Room acoustics and background noise

There is an excellent web page that illustrates both with sight (waveforms) and sound clips how increasing the reverberation time (0, 0.8, 1.3, and 2.0 seconds) makes speech less intelligible. Another page on the same site has two more sound clips of the same speech sample with both a shorter reverberation time of 0.6 seconds and a longer one of 5.0 seconds.

Background noise is another factor that affects how clearly a speaker is heard. A room might sound fine until the heating or air conditioning system starts running. To avoid an unpleasant surprise, a speaker should plan ahead to watch and listen to the room for long enough to find out what the ventilation does.

Effects of reverberation time (RT) and background noise are discussed at length in an publication by the Acoustical Society of America about Classroom Acoustics. There also is an American National Standard for Acoustic Performance Criteria, Design Requirements, and Guidelines for Schools, which is summarized here. Jonathan Sheaffer has discussed the Prediction and Evaluation of RT Design Criteria. He plots suggested times both from an acoustics handbook and two European standards.