Theaters, concert halls, churches, classrooms, and sound-proof rooms have to be designed and constructed so that their acoustic properties match their uses. In some spaces it is important that the speaker, singer, or musician or group be heard clearly in all parts of the room. A good concert hall has intimacy—music should sound as if it were being played in a small hall. It should have liveness and warmth—fullness of bass tones. The sound should be clear, and the audience should be able to locate the source of the sound. The sound should be uniform over the entire hall, and sounds from the stage should be blended by the time they are heard by the audience. Finally, the hall should be free of noise, from air handling systems as well as outside sounds.

In order to achieve these goals an acoustical engineer must consider not only the size and shape of the hall, but also the acoustic properties of materials used on the floors, ceilings, and walls of the room, as well as chairs and other objects in the room. Even the audience and air humidity affect the acoustic properties of the room! In general hard surfaces such as concrete, plaster, wood, and tile reflect sound while soft materials like carpet, heavy drapes, and plush upholstered chairs absorb sound. Room shapes and sizes that create standing waves should be avoided because sound at frequencies at which the standing waves occur will not be uniform. They will be loud in some places, soft in others.