Scientists Trying to Improve Acoustics in Classrooms

Nov. 12, 2001 -- On days when her class microphone is in for repair, teaching becomes a strain for Lizette Adkisson.

Adkisson has used the wireless microphone to talk to her 20 students over the din of a rumbling air conditioner ever since she started teaching third grade at the Fenton Avenue Charter School in Lakeview Terrace, Calif., five years ago.

Without the microphone, she senses her students drift away.

"I feel the children, especially in the back can't hear me unless I speak up," she said. "And my voice feels very tired."

Microphones Not a Final Solution

Over the past decade, schools in states across the country, including Florida, New York, Washington and California have installed microphones and speakers in the classroom to help students hear their teachers.

But many acoustical engineers say the microphones are a Band-Aid solution to a critical problem that seriously impedes a student's ability to learn.

"Wearing microphones is a solution if using crutches is a solution to broken legs," said David Lubman, an acoustical consultant based in Westminster, Calif. "When classrooms are reverberant — amplification doesn't help. It makes it louder, but not clearer."

Rather than forcing teachers to speak up over interfering noise, it's time school officials made classrooms quieter, Lubman and others argue

To spur improvements, a team of school officials and acoustical experts is putting together a list of acoustical standards to be adopted by the American National Standards Institute early next year. The hope is that schools will voluntarily try to meet them.

Lubman is also pushing to include the standards in the International Building Code, which would require all new schools or learning centers built after 2003 to adopt them.

What Was the Question?

Studies have shown that classrooms can be a hard place to listen.

University of Florida acoustics professor Gary Siebein has visited 26 different schools and about 600 different classrooms and discovered that 50 percent of the student population could not hear past the first two rows of their classrooms.

A University of Kansas analysis found that the speech intelligibility rating in most U.S. schools is 75 percent or less, meaning listeners with normal hearing can only understand 75 percent of spoken words.

Many European nations have already tackled the problem. Germany, Britain and Sweden all have mandatory acoustic standards for their classrooms.

Under the new U.S. guidelines, classrooms would need to keep noise levels below 35 dB (decibels), or as Lubman describes, about the sound level of a quiet country living room. Lubman's studies show that most classrooms in the United States have a sound level of 45 dB or more.

The main culprits in classroom noise (besides boisterous students) are heating and ventilation systems. Adding filters to ventilation systems can dampen noise, says Lubman. Widening air ducts also help since slow-moving air makes less noise than air flowing swiftly through narrow pipes.

Class Echoes

Another hindrance to hearing is reverberation, or how much sound is echoed in a room. The new standards call for keeping reverberation in a typically sized classroom below six-tenths of a second, meaning sound would be completely absorbed within that time.

For the same reason that train and subway announcements are often hard to understand, speaking up or using a microphone in a classroom with high resonance often only creates more confusing noise.

Rugs can help this problem, if they're thick enough. But most effective, says Lubman, is installing a fibrous material, like pressboard below the ceiling. The air pocket created between the ceiling tiles and the actual ceiling absorb sound.

Another way to improve reverberation levels is to alter the shape of the classroom. Abigail Stefaniw, an architect at Rensselaer Polytechnic New York, has conducted surveys and discovered that people find it easier to hear in trapezoidal rooms than in rooms designed in a typical shoebox shape.

Hearing Problems Are Widespread

Some students are more affected by poor sound quality than others. Students who speak English as a second language, for example, need to hear the precise enunciation of their teachers. But almost all children experience hearing problems at one time or anther.

A recent study by the American Medical Association found that 18 percent of the U.S. student population on any given day suffers from mild hearing loss caused by things like congestion or ear infections.

Ken Ulrich, a clinical audiologist with an eye and ear clinic in Wenatchee, Wash., has shown that students' scores drop precipitously as their ability to hear is degraded.

He's among those calling for better acoustic standards in classrooms, but he also believes putting microphones in the classrooms could help in the meantime.

"It's time something is done. Obviously we can't afford to rebuild every classroom in the country," he said. "But kids can't learn if they can't hear. It's like teaching them to read in the dark."