Maximum length sequence and Bessel diffusers using active technologies

Cox, TJ; Avis, MR; Xiao, L

Abstract

Active technologies can enable room acoustic diffusers to operate over a wider bandwidth than passive devices, by extending the bass response. Active impedance control can be used to generate surface impedance distributions which cause wavefront dispersion, as opposed to the more normal absorptive or pressure-cancelling target functions. This paper details the development of two new types of active diffusers which are difficult, if not impossible, to make as passive wide-band structures. The first type is a maximum length sequence diffuser where the well depths are designed to be frequency dependent to avoid the critical frequencies present in the passive device, and so achieve performance over a finite-bandwidth. The second is a Bessel diffuser, which exploits concepts developed for transducer arrays to form a hybrid absorber–diffuser. Details of the designs are given, and measurements of scattering and impedance used to show that the active diffusers are operating correctly over a bandwidth of about 100 Hz to 1.1 kHz. Boundary element method simulation is used to show how more application-realistic arrays of these devices would behave.

Citation

Cox, T., Avis, M., & Xiao, L. (2006). Maximum length sequence and Bessel diffusers using active technologies. Journal of Sound and Vibration, 289(4-5), 807-829. https://doi.org/10.1016/j.jsv.2005.02.019

• Journal Article Type: Article
• Publication Date: Feb 7, 2006
• Deposit Date: Sep 10, 2007
• Publicly Available Date: Apr 5, 2016
• Journal: Journal of Sound and Vibration
• Print ISSN: 0022-460X
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 289
• Issue: 4-5
• Pages: 807-829
• DOI: https://doi.org/10.1016/j.jsv.2005.02.019