Performance of the buildings has always been a concern for the architects. With the enhancements in the technology, it is possible to measure, analyze and evaluate the performance of an architectural design before it is built via simulation tools developed. With the evaluation of the analysis performance of the concerned space can be upgraded if simulation tools are employed throughout the design process. However, even though the simulation tools are developed for the acoustical simulation and performance analysis, it is not always simple to integrate the simulation tools to whole design process because of both specific knowledge required for the usage of the tools and the nature of the acoustical simulation tools. For that matter, a simulation tool, which does not require advanced knowledge on acoustics, and which provides rapid feedback about the performance of the design for the enhancement of the performance, is developed using method of image sources. These works can be regarded as humble attempts to resolve the problems mentioned above. Hence, the tool itself and the scope of the work should not be perceived as a finalized project but as a model to be served for future works.