High-performance acoustic ceilings make quiet classrooms quieter.

Highly beneficial noise level reductions of 5–10 dB are reported in occupied classrooms equipped with highly sound absorbing ceilings. The incremental cost for such ceilings is nominal. These “Lombard effect” benefits apply to small classrooms with very low reverberation times (0.5 s or less) which is less than the 0.6-s maximum specified in ANSI S12.60-2002. The amount of noise reduction depends on teaching/learning style. In the typical noise reduction lecture classrooms (single talker), the typical noise reduction benefit is 5 dB in lecture classrooms (single talker) and group learning classrooms (multiple talkers). Unfortunately, these benefits require unoccupied background noise levels (BNLs) of about 35 dBA. They are not expected in typical noisy American classrooms (BNL ∼>45 dBA). This underscores the importance of compliance with ANSI’s 35-dBA BNL limit rather than the lenient and unsupported 45-dBA limit permitted in recent LEED and California CHPS guidelines. Details are reported in the outstanding study “Acoustic Ergonomics of School” by Oberdorster and Tiesler [University of Bremen, Germany (2006)]. Similar benefits were reported earlier in a case study by Sutherland [“The role of soundscape in children's learning,” J. Acoust. Soc. Am. 112, 2412–2413 (2002)].