Predicting classroom acoustical parameters for occupied conditions from unoccupied data

This paper introduces a simple procedure for estimating the effects of occupants on the acoustical characteristics of university classrooms. Values of room acoustics parameters such as EDT, C50, G, Glate, STI and U50 are useful indicators of the quality of conditions for speech in rooms intended for speech communication. It is more difficult to measure these parameters in occupied spaces and hence being able to predict occupied values of these acoustical parameters from unoccupied measurements is a great asset to achieving acoustically successful classrooms. In this work it is shown that the changes at 1000 Hz of EDT, C50, Glate, and U50 values, due to adding occupants, can be linearly related to the corresponding changes in total room sound absorption at 1000 Hz. It has also been shown that changes in total room absorption due to adding occupants can be simply related to the total unoccupied room absorption. Combining these two relationships provides a simple procedure for predicting the values at 1000 Hz of EDT, C50, Glate, and U50 values in occupied classrooms. These new procedures make it possible to design better classroom acoustics and to better understand acoustical problems when they occur.