Page 27 - Summer 2006

acoustic diffusers over the last three decades. Alongside the designs outlined above, a sizeable literature has developed explaining how to measure, predict, and characterize the effects of surface diffusers. In the same way that absorption coefficients are specified, proof of performance standards have now been established that allow designers to specify coefficients relating to the amount of sound scattered and the quality or uniformity of the diffusion. Yet many questions still remain unanswered. Perhaps the most important ques- tion to answer is how much diffusion should be applied, and where diffusers should be used. While acoustic designers have produced many innovative new designs, the under- standing of where to apply diffusers lags behind and is still largely based on precedence. Maybe this is why eminent acousticians can still disagree on the role of diffusers within auditoria; or maybe it is just a case of individual taste.
Ultimately, whether a diffuser is used or not is a decision usually made by an architect who often has little or no acoustic training. The key to good diffuser design is to find forms that complement the architectural trends of the day. The diffuser must not only meet the acoustic specification, it must fit in with the visual scheme required by the architect. This means that diffuser design has moved away from its roots in number-theoretic reflection phase gratings. However, much of what has been learned from decades of work on Schroeder diffusers is still being applied today.AT
One answer to the Chinese remainder problem was 23.
1 M. R. Schroeder, “Diffuse sound reflection by maximum-length sequences,” J. Acoust. Soc. Am. 57(1), 149-150 (1975).
2 M. R. Schroeder, “Binaural dissimilarity and optimum ceilings for concert halls: more lateral sound diffusion,” J. Acoust. Soc. Am. 65, 958-963 (1979).
3 M. R. Schroeder, “Towards better acoustics for concert halls,” PhysicsToday 33(10), 24-30 (1980).
4 A. H. Marshall and J. R. Hyde, “Some practical considerations in the use of quadratic residue diffusing surfaces,” in Proceedings of the 10th Intl. Congress on Acoust., Sydney, paper E7.3 (1980).
5 A. H. Marshall, J. R. Hyde, and M. F. E. Barron, “The acoustical design of Wellington Town Hall: Design development, implemen- tation and modelling results,” In Proc. of the Institute of Acoustics (UK), Edinburgh, (Institute of Acoustics, UK, 1982).
6 M. Barron, “The subjective effects of first reflections in concert halls—the need for lateral reflections,” J. Sound Vib. 15, 475-94 (1971).
7 D. David and C. Davis, “The LEDE concept for the control of acoustic and psychoacoustic parameters in recording control rooms,” J. Audio Eng. Soc. 28, 585-595 (1980).
8 P. D’Antonio and J. Konnert, “The QRD diffractal: a new one- or two-dimensional fractal sound diffuser,” J. Audio. Eng. Soc. 40(3), 113-129 (1992).
9 J. A. S. Angus, “Using grating modulation to achieve wideband large area diffusers,” Applied Acoust. 60(2), 143-165 (2000).
10 T. J. Cox and P. D’Antonio, “Engineering art: The science of concert hall acoustics,” Interdiscip. Sci. Rev. 28(2), 119-129 (2003).
11 J. A. S. Angus, “Sound diffusers using reactive absorption grating,” 98th Convention of the Audio. Eng. Soc. preprint 3953 (1995).
12 P. Fan and M. Darnell, Sequence design for communications appli-
References
cations (John Wiley and Sons, NY, 1996).
13 D. Wells, The Penguin book of curious and interesting puzzles, Penguin Books, (1992).
14 T. J. Cox, J. A. S. Angus and P. D’Antonio, “Ternary and quadriphase sequence diffusers,” J. Acoust. Soc. Am. 119(1), 310-319 (2006).
Trevor Cox is a rec- ognized international expert in room acoustics and in 2004 was awarded the Tyndall medal by the Institute of Acoustics. He carries out research in performance room acoustics, investigating
how room conditions can be improved for good speech com- munication and quality music production and reproduction. Other research interests include signal processing, environ- mental noise and perception. Last year, Trevor was a finalist for FamelabTM, a UK competition to find the new face of science on television. He is currently working on a website to discover the worst sound in the world (www.sound101.org) and he has just been awarded a Senior Media Fellowship by the Engineering and Physical Sciences Council (UK).
Peter D’Antonio was born
in Brooklyn, NY, in 1941. He
received his B.S. degree from St.
John’s University in 1963 and his
Ph.D. from the Polytechnic
Institute of Brooklyn in 1967. In
1974 he developed the widely
used recording control room
design, utilizing a temporal
reflection free zone and reflec-
tion phase grating diffusors at
Underground Sound, Largo,
MD. Dr. D’Antonio is founder and president of RPG Diffusor Systems, Inc., established in 1983. He pioneered the sound dif- fusion industry and has significantly expanded the acoustical palette by creating and implementing a wide range of novel number-theoretic, fractal and optimized diffusing and absorb- ing surfaces, for which he holds many trademarks and patents. He has lectured extensively, published numerous scientific articles in technical journals and magazines and is the co- author of the reference book Acoustic Absorbers and Diffusers: Theory, Design and Application, Spon Press 2004. He served as Chairman of the Audio Engineering Society (AES) Subcommittee on Acoustic Working Group SC-04-02, which published AES-4id-2001; is a member of the ISO/TC 43/SC 2/WG25 Working Group, which published ISO standard 17497-1:2004; and has served as adjunct professor of acoustics at the Cleveland Institute of Music, since 1991. He is a Fellow of the Acoustical Society of America and the AES and a pro- fessional affiliate of the American Institute of Architects.
A Brief History of Room Acoustic Diffusers 25