Effect of occupancy on acoustical conditions in university classrooms

Acoustical measurements were made in 12 university classrooms with and without occupants at Kangwon National University (KNU), Korea to investigate how the occupants influence the acoustical conditions of the classrooms. The mean sound absorption per occupant was calculated from the measured T30 values and compared in two different groups of classrooms (6 reflective and 6 absorptive classrooms). At 250 and 500 Hz, the mean sound absorption per occupant was nearly the same for both groups of classrooms, but not in the other octave bands. The results showed that the effect of the added absorption of occupants is dependent on the acoustical conditions of the classroom. The changes in acoustical parameter values, due to added occupants in the classrooms, tended to be largest for the more reflective classrooms. The occupants may contribute to achieving more ideal reverberation times for speech (typically 0.4–0.7 s in classrooms) in the more reflective classrooms, but not in the more absorptive classrooms. A simple process is described to predict the expected effects of adding occupants to other classrooms based on the total sound absorption of unoccupied rooms.