaces are hybrids, absorbing some of the incident sound while diffusing any reflected energy. A problem with planar hybrid surfaces is that specular energy is only removed by absorption. By exploiting interference, by reflecting waves out-of-phase with the specular energy, it is possible to diminish the specular energy further. This can be achieved by using a diffuser based on a ternary sequence that nominally has reflection coefficients of 0, -1, and +1. Ternary sequences are therefore a way of forming hybrid absorber-diffusers that achieve better scattering performance without additional absorption. This paper discusses methods for making ternary sequence diffusers, including giving sequence generation methods. It presents prediction results based on Fourier and boundary element method models to examine the performance. While ternary diffusers have better performance than unipolar binary diffusers at most frequencies, there are frequencies at which the performances are the same. This can be overcome by forming diffusers from four-level, quadriphase sequences.

Citation

Angus, J., Cox, T., & D'Antonio, P. (2006). Ternary and quadriphase sequence diffusers. ˜The œJournal of the Acoustical Society of America (Online), 119(1), 310-319. https://doi.org/10.1121/1.2139632

• Journal Article Type: Article
• Publication Date: Jan 1, 2006
• Deposit Date: Sep 10, 2007
• Publicly Available Date: Apr 5, 2016
• Journal: The Journal of the Acoustical Society of America (JASA)
• Print ISSN: 0001-4966
• Peer Reviewed: Peer Reviewed
• Volume: 119
• Issue: 1
• Pages: 310-319
• DOI: https://doi.org/10.1121/1.2139632
• Publisher URL: http://asadl.org/jasa/resource/1/jasman/v119/i1/p310_s1
• Additional Information: Access Information : Copyright (2006) Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America.