The effect of long reverberation times (echos) on the ability to understand speech in classrooms

As you may have noticed, in certain classrooms, and more often in multipurpose rooms, planning committees often choose easy-to-clean surfaces like epoxy-coated concrete block for walls, and simple paint on the underside of the metal roof deck.

While very practical from that standpoint, these spaces can make understanding speech a real chore. You can see the presenter's mouth moving, but you have a dickens of a time understanding the words. Syllables all run together into a mumbling mess. Music often sounds great, because of the same blending that makes speech impossible.

Sometimes, planning committees also direct an architect to make the space "usable without having to talk into a microphone." Given that direction, the architect tries to keep the walls and ceilng "hard" and add acoustic treatment only over the audience.

This is partially effective IF the room is always used with the presenter's position always at the same side of the room.

As the sample illustration below shows, it is possible for an acoustic consultant to demonstrate the effect of more or less acoustic treatment within a planned room. The website of McSquared System Design Group provides both graphs and actual sound clips of speech when the reverberation time (and thus the amount of acoustic treatment) is varied for a 40ftx40ftx10ft classroom.

One sample from their site:

There is much more information at their site. This is good stuff! While you're there, look at the many other pages which deal with acoustic problems.

Click here to go to the site.

Have a question about classroom design, or a good idea? E-mail: is listed by the National Clearing House for Educational Facilities (NCEF)