Sound propagation and strength in small classrooms

The 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 acquired 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 slopes per double distance of the speech level along the axis, mLS, is-2 dB/dd for both the groups. The same slope per double distance is obtained for G50 of-2.7 dB/dd, while Glate shows a slope of-0.6 dB/dd and-0.9 dB/dd for the two groups, respectively. The slope per double distance of Gtot is-2.0 dB/dd as in the case of the speech level, mLs, as expected. Optimal reverberation time range, between 0.6 s and 0.9 s, in occupied conditions, has been obtained from the difference Glate-G50 at the rear positions between 6 and 3 dB, respectively.