Classroom acoustics design guidelines based on the optimization of speaker conditions

School teachers suffer frequently from voice problems due to the high vocal load that they experience and the not-always-ideal conditions under which they have to teach. Traditionally, the purpose of the acoustic design of classrooms has been to optimize speech intelligibility. New guidelines are suggested in order to optimize the vocal comfort and the vocal load experienced by speakers.

Theoretical prediction models of room-averaged speaker-oriented parameters like voice support or reverberation time derived from an oral-binaural impulse response are combined with empirical models of actual voice and noise level measurements in classrooms. Requirements of optimum vocal comfort, average A-weighted speech levels across the audience higher than 50 dB, and a physical volume higher than 6 m3/student are combined to extract optimum acoustic conditions, which depend on the number of students.

These conditions, which are independent on the position of the speaker, cannot be optimum for more than 50 students. For classrooms with 10 students, the reverberation time in occupied conditions shall be between 0.5 and 0.65 s, and the volume between 60 and 170 m3. For classrooms with 40 students, the reverberation times shall be between 0.7 and 0.75 s and the volume between 240 and 280 m3.