Volume 122, Issue 5, November 2007
Index of content:
- ARCHITECTURAL ACOUSTICS 
122(2007); http://dx.doi.org/10.1121/1.2783126View Description Hide Description
A method is presented to determine the bulk elastic properties of isotropic elastic closed-cell foams from impedance tube sound absorption tests. For such foams, a resonantsound absorption is generally observed, where acoustic energy is transformed into mechanical vibration, which in turn is dissipated into heat due to structural damping. This article shows how the bulk Young’s modulus, Poisson’s ratio, and damping loss factor can be deduced from the resonantabsorption. Also, an optimal damping loss factor yielding 100% of absorption at the first resonance is defined from the developed theory. The method is introduced for a sliding edge condition which is an ideal condition. Then, the method is extended to a bonded edge condition which is more easily achievable and additionally enables the identification of the Poisson’s ratio. The method is experimentally tested on expanding closed-cell foams to find their elastic properties in both cases. Using the found properties,sound absorption predictions using an equivalent solid model with and without surfaceabsorption are compared to measurements. Good correlations are obtained when considering surfaceabsorption.
High-resolution plane-wave decomposition in an auditorium using a dual-radius scanning spherical microphone array122(2007); http://dx.doi.org/10.1121/1.2783204View Description Hide Description
The spatial and temporal distribution of early reflections in an auditorium is considered important for sound perception. Previous studies presented measurement and analysis methods based on spherical microphone arrays and plane-wave decomposition that could provide information on the direction and time of arrival of early reflections. This paper presents recent results of room acoustics analysis based on a spherical microphone array, which employs high spherical harmonics order for improved spatial resolution, and a dual-radius spherical measurement array to avoid ill-conditioning at the null frequencies of the spherical Bessel function. Spatial-temporal analysis is performed to produce directional impulse responses, while analysis based on the windowed Fourier transform is employed to detect direction of arrival of individual reflections at selected frequencies. Experimental results of sound-fieldanalysis in a real auditorium are also presented.