Intelligibility in classrooms

Abstract
When e.g. an auditorium, lecture room or theater has to be judged acoustically, one will find the reverberation time plays an all-important part. In reality the reverberation time is a secondary size. The primary is the intelligibility of speech. It is shown, how it is possible in a school room not only to rate the intelligibility of the teachers speech towards the students, but also give an indication of where to put up absorbing material, which will improve the intelligibility. To install absorbing material in the middle of the ceiling for example, will have a damaging effect on the intelligibility.