Abstract
Field measurements of background noise levels produced by air-conditioning systems were taken in a sample of 47 elementary school classrooms. Noise levels were grouped by air-conditioning system type and resulting noise criterion (NC) levels. Eight computer models of classrooms were constructed with varying combinations of absorbent materials on the surfaces of the rooms. A sound source was configured to approximate the normal speaking voice of a teacher in the room. RASTI measures were estimated for six seating locations in each room for background noise levels from 0 dB to NC- 55 in 5-NC point increments. RASTI values remained above 0.8 in seven of the eight rooms at NC levels of 32 and below. RASTI levels decreased to 0.50 and less in all eight rooms at levels of NC- 45. The one exception to this was the room constructed with a gypsum board ceiling, vinyl tile floor, and gypsum board walls. Even with no background noise, RASTI values in this room never exceeded 0.60. Background noise levels of NC 32 or less appear to be necessary in most typical classrooms to maintain reasonable RASTI values. Very few of the actual classrooms visited achieved these noise levels.
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