The effectiveness of the classroom relies on many things, one of which is making sure students can hear what is being said. Listening plays a vital role in our personal and professional lives by providing people with the ability to learn. However, a growing body of research confirms that many students cannot hear clearly and comfortably in class.

Research studies are indicating that listening in classes is diminishing due to students' lack of attentiveness and excessive "off-task" talking behaviors. This off-task talking behavior can lead to increased levels of noise, and decreased levels of listening and learning for students in classroom environments.

Researchers appear to be conclusive that increased noise in classroom environments can decrease listening, and they suggest that this lack of listening may not be entirely the fault of students. The lack of listening may be due to students' inability to know how to filter out unwanted noises that prevent them from listening in the first place.

In a recent study conducted by the Centers for Disease Control and Prevention published in the Journal of the American Medical Association, researchers tested approximately 6,100 children between the ages of 6 and 19 for hearing loss. Nearly 15 percent of the children had some form of low-frequency or high-frequency hearing loss. Low-frequency hearing problems affect the ability to understand speech, while high-frequency impairments make it difficult to hear high-pitched sound.

Audiologists add that even students with no impairments whatsoever may have difficulty hearing what a teacher says in a modern classroom. The reasons include poor acoustical design of classrooms and noise from heating, ventilating and air-conditioning systems, combined with teaching methods. Students with any kind of hearing, attention or second-language problem will find it difficult to focus.

Raising awareness Poor acoustics affect everyone, but certain vulnerable groups are disproportionately affected. These include the hearing- and learning-disabled, and those with limited English proficiency. Proper design can help schools avoid acoustical problems, and current knowledge can correct problems. Fixing the problems may improve academic performance and teacher morale, and lead to fewer dropouts and disciplinary problems, especially among marginal students.

Architectural features that please the eye can bounce sound around the classroom so much it can be difficult for some students to concentrate. In this case, when just a few people are talking, the room is noisy. Simply put, students sometimes have a hard time hearing what their teachers are saying. The reason is that schools frequently are not built with listening in mind. Classrooms often have hard floors, concrete walls, lots of windows, high ceilings and chalkboards that cause sound to reverberate and distort. In addition, there are plenty of noisemakers at schools: passing traffic, playgrounds, ventilation systems, scraping chairs, slamming doors and the children themselves. Sometimes, even the layout of a school can cause problems.

One study found that students with normal hearing, in a classroom with above-average acoustic design, understood 71 percent of what the teacher said. However, hearing-impaired students could only understand 48 percent of what the teacher said. Students who cannot hear the teacher well may not understand their lessons. Often, many of these children become bored because they do not know what is going on, and theybecome disruptive. Noise and reverberation also can cause voice fatigue among teachers, who have to constantly raise and lower their voices depending on the noise levels in their rooms.

The problem The school environment is filled with various sounds from a variety of sources. Some of the sounds are desirable and are called "signals." Other sounds are not desirable and are called "noise." This relationship often is referred to as a signal-to-noise ratio or S/N ratio. The teacher's voice, for example, is the signal, and competing voices or other sounds are the noise. Usually there are more noises than signals. Classroom acoustics are based on three factors: ambient noise level, reverberation time and S/N ratio.

Open windows or windows not designed to be acoustic barriers increase the ambient noise level of a classroom by letting noise from lawnmowers, street traffic and playground activity enter the room. Interior ambient noise includes other students, computer equipment, heating systems, music and faulty equipment.

Since the signal is what people want to hear and noise is what is interfering, it is desirable to have the signal considerably stronger in intensity compared to the interfering noise. When sound bounces around the room by reflecting off different surfaces, it causes noise to build up in intensity, and the signal is smeared. This process is called reverberation. Reverberation time (RT, sound echoed off smooth surfaces, such as walls or ceilings) is the time required for a sound, introduced into an environment, to reduce its intensity once the sound is shut off. Rooms with hard, uncarpeted floors, reflective walls and high ceilings tend to have long reverberation times. On the other hand, rooms with sound-absorbing surfaces, such as carpet, acoustic tile and curtains, will have shorter reverberation times.

One solution Over the past 15 years research has shown that FM sound-field amplification is one effective way to produce change in students' listening behaviors and academic achievement. A sound-field amplification system operates like a wireless public-address system and can be installed easily in less than five minutes. The teacher wears a microphone that is attached to a small FM wireless transmitter and sends a radio signal to receivers built into several speakers around the room. The amplifier is set, and the loudspeakers are positioned to create a positive SNR (approximately +15 dB) in all listening areas of the classroom. This means that the signal is always louder than the noise. Acoustically speaking, the system puts every student in the front row.

Recent studies have indicated that students in classrooms with sound-field equalization showed significant improvements in Scholastic Reading Achievement scores. For example, one five-year study reported a 40 percent decline in students identified as learning-disabled in classrooms using sound-field amplification systems. This study also reported that children working in amplified kindergarten classes scored better in listening, languages and vocabulary test scores. First-graders performed better in language studies. Second-graders did better in math, and third-graders turned in better scores on both math and reading tests.

Anything that helps children learn in a cost-effective and positive way should be of interest to all educators and parents. For instance, sound-amplification systems can be purchased inexpensively, and the systems will not become obsolete like other technologies, such as computers.

Issues that should be discussed with a school architect regarding existing instructional spaces, renovations or new spaces:

-Can classroom acoustical environments be improved sufficiently through design and construction measures to significantly benefit students with hearing impairments?

-What other design variables, such as room configuration or proportion, should be considered to improve classroom acoustics?

-What are effective means of acoustically retrofitting an existing classroom or other space that performs poorly for speech perception?

-What additional square-foot cost would be necessary to meet various recommendations for reverberation time and/or background noise for classrooms?

-What data are available on the costs of alterations to existing environments to improve acoustical conditions?

-What approaches, other than ADA regulations, might be successful in achieving good acoustical design?