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Why Johnny Can’t Hear
November 28, 2000
This miniature classroom is used to study noise levels that children are subjected to at school.

Almost four million school-age children have learning disabilities, according to the National Institute of Mental Health. But that may not be the only reason some kids have trouble learning in school.

Studies have shown that many classrooms may simply be too noisy for students to hear what the teacher is saying. By observing classes and constructing classroom and computer models, a team of researchers from the University of Florida has recently shown just what your child may be missing, as well as what can be done about it.

Classroom work

"Research by audiologists and educational psychologists has shown that one of the major deterrents to learning, particularly with young children in the primary grades in schools, has been related to building acoustics," says Gary Siebein, professor of architecture at the University of Florida in Gainesville.

To find out more about classroom acoustics, Siebein and his team visited ten Florida classrooms for two to four hours each day over a two or three day period. The classrooms were representative of more than 5,000 classrooms in the state.

The study showed that in a noisy classroom, children can hear what the teacher is saying only at a certain distance. "We found in general that there is a critical distance of about 10 or 12 feet in a classroom," says Siebein. If students are located close to a teacher in an average classroom, they’ll be able to hear almost all of the words correctly. But once they get more than 10 or 12 feet away from the teacher, they’ll only hear about 20 or 30 or 50 percent of the words at best that the teacher is saying at any given time."

Measurements of classroom acoustics

The measurements were based on the impulse response technique, which is analogous to looking at how the room responds to sound. "So you can take a sharp loud sound, like a hand clap and look at the way the sound waves reflect off of each of the individual surfaces of the room...on their way to the ears of each student," Siebein explains. "And this is almost like a doctor who takes a cardiogram of your heart—where, by looking at the pulsing of your heart, he can make a diagnosis about your relative health."

The researchers collected enough data to piece together which surfaces contribute to acoustics that would increase the loudness of sounds and improve communication, and which ones produce reverberation that deteriorates communication, according to Siebein. The results were published last month in Language, Speech and Hearing Services in Schools, a publication of the American Speech-Language-Hearing Association.

Sound education

Not being able to hear every word is a particular problem for young students. "They haven’t fully developed the ability and cognitive skills to decode information the way older students and adults have," Siebein says. When adults are unable to hear something clearly, they can often fill in the gaps by drawing on their language experience, such as vocabulary knowlege, grammatical and sentence structure and previous knowledge about a topic. But children lack this experience. In fact, their speech recognition approaches that of adults only when they reach their teens. This means that young children could begin to lose interest in what the teacher is saying simply because they can’t hear what’s being said. This distraction could in turn lead to behavioral disruptions (talking when you’re not supposed to, getting out of your seat, interrupting, throwing paper airplanes, etc.).

Students with some type of hearing loss are obviously at a disadvantage. But even those with normal hearing may be affected if they have some type of learning disability or if English is a second language. What’s more, many children suffer from temporary hearing loss due to ear infections. With an estimated 75 per cent of the school day being spent on listening activities, it’s easy to see how children could fall behind if they can’t hear properly.

Addressing the problem

The University of Florida team found two main problems with classroom acoustics. The first was caused by excessive background noise due to heating, ventilating and air conditioning systems. The researchers noticed that in order to be heard in class, teachers would often turn off the air conditioner. "They couldn’t conduct normal classroom activities with the air conditioner on," says Siebein. The second problem was due to excessive reverberation, which is sound that bounces around the room from different surfaces.

Gary Siebien
Gary Siebien, professor of architecture at the University of Florida, Gainesville

According to Siebein, a noise level of up to 35 or 40 decibels, which would be heard as a fairly quiet room, seems to be about the point where hearing and learning can occur pretty well. But many of the rooms he studied had noise levels of between 50 and 55 decibels.

To find ways of improving communication, Siebein and his team built a one-fourth scale model of a typical classroom with adjustable walls and ceilings, as well as movable furniture. They also constructed a computer model to probe the various changes that could be made. "There are several changes that could be made to existing facilities, as well as features that can be added to rooms as they are being designed, that can improve communication and learning in the rooms," says Siebein.

Some of these include installing central heating and air conditioning, and carefully selecting materials for the walls and ceiling. Rooms being used for lectures, for example, would benefit from having ceilings made of both an acoustically reflective material such as gypsum board or plaster, as well as absorbent materials that would limit reverberation.

Other considerations include limiting ceiling height, installing carpeting, employing classroom furniture arrangements and teaching techniques that reduce the distance between the teacher and the students, using sound amplification systems where needed, selecting school sites that are isolated from major transportation and industrial noise, and designing special acoustics for certain rooms such as gymnasiums and cafeterias.

The American National Standards Institute is working on national standards that would limit the level of background noise allowed in newly built schools. But even existing schools can be modified to be more acoustically friendly at moderate cost, Siebein says. And money spent on these changes may turn out to have pricelesss educational benefits.

Elsewhere on the web

Access Board Partners with Industry on Improving Classroom Acoustics

Acoustical Society of America

Better Hearing Institute

National Center for Physical Acoustics

Learning Disabilities from the National Institute of Mental Health

Classroom Acoustics from the National Clearinghouse for Educational Facilities

The UK Quiet Pages

Institute of Noise Control Engineering



by Jill Max


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