1. The study of sound and sound waves.

2. The characteristics of a building, especially an auditorium, with regard to its ability to enable speech and music to be heard clearly within it. For this purpose there should be no obtrusive echoes or resonances and the reverberation time should be near the optimum for the hall. Echoes are reduced by avoiding sweeping curved surfaces that could focus the sound and by breaking up large plane surfaces or covering them with sound-absorbing materials. Resonance is avoided by avoiding simple ratios for the main dimensions of the room, so that no one wavelength of sound is a factor of more than one of them. If the reverberation time is too long, speech will sound indistinct and music will be badly articulated, with one note persisting during the next. However, if it is too short, music sounds dead. Reverberation time is long in a bare room with hard walls and can be deliberately reduced by carpets, soft furnishings, and sound-absorbent (‘acoustic’) felt. Reverberation times tend to be reduced by the presence of an audience, and this must be taken into account in the design of the building.

http://acousticalsociety.org/ The website of the Acoustical Society of America

http://www.ioa.org.uk/ The website of the UK Institute of Acoustics