David A. Collings PE
The Impact of Room Acoustics on Classroom Communication.
Although school classrooms have seen many changes in recent years, teachers still rely on the spoken word as the principle channel for communicating with their pupils. The effectiveness of the teachers' efforts may depend on many factors, not the least of which is the recipients' ability to hear and correctly interpret the stream of verbal messages.
With today's emphasis on inclusion in the classrooms, a percentage of the students in any group is likely to be handicapped in language or cognitive abilities. This can place critical demands on the teacher's communication skills. The acoustical environment is known to play an important role in speech intelligibility and a classroom with poor acoustics may present a serious obstacle to learning even for normal children and especially for those with auditory or processing deficits.
Speech may be defined as a sequential array of sounds with varying pitch, duration and spacing, generated by the vocal cords, lips and tongues of the speaker. In order for speech to be heard and correctly interpreted, the sounds must reach the receiver's ear in roughly the same pattern as the original transmission. The human brain has a remarkable ability to decode and compensate for imperfectly received auditory patterns. A listener also relies on visual cues (e.g. the speaker's body language) to complete his understanding of the message. An experienced teacher may adjust to a poor acoustical environment by slowing or emphasizing his or her delivery and by repetition, facial expressions and gestures. The ability to compensate in this manner however will vary between individuals and is likely influenced by factors such as age, culture and national origins.
The demands placed upon both speaker and listener in a classroom environment that distorts or masks normal speech patterns are believed to have long term effects on the learning process that may not be measurable by simple observation. The negative effects are likely to be significantly greater for students with impaired hearing or cognitive disabilities. It has been recognized that young children have immature decoding abilities that can seriously handicap their progress at a critical phase of their development if they are taught in a hostile acoustic environment (1).
The critical parameters that affect the transmission of speech in a room are the signal to noise ratios (S/N) and the reverberation times (RT) measured over the normal range of speech frequencies. Background noises in a classroom environment can be from external sources, e.g. aircraft and road traffic, or internal, from room air conditioners, ventilation fans or student activities. Reverberation in a "hard" room lacking adequate sound absorption can exacerbate the background noise but more significantly, many speech components are masked or distorted by delayed reflections. New guidelines and standards for classroom acoustics have been drafted recently by a number of specialists and professional groups in response to a petition published in the Federal Register in June 1998. Such guidelines may eventually become federal requirements under the Americans with Disabilities Act.
Voice amplification has been widely promoted as a cure for poor speech intelligibility in classrooms. These "Soundfield" systems appear to offer a simple fix for a room with a high background noise level. However, although voice amplification will improve the teacher's S/N ratio, communication between the students may still be poor. No electronic device can correct for the high reverberation time that may exist in many learning environments. In order to provide optimum conditions, classrooms should be professionally evaluated and brought to an acceptable standard before installing an amplification system.
Typical reverberation times measured in a good modern elementary school classroom are shown below: -
The above measurements were taken in an unoccupied classroom. The flooring was uncarpeted hard vinyl but the ceiling was a high quality suspended acoustical tile. Experiments with FM voice amplification in this classroom are indicating improved student performance and better "on-task" behavior.
Research has demonstrated the importance of visual clues in language communication. This is of particular importance in a classroom setting and lighting may need to be evaluated along with any improved ceiling treatment for older classrooms. An interesting phenomenon that illustrates this point, known as the McGurk Effect can be demonstrated by dubbing a <ba> sound to a video of someone saying <ga>. The observer experiences the sound as <da>.