Partial diffraction ard scattering play an important role in the reflection of acoustic waves by a real-life wall surface. In the modelling of the acoustic sourd fields inside an enclosed space, the incorporation of such diffraction and scattering effects can greatly improve the accuracy of the modelling. In commonly used room acoustics prediction models, such as the image or the ray tracing methods, these effects are approximated by partial diffusion-by augmenting specular reflections with the so-called diffuse reflections. The fraction of acoustic energy that is reflected diffusely upon a wall reflection is related to a diffusion coefficient of the wall. Currently there are a number of different methods available to implement diffuse reflections in room acoustics prediction models, ard there is no single accepted way of defining the diffusion coefficient for a wall surface. This paper investigates the prediction characteristics of three commonly used diffuse reflection modelling methods ard attempts to establish the diffusion coefficient values of some common room surfaces. It also looks at the possibility of calculating the diffusion coefficient from the polar diffraction pattern of a surface ard some means of measuring the coefficient.