Direct application of the diffusers’ reflection patterns in geometrical acoustics simulations

•Use of detailed reflection models improves the room acoustics simulations results.•The change caused by more accurate reflection modelling is significant in the early simulation stage.•The proposed A-BRDF based reflection model allows for diffuser comparison and selection. Using the combination of specular and Lambert reflections is a common technique for modelling reflection in room acoustics simulations. Diffusing surfaces are simulated indirectly using scattering coefficients, describing the ratio between a specular and Lambert part. Such technique has two main flaws. The ideally specular reflection cannot simulate the reflection redirection, where a strong reflection appears on direction other than mirror. Simultaneously, the Lambert model is accurate for scattering simulation only in diffuse field conditions. Otherwise, the actual scattered distributions may differ significantly from Lambert model. This paper focuses on the direct usage of diffuser reflection patterns in the geometrical acoustics simulations. A general approach for the application of any reflection pattern in computer simulations is described and the procedure for creating reflection models based on the surface geometry is presented. The results obtained using the combination of specular and Lambert reflections are compared with the ones obtained using the proposed approach. We also analyse the impact of the chosen diffuser and modelling technique on the sound pressure level distribution and common acoustic parameters within the simulation. The results prove that the proposed method can reproduce reflections with significantly higher accuracy compared to use of specular and Lambert model combination. It is also shown that using more exact reflection model significantly affects the early stage of acoustic field formation in a room.