The science of sound as it pertains to buildings. There are three major branches of architectural acoustics. (1) Room acoustics involves the design of the interior of buildings to project reflected and diffused sound at appropriate levels and time intervals and with appropriate esthetic qualities for music and adequate intelligibility for speech. Room acoustics is an essential component of the design of theaters, concert halls, lecture rooms, classrooms, and churches, among other building types. (2) Noise control or noise management involves the reduction and control of noise between a potentially disturbing sound source and a listener. The walls, floors, ceilings, windows, and doors in buildings reduce sound energy as it travels through them. Sources of disturbing noise may be equipment and people within the building or intruding noise from external sources of sound, such as amplified music, airplanes, or highways. Noise from building services, including heating, ventilating, and air-conditioning systems; lighting systems; communication, voice, and data systems; and electric power systems, must also be controlled so that it does not disturb people using the buildings. (3) The design of sound reinforcement and enhancement systems uses electronic equipment to improve the quality of the sounds heard in rooms.