Volume 127, Issue 1, January 2010
Index of content:
- ARCHITECTURAL ACOUSTICS 
Optimum absorption and aperture parameters for realistic coupled volume spaces determined from computational analysis and subjective testing results127(2010); http://dx.doi.org/10.1121/1.3268604View Description Hide Description
This project utilizes computational modeling to study the effects of varying two architectural parameters, absorption ratio and aperture size, in a realistic coupled volume concert hall. Coupled volumes have been shown to exhibit non-exponential sound energy decay profiles, referred to as double slope effect. A number of objective metrics (T30/T15, LDT/T10, decay ratio, and ) have been used to quantify the double slope effect of the profiles generated in the virtual hall. T30/T15 and LDT/T10 showed similar trends across all hall configurations, indicating decreasing double slope effect with increasing coupled volume absorption ratio for each aperture size, and producing highest values at a specific aperture size for each absorption ratio. Generally, LDT/T10 provides finer resolution than T30/T15 when analyzing the decay profiles in this study. Results from the two metrics derived from Bayesiananalysis, decay ratio and , seem less consistent. Subjective testing has also been conducted to determine the effect of varying the two architectural parameters in the hall, and multidimensional scalinganalysis shows that, in general, listener preference is inversely proportional to the level of double slope effect, with the highest levels of preference occurring at low and medium levels of double slope effect. Recommended design guidelines for coupled volume halls are provided based on these computational and subjective results.
127(2010); http://dx.doi.org/10.1121/1.3271034View Description Hide Description
Reverberation rooms are often used for measuring the sound power emitted by sources of sound. At medium and high frequencies, where the modal overlap is high, a fairly simple model based on sums of waves from random directions having random phase relations gives good predictions of the ensemble statistics of measurements in such rooms. Below the Schroeder frequency, the relative variance is much larger, particularly if the source emits a pure-tone. The established theory for this frequency range is based on ensemble statistics of modal sums and requires knowledge of mode shapes and the distribution of modal frequencies. This paper extends the far simpler random wavetheory to low frequencies. The two theories are compared, and their predictions are found to compare well with experimental and numerical results.
127(2010); http://dx.doi.org/10.1121/1.3257590View Description Hide Description
In the pursuit of more effective noise control devices, the cavity backed micro-perforated panel absorber (CBMPPA) is developed in this study. A CBMPPA differs from the conventional micro-perforated panel (MPP) absorber in that the MPP is backed by a trapezoidal cavity, which allows more effective vibroacoustic coupling between the MPP and the cavity. A two-dimensional theoretical model is established and tested both numerically and experimentally. Based on the verified theoretical model,sound absorption performance of a trapezoidal CBMPPA is investigated numerically. Results show that the shape of the backing cavity can significantly alter the sound absorption mechanisms and frequency distribution of overall sound absorption coefficient of the absorber. Further analyses show that acoustic modes that are initially decoupled from the MPP in the rectangular configuration are coupled with the air motion in the MPP, which accounts for the change in absorption pattern of the trapezoidal CBMPPA. By the same token, it also provides the flexibility for tuning the effective absorption range of the absorber. Due to the varying impedance matching conditions, the absorption performance of the trapezoidal CBMPPA exhibits obvious local characteristics over the MPP surface, which contrasts with the spatially uniform absorption in the conventional MPP absorber.
127(2010); http://dx.doi.org/10.1121/1.3263611View Description Hide Description
The existing body of literature regarding the acoustic design of concert halls has focused almost exclusively on classical music, although there are many more performances of popular music, including rock and pop. Objective measurements were made of the acoustics of 20 rock music venues in Denmark and a questionnaire was used in a subjective assessment of those venues with professional rock musicians and soundengineers as expert listeners. Correlations between the measurements show that clarity, including bass frequencies down to , is important for the general impression of the acoustics of the hall. The best-rated halls in the study have reverberation times that are approximately frequency independent from for hall volumes from . The worst rated halls in the study had significantly higher reverberation times in the 63 and bands. Since most audiences at rock concerts are standing, absorption coefficients were measured with a standing audience from . These measurements showed that a standing audience absorbs about five times as much energy in mid-/high-frequency bands as in low-frequency bands.