A Model for Calculating Reverberation Time, Speech Clarity and Sound Strength in Ordinary Rooms

A common acoustic treatment for ordinary public spaces, such as schools, offices, and healthcare facilities, is a suspended absorbent ceiling. The non-uniform distribution of absorption and the effects of furniture and interior fittings in these rooms present challenges for calculation models and simulation software. Furthermore, the acoustic data provided by manufacturers is often limited to a practical absorption coefficient, which is insufficient for the accurate characterisation of acoustic conditions. This paper presents an energy model for calculating room acoustic parameters such as reverberation time, speech clarity, and sound strength. The energy decay calculation is based on subdividing the sound field into grazing and non-grazing parts. The grazing part refers to sound waves that propagate almost parallel to the ceiling. This approach accounts for the ceiling’s angle-dependent absorption, as well as the scattering and absorption effects of furnishings. This model improves on and simplifies an earlier model. For practical use, tables are provided for grazing ceiling absorption and the absorbing and scattering effects of furnishings. The model has been validated by comparing it with measurements taken in 45 different room configurations. The new model produces results that are more in line with measurements than the classical Sabine model.