Following the previous report in Internoise 2011, a field experiment had been continued for a year to investigate the effect of sound absorption on the comfortable acoustic environment of nursery school classrooms. Sound absorbing boards, made of polyester, were installed on the ceilings of the classrooms of an actual nursery school with their cover ratio to the ceiling area being set to 0, 40 or 80%. Noise levels were measured in the three time periods of lunch, reading and napping. The result indicated that the noise levels decreased in various combinations of the sound absorption conditions and that the level difference between 0% and 80% were 6-8 dB in some of those cases, which is greater than the expected physical reduction (approx. 3dB) estimated from the absorption coefficient of the board. Personnel of the school were asked to evaluate the indoor environment of the classroom and the answers were generally in favor of the absorbed conditions.
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