Besondere Reformprojekte: Unterrichtsformen

Jeffrey Chuang, Dallas Morning News (1) & Carolyn Edwards (2)

Noisy Classrooms May Hinder Learning, Experts Say

High classroom noise levels - from the incessant squeals of chattering children to loud machinery - may be affecting children's ability to learn.

In fact, some U.S. scientists now believe that one of the reasons Johnny can't read may be that he can't hear.

Classrooms often buzz with noise levels so high they impair a young child's speech perception, reading and spelling ability, behaviour, attention and over-all academic performance, researchers told a conference of the Acoustical Society of America.

"Some normal children, when put in an average classroom, break down tremendously," says Carl Crandell, an audiology professor from the University of Florida at Gainesville who presented a summary of sound scientists' recent findings at the conference.

In an above-average classroom listening environment, grade-school children with no hearing problems can make out only 71 percent of the words a teacher at the front of the room pronounces, says Crandell. In the worst environments, children can process just 30 percent of the sounds.

"It sounds like one big blur," says David Lubman, chairman of the classroom acoustics committee at the conference.

While the problem is quite severe for children in elementary shcools, poor acoustics go largely undetected by adults. "Children don't develop an adult-like ability to understand speech until they are 15," explains Crandell. "These rooms can just devastate them."

Classroom static can induce children to ignore any signals they do receive. The children learn to tune out not just the band blaring horns outside, but also the teacher. "If a child cannot hear, attentional and/or behavioral problems often occur. When we can get a child to hear well, we often see a reduction or elimination of those problems," says Crandell.

Over the past few years, a number of researchers have measured classroom noise with microphones, tested children's recognition of monosyllabic words in those rooms, and interviewed teachers across the U.S. Recently, Crandell began comprehensive tests in elementary schools.

Acousticians generally agree that a maximum sound level of 35 decibels is appropriate for a learning environment. But of the classrooms surveyed, many had sound intensities 30 times higher than the recommended level. Echoes persisted for a full second - twice as long as the cutoff suggested by the acoustical society committee to aovid interfering with teaching. The interviewed teachers frequently complained aobut distracting noise.

Concerns for hearing-impaired children prompted the first studies on classroom noise two decades ago.

But scientists did not realize until recently that many kids who did well on standard auditory tests were affected by poor classroom design as well.

Moreoever, one third of all children have some history of ear infection and that group has more problems dealing with noise, says Crandell.

One solution would be to fit the walls of classrooms with "acoustic tile," a material that absorbs unwanted noise the same way carpeting does on the walls of performance halls.

Jeffrey Chuang, Dallas Morning News

Many parents have felt that their children have done badly in child-centred classes. An article in the most recent edition of Vibes, a publication of the Canadian Hearing Society, may provide the answer. Ms Edwards does not give sources for her studies, but most of the work in this area has been done by Dr. Mark Ross and his team in the Audiology Department at the University of Akron - John Craig

Today's Lesson: Noise in the Classroom

While classroom design and materials have changed little over the past 20 years, there has been a significant change in teaching styles. Today's classrooms offer many different learning experiences: large and small group instruction, group projects and individual work. One of the side effects of child-centred learning approaches is increased noise levels in the classroom. The effects of noise on listening for children with hearing loss are well documented. The effects on children with normal hearing have received less attention.

The Problems

Children often report that they can hear the teacher well, even at the back of the class. They are correct. Speech continues to be audible at a distance for individuals with normal hearing and milder degrees of hearing loss. However, speech loses clarity as the distance increases. A 1991 study showed that the amount of speech energy was reduced by 45 per cent from the front to the back of a quiet classroom. When listening directly in front of a speaker, 97 - 100 per cent of the speech energy was received. In the third seat from the front, 69 per cent of the measured speech energy was retained, but at the rear of a typical classroom, only 55 per cent of the speech energy remained. When children with normal hearing were asked to repeat sentences in a typical classroom, scores were 89 per cent correct when the speaker was six feet away. Understanding dropped to 55 per cent at 12 feet away and 36 per cent at 24 feet away.

It's noisy in here

In a 1990 study, 54 per cent of classroom teachers and 77 per cent of physical education teachers surveyed reported that noise casued communication problems most or all of the time. Background noise levels vary with the type of activity, the number and age of students, the acoustical treatment of the room and the teacher's tolerance for noise. Unfortunately, the highest noise levels are often seen with the youngest students who are the least able to cope with the effects. The average intensity level of a teacher's voice in the classroom is 65-70 dBA. The typical classroom noise levels range from 55-77 dBA, although certain areas, such as computer rooms (73-79 dBA), cafeterias (75-80 dBA) and the gym (80-85 dBA) exceed these figures. From these measurements, it is clear that the teacher's voice is often only equal to the level of background noise, and may even be softer than the noise levels in the classroom.

Children versus Adults

Studies show that age has a significant effect on the ability to understand speech under less than ideal conditions, such as soft or muffled speech, speech at a distance or in a noisy environment. In fact, children need approximately a 10 dBA louder speech signal than adults to receive the same speech recognition scores as adults. When listeners are unable to hear well, they call on their experience with the language (previous knowledge about a topic, predicted vocabulary, grammatical and sentence structure) to fill in the acoustical gaps. Children in the process of building their language base do not have the same linguistic experience as adults. It is only when children reach their teens that their speech recognition under difficult listening conditions comes close to that of adults.

The effects of reverberation

Reverberation is the length of time that a sound continues after the sound has been produced. For example, the reverberation time is quite long in an underground garage and quite short in a library. As with other auditory skills, the ability to understand speech under reverberant or echoic conditions improves with age. Research has found that young children, particularly 4-7 year olds, obtain poorer speech recognition scores and demonstrate mose adverse behaviours than their older counterparts in rooms with higher reverberation. Unfortunately, the majority of classrooms today have reverberation times in excess of recommended standards for children. Only 28 per cent of classes surveyed in one study met the requirements.

School populations at a Risk

Studies have shown that all of the following groups of children have difficulty understanding speech in classsrooms with typical background noise levels and reverberation characteristics: young children with normal hearing; children who are non-native English speakers; children with:

• articulation problems
• language learning disorders and/or listening difficulties
• minimal hearing loss (16-24dB hearing loss)
• minimal high frequency hearing loss
• unilateral (one-sided) sensorineural hearing loss
• recurring ear infections
• mild to profound sensorineural hearing loss

Children in any of these categories show decreases of 10-40 per cent in understanding of speech, compared to their ability to listen in quiet.

Acoustic Design

Incorporating good acoustic design into new school buildings adds no more than one per cent to the total building budget, considerably less than the cost of retrofitting exising schools. Consultation with an acoustical engineer should be an essential part of the school design process. Construction considerations such as insulating between classroom walls and between floors of the building can reduce the amount of cross classroom noise. Simple modifications such as putting rubber stoppers on locker doors can reduce the amount of noise form the hallways. Carpet with underpadding is the best way to reduce the low- and mid-frequency components of noise. A key source of noise in the classroom is chair noise on uncarpeted floors. When carpet is not affordable or desired due to the respiratory needs of children, tennis balls placed on the legs of students' charis reduce chair noise considerably and have proved quite popular (cut a small X in a tennis ball and slip the chair leg into the hole created by the X).

Use of FM-technology

Amplification systems are now available for use in a regular classroom to address some of the listening and learning concerns resulting from poor acoustic conditions. The teacher wears a wireless FM microphone which transmits his or her voice to an amplifier and speaker system installed in the classroom. Use of FM systems can enhance the teacher's voice by 8 to 15 dBA and simultaneously reduce teacher vocal fatigue.

Conclusions

Poor acoustic conditions in classrooms can affect speech recognition ability, psychoeducational development, psychosocial development and teaching conditions. The incorporation of acoustical design into new school buildings, modifications to classroom acoustics, use of FM technology in regular classrooms and fostering children's listening strategies can address some of the concerns raised by the current acoustic conditions in classrooms.

Carolyn Edwards, M.Cl.Sc., M.B.A.
Director of Auditory Management Services, a private practice in educational audiology, Toronto.