Effect of sound absorption on indoor sound environment of nursery school classrooms

This study attempted to investigate the effect of sound absorption on indoor environment for infants in nursery schools. The expected effects were reduction of noise level and improvement of speech intelligibility, and consequently lowered voice level of infants, which is known as Lombard effect. Polyester fiber boards were installed on the ceilings of three classrooms of a nursery school, which are the rooms for 0, 2, and 4 years age, and the noise levels were measured before the installation and over four months after the installation. Acoustic measurements before and after the installation were also conducted to see the physical effect of the sound absorption. The averaged absorption coefficients of the three rooms before and after installation, calculated from the measured reverberation time, were from 0.16-0.17 and 0.29-0.30 respectively at 1000Hz octave band. Noise levels in a day were analyzed with the Leq of the three time periods of lunch, book reading, and nap, which represents the noisiest period with children’s voice, teacher's voice, and background noise, respectively. The noise levels before the installation were around 75-79 dBA in lunch time. After the installation the lunch time noise level in 0 and 2 year age room became 6-8 dB lower than that of before the installation, while that of 4 years age room didn't change much over 4 months after the installation. Since the expected physical noise reduction by sound absorption was around 3 dB, observed noise reduction in 0 and 2 year age room was considered to be caused by the lowered voice levels of the children and teachers, which were possibly a consequence of speech clarity or Lombard effect.