Dec. 24, 1999 COLUMBUS, Ohio -- Researchers at Ohio State University have found that the acoustics of many classrooms are poor enough to make listening and learning difficult for children.
The study of 32 classrooms in central Ohio primary schools found that only two met the standards recommended by the American Speech-Language-Hearing Association (ASHA).
“This is probably the most extensive acoustical study of classrooms ever,” said Lawrence Feth, professor of speech and hearing science at Ohio State.
The findings held across economic boundaries. In rural, urban, and suburban classrooms -- old school buildings and new -- background noise and echoes were prominent enough to hamper the learning of children with even mild hearing problems, according to the ASHA recommended levels.
“One of the worst classrooms was in a school district that had some of the better classrooms,” said Gail Whitelaw, adjunct associate professor of speech and hearing science. “So you can’t just say the acoustics in a district are good or bad. It varies by the room. It’s like real estate -- what matters is location, location, location.”
The researchers pointed to previous studies which showed that children’s learning and speech capability is hindered when they can’t hear well in the classroom.
Feth explained that sound bounces off of hard surfaces, and classrooms normally have hard floors and walls. “When sound bounces around it creates its own masking noise, and interferes with understanding speech,” he said.
Whitelaw said that children are sensitive to bad acoustics because they are still learning language, while adults’ larger vocabulary helps them mentally compensate when they can’t hear clearly.
“It only takes a small change in speech to noise ratio for a child to go from understanding almost everything to understanding very little,” said Feth.
Children with hearing problems or for whom English is a second language have an especially hard time following what a teacher says in a noisy room, the researchers said.
“Even if kids have temporary hearing loss from an ear infection, and even if it’s intermittent, it presents a big problem for understanding speech in a noisy environment,” said Feth.
Heather Knecht, formerly a graduate student, initiated this project, and Whitelaw and Feth were her advisors. Knecht, now a practicing speech-language pathologist in Dayton, Ohio, presented these results recently in Columbus at a meeting of the Acoustical Society of America.
Knecht measured the background noise level and reverberation time in 32 randomly chosen classrooms in eight central Ohio schools, some public, some private.
The ASHA guidelines recommend that sounds dissipate in 0.4 seconds or less, and that background levels not rise above 30 decibels(A). Feth said the decibel(A), or dB(A), unit is different than a plain decibel in that the dB(A) gives more weight to frequencies between 500 and 3,000 Hertz -- the ones that most affect how humans perceive loudness.
Feth said typical background noise in an office would average about 60 dB(A). Previous research has shown that noise in classrooms often rises to the same level.
Knecht measured background noise in empty classrooms after school hours to record the bare minimum sound level. Then, with a combination sound generator and sensor, she created a 120-decibel boom in each classroom, and measured the amount of time the sound took to dissipate. Feth characterized 120 decibels as what someone would hear standing right in front of the speakers at a rock concert.
Only two of the 32 classrooms Knecht tested met the ASHA guidelines for both background noise level and reverberation time. The background noise ranged from a low of 28 dB(A) to a high of 68 dB(A). The shortest time for reverberations to dissipate was 0.2 seconds, the longest time 1.27 seconds.
Background noise and reverberation weren’t necessarily connected, the researchers found. For example, one room had a reverberation time of 0.4 seconds -- within ASHA guidelines -- but a background noise level of 50.3 dB(A) -- more than 20 dB(A) too high.
Feth said the biggest single source of background noise in classrooms is the heating and cooling system, because many schools have opted for individual units instead of quieter central air.
Carpeting also helps buffer sound, but may be hazardous to children with allergies or asthma. For $1000 per classroom, a commercially available assistive listening system could do the trick, but that might be too expensive for some schools. Feth and Whitelaw listed some less expensive alternatives, such as draperies, wall hangings, or sound-absorbing panels.
“Educational audiologists perceive these changes as standard fare,” said Whitelaw, “but for school administrators it’s still a hard sell, because if they have to pull that money out of their budget, where will it come from?”
Whitelaw and Feth will continue this research, focusing on the relationship between room size and sound quality. They also want to find out whether the teachers who work in classrooms with poor sound quality experience more voice fatigue and take more sick days because they can’t talk.
Brüel & Kjær, a maker of sound and vibration equipment, provided the testing instruments for this study.
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