Inside: Acoustics

July 1, 2008
Retrofitting noisy classrooms; adopting acoustics standards.

Retrofitting noisy classrooms

Schools can't always eliminate noise that can make hearing and learning more difficult, but renovations can improve the acoustics in a classroom.

In a “Listening for Learning” fact sheet, the U.S. Access Board has compiled several suggestions for improving classroom acoustics:

  • Windows: Add storm windows; replace existing windows with thermal insulating units; install specially fabricated sound-reducing windows.

  • Doors: Add good-quality drop seals and gaskets; replace doors with tight-fitting, solid-core doors with seals and gaskets; install sound-control doors if adjacent spaces are very noisy.

  • HVAC: Add a custom-built sound enclosure around the unit; add soundlining to ducts; rebalance system to reduce air volume delivered to the classroom; relocate ductwork and diffusers away from teaching locations.

  • Excessive reverberation: Replace existing ceiling tiles with tiles that have a high noise-reduction-coefficient rating; add suspended acoustical tile ceiling if room height permits; add sound-absorbing panels high on walls at sides and rear of room.

Software solution

A professor at the University of British Columbia in Vancouver has developed a software program that can help school designers predict how well a teacher's voice can be heard in different parts of a classroom.

Murray Hodgson, a professor of occupational and environmental hygiene and director of the university's Acoustics and Noise Research Group, says the program, which he calls ClassTalk, allows architects, engineers and acoustical consultants to “design the noise out of classrooms.”

The software allows users to “walk through” the classroom by moving a “receiver” icon across a computer monitor.

At each position in the classroom, the program calculates and displays measurements in five areas — speech intelligibility, speech-transmission index, signal-to-noise level difference, speech level and background-noise level.

At any point, the classroom data can be altered to change room characteristics or introduce sound-control measures.

Hodgson and his associates also are working on a virtual-reality feature that would allow users to walk through the virtual classroom while listening to a teacher talking.

More information on the software is available at

Adopting new standards

The Minnesota Senate Education Committee has approved a bill that would require school districts planning new classroom construction or renovation to follow guidelines set by the American National Standards Institute (ANSI) for classroom acoustics.

If the bill becomes law, it would require newly constructed schools to have unoccupied classrooms with a maximum background noise of 35 decibels and reverberation time of 0.6 to 0.7 seconds.

The standards developed by ANSI are voluntary unless they are incorporated into regulations, as Minnesota is attempting to do. The U.S. Access Board, responding to a complaint from the parent of a student with a hearing disability, worked with the Acoustical Society of America to establish standards for classroom acoustics.

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