A public address system (PA system) is a sound amplification system used to allow a person or persons to address an audience at a greater volume than would be possible or practicable without such a system. At a minimum, such a system comprises a microphone, an amplifier and a loudspeaker. Examples of content include announcements and other audio material at sports stadiums, air and rail terminals, and the sound produced by a singer, musician or musical ensemble, as well as recorded music. A PA system may include multiple microphones and/or other sound sources, a mixing console to combine and modify multiple sources, and multiple amplifiers and loudspeakers for louder volume, greater coverage and/or wider distribution, such as that required to provide sound throughout an entertainment venue, an office building or retail space, or an outdoor environment.
Simple PA systems are often used in small venues such as school auditoriums, churches, and small bars. PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings and locations, such as schools, stadiums and large passenger vessels and aircraft. Intercom systems, installed in many buildings, have both speakers throughout a building, and microphones in many rooms allowing the occupants to respond to announcements.
Sound reinforcement systems and PA systems may use some similar components, but with differing application, although the distinction between the two terms is not clear-cut. Sound reinforcement systems are for live music or performance, whereas PA systems are primarily for reproduction of speech. In Britain any PA system is sometimes colloquially referred to as a Tannoy, after the company of that name now owned by TC Electronic Group, which supplied a great many of the PA systems used previously in Britain.