A public address system (PA system) is an electronic sound amplification and distribution system with a microphone, amplifier and loudspeakers, used to allow a person to address a large public, for example for announcements of movements at large and noisy air and rail terminals or at a sports stadium. The term is also used for systems which may additionally have a mixing console, and amplifiers and loudspeakers suitable for music as well as speech, used to reinforce a sound source, such as recorded music or a person giving a speech or distributing the sound throughout a venue or building. The loudspeaker is used to convert electrical signals into sound.The primary input sources are microphones for live announcements and a source of recorded sound. There may be a system which allows operators, or automated equipment, to select from a number of standard prerecorded messages.
PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings and locations. Intercom systems, installed in many buildings, have microphones in many rooms allowing the occupants to respond to announcements.
The simplest PA systems consist of a microphone, an amplifier, and one or more loudspeakers. Simple and small PA systems of this type are often used in small venues such as school auditoriums, religious occasions and festivals, small gatherings and meetings. A sound source such as a compact disc player or radio may be connected to a PA system so that music can be played through the system.Small clubs and party halls use a fairly simple set-up, with large Front of House speakers and subwoofers aimed at the audience, and smaller monitor speakers aimed back at the performers so that they can hear their vocals and instruments.
Large PA systems which have speakers that cover an entire campus of a college or an industrial site, or an entire outdoor complex (e.g., an athletic stadium). This type of PA system may also be used as an alert system during an emergency.This type of PA systems are popular in music concerts and huge stage gatherings, a more powerful and more complicated PA System is used to provide live sound reproduction.
All PA systems have a potential for audio feedback, which occurs when sound from the speakers is picked up by the microphone and is then re-amplified and sent through the speakers again. It often sounds like a loud high-pitched squeal or screech, and can occur when the volume of the system is turned up too high.