Abstract Room acoustic design has a very important role to enhance objective and subjective characteristics of the space. Acoustic simulation before implementation is one of the main steps. Boundary Element Method (BEM) is the most accurate method in indoor sound field predictions. In this dissertation we have implemented BEM for predicting sound field inside a room (especially for this research). To provide some basic validation of the accuracy of the numerical models, sound field measurements were carried out in two rooms. The measurements results show great accuracy of the implemented program. Distribution of diffusive and nondiffusive surfaces on room walls affect sound diffusion in room, but the amount, combination, and location of these surfaces are still the matter of question. We investigated effects of these issues on room acoustic frequency response in different parts of the room with different source-receiver locations. Different distributions of acoustic surfaces on room walls have been introduced to the model and room frequency response results are calculated. Finally for more smooth frequency response in small and medium rooms, some suggestions are made. Then, evaluations of the predictions from the room acoustic modeling program have been run using two source types with the same sound power: (a) an omni-directional source; (b) a realistically-directional source with different directionalities together with different combination of diffusive surfaces on room’s walls. The results also confirm the relation of sound diffusion to surface diffusivity and show what combinations of surface diffusivity and source directivity could lead to a more smooth frequency response. The written program is also capable of predicting the scattered sound from diffusing surfaces like schroeder’s. Some of the predicted results of some diffusers are presented. | 
