Optimal reverberation time in classrooms

Optimal reverberation time in classrooms when the noise source are nearby pupils is in the range of 0.3-0.9 s, with a preferred value around 0.7 s, according to Yang and Bradley (2009). Optimal reverberation time for the speaker in a classroom is around 0.75 s, according to several studies in which we monitored teachers’ voice in primary and secondary schools. This study involved 29 occupied primary-school classrooms in Italy where speech level (LS) and Sound Strength total (Gtot), early (G50) and late (Glate), have been measured at 1 m from the source and in other three positions along the main axis of the room. The background noise level during the measurements was less than 56 dB(A) and the reverberation time (RT) was between 0.5 s and 1.4 s. A cut-off value of RT was assumed equal to 0.8 s for subdividing the classrooms in two groups of similar size, with lower or equal and higher RT values, respectively. The slope per double distance of the speech level along the main axis, mLS, and of the Gtot, is -2 dB/dd for both the groups, while it is -3 dB/dd for G50. Glate shows a slope of -0.6 dB/dd and -0.9 dB/dd for the two groups, respectively. Optimal reverberation time range, between 0.6 s and 0.9 s, has been obtained in the case of Glate-G50 at the rear positions is set between 6 dB and 3 dB, respectively, with a central value of 0.7 s. This optimal value agrees with the previous literature findings.