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Improving the bass response of Schroeder diffusers

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Hargreaves, JA and Cox, TJ 2003, Improving the bass response of Schroeder diffusers , in: IOA Soundbite, November 2003, Oxford.

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    Abstract

    Room acoustic diffusers can be used to treat the acoustics of critical listening environments. A Schroeder diffuser is a popular type of diffuser which has the property of producing grating lobes of similar energy at most integer multiples of the design frequency. However at the critical frequencies, all the wells re-radiate in phase, so the diffuser appears to reflect sound like a flat surface. Space utilisation is also an issue for Schroeder diffusers, with a significant amount of the diffuser volume being unused. Folding the longest wells allows the diffuser to be packed into a smaller space, thereby making more efficient use of the space and allowing more bass diffusion. While well folding has been suggested before, it appears not to have been thoroughly investigated. A 2D Boundary Element Method is used to model the scattered energy from folded and normal versions of a Schroeder diffuser. This prediction model has been previously validated against measurement. At low frequency the diffuser with folded wells mimics the performance of a standard Schroeder diffuser. At high frequency there is an apparent change in the well depth sequence, which can be exploited to reduce the effects of critical frequencies.

    Item Type: Conference or Workshop Item (Lecture)
    Themes: Built and Human Environment
    Schools: Colleges and Schools > College of Science & Technology > School of Computing, Science and Engineering > Acoustics Research Centre
    Journal or Publication Title: Proceedings of the Institute of Acoustics
    Refereed: No
    Depositing User: JA Hargreaves
    Date Deposited: 16 Jan 2012 13:40
    Last Modified: 12 Apr 2012 10:58
    References: [1] P D’Antonio and T J Cox. Diffusor Application in Rooms. Applied Acoustics. 60(2). 113-142. June 2000. [2] M. R. Schroeder, “Diffuse sound reflection by maximum-length sequences,” J.Acoust.Soc.Am. 57(1), 149-150, (1975). [3] M. R. Schroeder, “Binaural dissimilarity and optimum ceilings for concert halls: more lateral sound diffusion”, J.Acoust.Soc.Am. 65, 958-963 (1979). [4] J. Hunecke, “Schallstreuung und schallabsorption von oberflchen aus mikroperforierten streifen,” University of Stuttgart, Ph.D. Thesis, (1997). [5] K. Fujiwara, K. Nakai and H. Torihara, "Visualisation of the sound field around a Schroeder diffuser," Applied Acoustics, 60(2), 225-236, (2000). [6] T. Wu, T. J. Cox, and Y. W. Lam, “A profiled structure with improved low frequency absorption,” J.Acoust.Soc.Am., 110, 3064-3070, (2001). [7] T. J. Cox and P. D’Antonio, “Acoustic Absorbers and Diffusers,” Spon Press, (2003 or 2004). [8] J. A. Angus, T. J. Cox, M. R. Avis and L. Xiao, “Sound diffusers using active impedance gratings,” Surface Acoustics 2003, proc. IoA 25(5), Salford (2003). [9] A. Jrvinen, L. Savioja and K. Melkas, “Numerical simulations of the modified Schroeder diffuser structure,” J.Acoust.Soc.Am., 103(5), 3065, (1998). [10] F. P. Mechel, "The wide-angle diffuser - A wide-angle absorber?” Acustica, 81, 379-401, (1995). [11] AES-4id-2001, “AES Information document for room acoustics and sound reinforcement systems – characterisation and measurement of surface scattering uniformity,” J.Audio Eng.Soc., 49(3), 149-165, (2001). [12] J. A. S. Angus and C. I. McManmon, "Orthogonal sequence modulated phase reflection gratings for wide-band diffusion," J.Audio Eng.Soc., 46(12), 1109-1118, (1998). [13] J. A. S. Angus, “Using grating modulation to achieve wideband large area diffusers,” Applied Acoustics, 60(2), 143-165, (2000). [14] T.J.Cox, J.A.S.Angus and P. D’Antonio, “The performance of Schroeder Diffusers: a wide band BEM investigation,” Surface Acoustics 2003, proc. IoA 25(5), Salford (2003). [15] T. J. Cox, “Optimization of profiled diffusers,” J.Acoust.Soc.Am., 97(5), 2928-2941, (1995).
    URI: http://usir.salford.ac.uk/id/eprint/19377

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