LOUDSPEAKERS IN CLASSROOMS

Herb Chaudiere

BRC Acoustics

Sound amplification is finding increased usage in classrooms to insure that all students can hear and understand what the instructor is saying. The instructor generally uses a wireless microphone to facilitate freedom of movement around the classroom. How the amplified sound is distributed to the listeners in the classroom is the single most critical element in the sound amplification system and is primarily a function of the selection and placement of the system loudspeakers.

There are a variety of types of loudspeakers that can be employed and a number of placements of the speakers that can be considered. A key characteristic of loudspeakers is the distribution pattern of the higher frequencies so essential to speech intelligibility. Another important characteristic is the ability to direct the sound uniformly to the intended listeners while minimizing sound directed towards sound reflective surfaces or areas where there are no listeners. And finally a loudspeaker should sound natural; it should reproduce sound with reasonable fidelity, especially if the sound system will also be used for multi-media sound reproduction.

Ideally the amplified sound should come from the same directions as the natural sound of the talker. When sound comes from several directions, from speakers that are at different distances from the listener, there will be confusion and degradation of the sound quality due to interference effects between the sound coming from the various speakers. However, in a typical classroom situation the instructor needs the freedom of mobility and to be heard equally well, regardless of where they are in the room. So, directional realism is traded off for flexibility.

The best, but not necessarily the most cost effective, system is one utilizing individual ceiling mounted speakers, distributed uniformly throughout the room. Most classrooms do not have high enough ceilings to effectively utilize wall-mounted speakers to provide uniform sound coverage throughout the room. More cost effective, particularly in a retrofit situation, is a centrally located ceiling speaker assembly, which can provide very good uniformity of sound coverage throughout the room.

Speaker type and location are the most critical elements that determine the speech intelligibility of a classroom amplification system. If the acoustical characteristics of the room are known, computer programs are available that can accurately predict speech intelligibility, as well as sound distribution, for selected loudspeakers. If acoustical data is lacking and cost is a concern, the centrally located ceiling speaker assembly is the best choice to distribute sound effectively and enhance speech intelligibility.