Amplification isn’t usually an effective long-term strategy!

another thought

What about classroom audio distribution systems? Are they sufficient to mitigate poor acoustics?

Classroom audio distribution systems may be an excellent temporary solution where background noise problems are pending remedy, and may be useful for larger lecture halls to boost the signal source. However, there are drawbacks to such systems because they inhibit spontaneous interaction between students and teachers, which is a core learning activity.

Amplification also produces louder than conversational sound levels. And amplification systems are subject to failure, maintenance, and repair concerns. Amplification in one area also contributes to background noise in adjacent spaces, requiring additional mitigation.

What sound levels do teachers make? Assume no useful reflections and look at distance; they start at ~67dB at 1m/3.3ft., and the level falls off at 6dB per doubling of distance.  Note that useful reflections from a properly designed ceiling and walls can help focus the sound back to the listeners, improving the level at the listener by ~3dB. (2 diagrams in color for comparison (pressure plot?) (photo from Bob Coffeen) lecture ceilings)superimpose color plot and picture of poor and good design).

While sound systems do have benefits as mentioned earlier, there are issues that need to be considered beforehand:

1. Sound reinforcement makes the sound louder, and if the sound clarity was not acceptable due to high reverberation time beforehand, it will remain unclear, only louder.
2. If the background noise is too high, the amplified signal becomes too loud as well if you are trying to achieve an appropriate 15dB signal to noise ratio.  The classroom can become uncomfortable or noisy.

Additional concerns regarding relying on sound amplification:

1. The system reduces spontaneous interaction between the teacher and student- either students must pass a microphone to speak or may not be heard.
2. The system may employ wireless transmitters which require vigilance in regard to batteries.
3. An additional system that requires maintenance.

The minimum level of the teacher should be 50dBA at any place in the room, given a 35dBA background noise level.

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