TUESDAY MORNING, 6 MAY 2014 555 A/B, 8:15 A.M. TO 11:55 A.M. Session 2aAA Architectural Acoustics: Uncertainty in Describing Room Acoustics Properties I Lily M. Wang, Cochair Durham School of Architectural Eng. and Construction, Univ. of Nebraska-Lincoln, 1110 S. 67th St., Omaha, NE 68182-0816 Ingo B. Witew, Cochair Inst. of Techn. Acoust., RWTH Aachen Univ., Neustrasse 50, Aachen 52066, Germany Chair’s Introduction—8:15 Invited Papers 2a TUE. AM 8:20 2aAA1. Review of the role of uncertainties in room acoustics. Ralph T. Muehleisen (Decision and Information Sci., Argonne National Lab., 9700 S. Cass Ave., Bldg. 221, Lemont, IL 60439, [email protected]) While many aspects of room acoustics such as material characterization, acoustic propagation and room interaction, and perception have long been, and continue to be, active areas of room acoustics research, the study of uncertainty in room acoustics has been very limited. Uncertainty pervades the room acoustic problem: there is uncertainty in measurement and characterization of materials, uncer- tainty in the models used for propagation and room interaction, uncertainty in the measurement of sound within rooms, and uncertainty in perception. Only recently are the standard methods of uncertainty assessment being systematically employed within room acoustics. This paper explains the need for systematic study of uncertainty in room acoustic predictions and review some of the most recent research related to characterizing uncertainty in room acoustics. 8:40 2aAA2. Uncertainty and stochastic computations in outdoor sound propagation. D. Keith Wilson (CRREL, U.S. Army ERDC, 72 Lyme Rd., Hanover, NH 03755-1290, [email protected]) and Chirs L. Pettit (Aerosp. Eng., U.S. Naval Acad., Annapolis, MD) Outdoor sound propagation provides an interesting and informative example of uncertainty in acoustics. Predictions are strongly impacted by imperfect knowledge of the atmospheric and ground properties, as well as by random turbulence and unresolved elements of the landscape. This presentation describes the impact of such uncertainties and how they can be quantified with stochastic sampling techniques that are applicable to a wide variety of acoustical problems. Efficient and accurate computational approaches result from simultaneously sampling over frequency, uncertain environmental properties, and random processes. Among the techniques considered are ordinary Monte Carlo and Latin hypercube sampling, importance sampling based on relatively simpler propagation models, and adaptive importance sampling. When uncertainties in the atmospheric and ground properties dominate, importance sampling is found to converge to an accurate estimate with the lowest calculation time. When random turbulent scattering dominates, the sampling method has little impact. 9:00 2aAA3. Bias and reproducibility of sound power test methods. Matthew G. Blevins, Lily M. Wang, and Siu-Kit Lau (Durham School of Architectural Eng. and Construction, Univ. of Nebraska-Lincoln, 909 S 70th plz #4, Omaha, NE 68106, [email protected]) Sound power is a useful quantity in describing the strength of an acoustic source because its value is independent of distance. How- ever, many standardized methods exist for the measurement of sound power and comparison between methods can give rise to discrep- ancies. An interlaboratory study was designed according to the ISO 5725 series to quantify the bias and reproducibility of three common sound power measurement methods in the HVACR industry: free field method, diffuse field method, and sound intensity method. A loudspeaker sound source was used to generate two test signals: a broadband signal with decreasing 5 dB slope per octave band, and the same broadband signal with discrete frequency tones at 58, 120, 300, and 600 Hz. The objective of the study is to quantify repeatability, reproducibility, laboratory bias, and measurement method bias, as well as investigate the influence of tones. The design of the interlabor- atory study and preliminary results will be presented. The ISO 5725 methods used to investigate the sound power measurement methods in this study may be applicable to other room acoustic measurements. 2203 J. Acoust. Soc. Am., Vol. 135, No. 4, Pt. 2, April 2014 167th Meeting: Acoustical Society of America 2203 9:20 2aAA4. Uncertainty aspects regarding the input for reverberation time predictions. Margriet Lautenbach (Peutz bv, PO Box 696, Zoetermeer 2700 AR, Netherlands, [email protected]) and Martijn Vercammen (Peutz bv, Mook, Netherlands) The outcome of a reverberation time prediction cannot be more accurate than the combined accuracy of input parameters. In the cur- rent procedures of measuring absorption coefficients and using them in prediction models at least two aspects regarding the accuracy of absorption coefficients are quite underexposed:(1) The precision of the measurement: the reproducibility both within one laboratory as between different laboratories or laboratory conditions; (2) The accuracy of the measurement: the dependency of the absorption coeffi- cient on the measurement procedure in general. The upcoming ISO 354 improves both aspects by means of a more elaborate qualifica- tion procedure, the use of a reference absorber combined with a correction procedure, as well as a guidance for the extrapolation of the results to other dimensions. Still, it is interesting to think about the impact of the remaining accuracy. To what extend is an acoustic con- sultant “at risk” using absorption coefficients, apart from using correct modeling algorithms. Two different, but common cases, can give an idea of the influence of the accuracy, two situations in which the reverberation time heavily depends on one absorption material: a class room with an absorptive ceiling, and a concert hall with absorptive chairs. 9:40 2aAA5. Investigations into the sound absorbing properties of gypsum wall board. Robert Healey (Architectural Eng., Univ. of Kansas, 1241 Tennessee Apt. 3, Lawrence, KS 66044, [email protected]), Kevin Butler (Henderson Engineers, Inc., Lawrence, KS), Ian Patrick, and Sean Quigley (Architectural Eng., Univ. of Kansas, Lawrence, KS) Gypsum wall board is one of the most common materials encountered in buildings and thus encountered in architectural acoustics. Recent research into gypsum wall board sound absorption has indicated that the material may have significantly less absorption than is usually assumed when employed in certain construction assemblies. This paper examines both traditional mountings and a new method for determining sound absorption recently introduced involving mounting a gypsum board assembly in an opening between two rever- berant rooms commonly used for transmission loss testing. Sound absorbing data were obtained with the two-room method along with the traditional measurement method, for several gypsum wall board wall assemblies, and with an attempt to compare the measured results to real world experience. 10:00–10:15 Break 10:15 2aAA6. The effects of uncertain scattering coefficients on the reverberation time. Uwe M. Stephenson (Room Acoust., HafenCity Univ. Hamburg, Nelkenweg 10, Bad Oldesloe 23843, Germany, [email protected]) and Alexander Pohl (Room Acoust., HafenCity Univ. Hamburg, Hamburg, Germany) Uncertain scattering coefficients are still a weak point in room acoustical computer simulations and predictions. The definition of the scattering coefficient s, their values as well as the simulation model are uncertain. Not only the roughness of infinite walls but also the edge effect are included in a combined diffusivity coefficient ray tracing models utilize. Most interesting in practical room acoustics is the influence on the uncertainty of the reverberation time (RT), which depends very sensitively on s. However, there is no analytical for- mula for the RT for only partially diffusely reflecting surfaces. In non-diffuse sound fields, the RT depend on the room shape, the distri- bution of absorption and especially on the scattering coefficients, too. A crucial example is a long rectangular room with totally absorbing side walls and partially scattering front walls. For this case a semi-analytical approach had been found. These and other typical cases in 2D and 3D have now been investigated numerically by the Sound Particle Simulation Method (SPSM) and the Anisotropic Reverberation Model (ARM). The aim is to find semi-analytically formulae or rules to estimate the uncertainty in the prediction of the RT by the Sabine formula. Is an “equivalent scattering area” a useful concept? 10:35 2aAA7. Uncertainty in scattering coefficient measurements of sintered ceramic tiled surfaces. David T. Bradley (Phys. þ Astron- omy, Vassar College, 124 Raymond Ave., #745, Poughkeepsie, NY 12604, [email protected]), Rhett Russo (School of Architec- ture, New Jersey Inst. of Technol., Newark, NJ), Ariana Sharma, and Jacob Adelgren (Phys. þ Astronomy, Vassar College, Poughkeepsie, NY) The reflection of acoustic energy in an enclosed space can sometimes lead to undesirable effects, particularly if the reflection is rela- tively large in amplitude or delayed in time. To mitigate these effects, surfaces with non-planar geometries, which are known as diffus- ers, can be employed in an architectural space to improve the acoustical qualities of the space by attenuating these harsh reflections and by producing a more evenly distributed sound field. One of the standardized quantifiers used to characterize the effectiveness of a dif- fuser is the scattering coefficient,