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- 2004-12-26
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The 500000-square foot school is located in Manchester, New Hampshire, north of Manchester Airport, about 0.6 miles north of the straight-line departure flight track form runway 06.
The school is comprised of three one-story wings and a multipurpose room (auditorium/cafeteria/gymnasium).
The building wings are oriented differently relative to the aircraft flight track.
Two wings (A and B) and the multipurpose room have brick and concrete block walls, but the third, newer wing (C) has pre-cast concrete panel walls.
The exterior walls in the two original wings were comprised of aluminum wall panels with two casement windows per classroom.
Glazing occupied approximately 15 percent of the exterior wall area in a typical classroom.
In the third newer wing, each classroom only has one awning window that occupies about 9 percent of the classroom exterior wall.
The roof-ceiling assembly consists of a flat metal deck roof with a suspended acoustical tile ceiling.
The school had a heating system but not central air-conditioning.
Figure 1 shows a typical curtain wall system at A-and-B-wing classrooms.
Figure 2 shows a typical exterior wall of a C-wing classroom.
2.2 Noise Level Reduction Testing
Initial noise reduction measurements were conducted at the school in June 2001 to assess the pre-modification acoustical characteristics.
These tests were performed before an asbestos abatement project began for which the existing ceiling tiles were removed.
Three representative classrooms (one in each wing), an interior conference room, and the multipurpose room were tested using an interior sound source technique.
The test procedure consisted of activating amplified loudspeakers inside each room and producing a high-amplitude pink noise signal.
The signal was filtered using an equalizer to produce a typical aircraft departure noise spectrum in the tested room.
Each sound source consisted of a JBL Eon Power 15 powered loudspeaker, an Ashly GQ215 equalizer, and an live Electronics IE-20B noise generator.
Average A-weighted sound levels inside and outside the tested rooms were measured using a Larson-Davis Laboratories Model 820 integrating sound level meter.
The microphone was swept throughout the main volume of the room and outside the building near the exterior elements.
The difference between the average interior sound level and average sound levels measured outside each exterior element was a measure of the existing Noise level Reduction (NLR) provided by the element.
Upon completion of the measurements, the overall NLR as calculated for each tested room based on the individual NLR values measured for the different exterior elements and the respective areas of the elements.
Table 2 summarizes the results of the measurements.
Table 2. Pre-Modification Noise Level Reduction
Room Noise Level Reduction(dB
Classroom 3A 24
Classroom 6B 25
Classroom 7C 25
Conference Room 1C 28
Multipurpose Room 20 |
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