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