Volume 125, Issue 1, January 2009
Index of content:
- GENERAL LINEAR ACOUSTICS 
Sound transmission loss of rectangular and slit-shaped apertures: Experimental results and correlation with a modal model125(2009); http://dx.doi.org/10.1121/1.3003084View Description Hide Description
Among noise control techniques, enclosures are widely used. It is known that enclosure acoustic efficiency is strongly influenced by the presence of openings or leaks. Modeling of diffuse field sound transmission loss (TL) of apertures and slits is therefore critical when the enclosure acoustic performance characteristics need to be predicted with confidence either for design or for modifying existing enclosures. Recently, a general model for diffuse field sound TL of rectangular and circular apertures has been developed and validated with respect to existing analytical or numerical models. This paper presents an experimental validation of this new model. The aim was to develop a simple, reliable tool for predicting enclosure insertion loss using statistical energy analysis. Twelve out of the 15 test configurations were found to be reliable and were compared with theoretical models, which in fact correlate closely (without adjustment) with the experimental work.
125(2009); http://dx.doi.org/10.1121/1.3035839View Description Hide Description
Some further refinements are described for the -matrix approach to acoustic scattering. From the structure of the matrices involved, one can infer the Rayleigh limit explicitly for objects having no density contrast. One finds , where the -matrix involves integrals of the regular spherical wave functions over the object’s surface. The index of refraction and loss factor can be chosen as desired, and energy balance and reciprocity requirements are found to be met. The derivation can be extended to obtain the Rayleigh expansion, effectively describing as a series in ascending powers of the ratio of object size to wavelength. In trial cases, the series converges throughout the Rayleigh region and somewhat beyond. Bodies of high aspect ratio are also considered, where difficulties arise due to precision loss during numerical integration. Loss ranges from 4 or 5 significant figures (2:1 spheroid) to 22 figures (40:1 spheroid) or more. A class of surfaces has been found for which this problem can be avoided, however, enabling one to treat a variety of body shapes up to aspect ratios of 100:1 with no difficulty.