Ten years of classroom acoustical design

Abstract

Bradley found [J. Acoust. Soc. Am. 80, 837–845] with word score tests that S/N and room reverberation time (RT) affect speech intelligibility, and that computed U50 [J. Acoust. Soc. Am. 80, 846–854] was maximum for rooms having RT<0.6 sec and quieter than 35 dBA. This was applied to teleconferencing rooms [J. Acoust. Soc. Am. 111, 2411(A)], and classrooms for distance learning [J. Acoust. Soc. Am. 107, 2861(A)]. Economic strategies to reduce classroom RT and HVAC noise were developed. RT from 0.5 to 0.7 s and NC less than 30 are economically achieved: Absorption is provided by acoustical ceiling tiles of NRC>0.6. Carpets help. Chalk and cork boards provide some wall absorption, while in-use posters and book storage add more later. Central air handling systems promote NC-25 HVAC design. Noisy supply (VAV) air boxes are placed in the corridor ceiling. The transmitting manifold is lined. A flexible duct link to diffusers provides more noise attenuation at no added cost. Larger supply air diffusers satisfy NC-25. Common ceiling return air plenums compromise noise isolation between classrooms. High CAC ceiling tiles and return air openings near the room center provide NIC>40 versus recommended NIC50. Sketches and some cost estimates are provided.