Prediction accuracies of ray-tracing and regression models in open-plan offices

The purpose was to determine the prediction accuracies of an empirical regression model (Model 1) and a ray-tracing model (Model 2) in acoustically different open-plan offices. The measurement data was obtained from an open-plan office (81 m2) in which 22 completely different room acoustic conditions were built using alternative room absorption areas in ceiling, walls, and screens, and alternative screen heights. The sound pressure level (SPL) produced by an omnidirectional sound source was measured in six positions in each condition. The corresponding SPLs in 22 conditions were predicted using Models 1 and 2. The prediction accuracies were determined for the A-weighted SPL of speech in each position. In addition, the prediction accuracy was determined for the basic quantities of ISO 3382 standard: spatial decay rate of speech, D2,S, A-weighted SPL of speech at 4 m distance, Lp,A,S,4m, comfort distance, rC, and mean reverberation time T. The mean prediction accuracy of A-weighted SPL of speech was 4.2 dB for Model 1 and 3.4 dB for Model 2. Model 1 predicted D2,S, rC, and T more accurately than Model 2, while the opposite ranking order was found for Lp,A,S,4m. The prediction accuracies of both Models were sufficient when the effects of sound absorption materials and screen heights is simulated. The finding suggests that simple empirical regression models can provide sufficient prediction accuracy in most room acoustic conditions of open-plan offices.