Acoustical measurements were performed in 30 randomly chosen, unoccupied cl
assrooms at the University of British Columbia (UBC). Tests had previously
been done in 46 unoccupied UBC classrooms, as well as in 10 of these when o
ccupied by students. The results for the 10 classrooms were used to correct
the "unoccupied" results to the half-occupied and fully occupied condition
s. The objective of the work was to characterize the 30 classrooms, which w
ere used in subsequent studies, to determine the acoustical quality of the
UBC classroom stock and how this depends on the classroom design and the pr
esence of students, and to elucidate characteristics of classroom acoustics
relevant to optimal design. The results showed that the UBC classroom stoc
k is of far from optimum acoustical quality when unoccupied, but is much be
tter in the occupied condition. Generally, many classrooms have excessive r
everberation and result in low speech levels, especially at the back of tbe
rooms; in addition, they have excessively noisy ventilation systems. (C) 1
999 Acoustical Society of America. [S0001-4966(99)00510-X].