The paper presents a number of problems related to sound reflections, and possible solutions or approximations that can be used in computer models. The problems include: specular and diffuse reflections, early and late reflections, curved surfaces, convex and concave surfaces, diffraction due to finite size of surfaces, scattering due to rough structure of surfaces, angle dependent absorption, phase shift at reflection, surfaces divided into reflecting and absorbing parts, partly transparent surfaces, reflector arrays. Due to the wave nature of sound it is very important for the quality of a simulation model that diffusion and diffraction effects are included in a proper way. This is demonstrated through some examples, which also indicate how good results can be obtained with a minimum of calculation time.