Road traffic noise is transmitted into an indoor space through a window opening for natural ventilation, causing noise annoyance of the occupants. Accordingly, it is important to predict sound transmission loss (STL) through the opening to estimate the indoor noise level distribution in a naturally ventilated condition. In a relatively short computational time, the ray-tracing method (RTM) is used to predict STL through the opening in urban spaces although the accuracy of the method in such situations needs to be examined. In this study, therefore, a finite element method (FEM) was used to investigate the accuracy of RTM on predicting STL through the opening. The predicted results were compared for the factors including opening sizes and incidence angles under a free field condition. The result predicted by using RTM showed a significant sound pressure level (SPL) difference compared to FEM results, especially for a relatively small opening at low frequencies and normal incidence angle. The prediction error for road traffic noise spectrum was within 3 dBA from the opening area above about 1000 cm2, indicating the possibility to use RTM to predict noise reduction through the window opening of a simple shape.
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