Know-How: Acoustics
Feb 1, 2005 12:00 PM, by Mike Kennedy
Creating a classroom environment in which students can hear and comprehend what a teacher or other students are saying will create a more effective learning environment.
“Classroom Acoustics,” a guide put together by the Acoustical Society of America, provides many suggestions for improving the listening conditions for students and teachers:
- Reverberation
Reducing the reverberation time (how quickly sound decays in a room) can improve acoustics. Decreasing the volume of a classroom or increasing the amount of sound absorption will reduce the reverberation time.
“Adding a suspended ceiling of sound-absorbing tile can significantly improve the acoustics by simultaneously decreasing the volume and increasing absorption,” the guide says.
- Equipment
Noise from mechanical equipment can detract from a student's ability to concentrate and learn. Avoid placing any major mechanical equipment “inside, above, below or adjacent to classrooms.”
- Windows
Windows may allow unwanted sound into a classroom.
“To provide noise reduction, windows must be well sealed,” the guide says. “Double-paned glass provides better sound reduction than single-paned glass.”
- Wall construction
In general, the thicker the wall, the greater the noise reduction.
“However, a thick, solid wall is usually too expensive and heavy and wastes valuable floor space,” the guide says. “An effective compromise is to construct a wall of a layer of heavy material, an airspace, and another layer of heavy material.”
- Sound system
Some classrooms can benefit from sound amplification; a teacher wears a microphone, and speakers amplify the speech.
“This can be useful in a room with a moderate amount of mechanical noise that would otherwise be difficult or expensive to silence,” the guide says. “However, such systems also have their limitations.”
For instance, amplified sound in a room with a high reverberation time may remain unintelligible, and such systems usually do not provide amplification for students. Using a combination of reflective and absorptive materials will provide the most effective acoustical conditions.
NOTABLE
Sound-pressure levels (in decibels) of common sound sources:
20
A whisper
50 to 70
Speech range
80
Cafeteria
100
Accelerating motorcycle
140
Jet engine (75 feet away)
Source: “Classroom Acoustics,” Acoustical Society of America
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