A public address (PA) system is an electronic amplification system with a mixer, amplifier and loudspeakers, used to reinforce a given sound, e.g., a person making a speech, a DJ playing prerecorded music, and distributing the sound throughout a venue or building.

Simple PA systems are often used in small venues such as school auditoriums, churches, and small bars. PA systems with a larger number of speakers are widely used in institutional and commercial buildings, to read announcements or declare states of emergency. Intercom systems, which are often used in schools, also have two way speakers in each room so that the occupants can reply to the central office.

Small public address systems

The simplest PA systems consist of a microphone, a modestly-powered mixer-amplifier (which incorporates a mixer and an amplifier in a single cabinet) and one or more loudspeakers. Simple PA systems of this type, often providing 50 to 200 watts of power, are often used in small venues such as school auditoriums, churches, and small bars. A sound source such as a CD player or radio may be connected to a PA system so that music can be played through the system.

Public address systems typically consist of input sources, preamplifiers and/or signal routers, amplifiers, control and monitoring equipment, and loudspeakers. Input sources refer to the microphones and CD Players that provide a sound input for the system. These input sources are fed into the preamplifiers and signal routers that determine the zones to which the audio signal is fed. The pre-amplified signals are then passed into the amplifiers. These amplifiers will amplify the audio signals to 25V, 70V or 100V speaker line level. Control equipment monitors the amplifiers and speaker lines for faults before it reaches the loudspeakers.

Large public address systems

Some PA systems have speakers that cover an entire campus of a college or industrial site, or an entire outdoor complex (e.g., an athletic stadium). These systems can be devided to multiple zones and also have additional functions. The Larger systems such as Bogen Multicom 2000 and Multicom Quantum can provide loud paging from hundreds to thousands of speakers. In addition they provide telephone functionality, timed tones, and clock synchronization.

Telephone paging systems

Most modern telephone systems, such as PBX and VOIP, use a paging system that acts as a liaison between the telephone and a PA amplifier. In key telephone systems such as those by Mitel, NEC, Nortel, Toshiba, Avaya or Alcatel-Lucent, paging equipment is usually built into the telephone system itself, and allows announcements to be paged over the phone speakers themselves, through external speakers or through both external and internal telephone speakers.

In PBX and larger VOIP telephone systems such as those by Mitel, NEC, Nortel, Cisco, Avaya, Siemens or Alcatel-Lucent, used for larger enterprise applications, paging equipment may not be built into the telephone system. Instead the system provider must provide a separate paging controller connected to a trunk port on the actual telephone system. The paging controller is accessed as either an unused directory number or unused central office line. Access to the paging system is provided through a “trunk access” code or a pre-programmed feature button on the telephone set itself.

Many retailers and offices choose to use the telephone system as the sole access point for the paging system, because the equipment is already “paging system”-ready. One disadvantage of telephone paging systems compared to microphone paging systems is that the noise associated with hanging up the telephone can be heard over the speakers.

PA Over IP

“PA over IP” refers to PA paging and intercom systems that use an Ethernet or GSM-R network instead of a centralized analog or DSP amplifier to distribute the paging to all of the locations in a building or company. Distributed network attached amplifiers and intercom units are used to provide the communication function. At the transmission end, a computer with specialized software broadcasts the audio data digitally over the local area network, using audio from the computer’s sound card inputs or from stored audio files. At the receiving end, specialized intercom modules receive these network transmissions and reproduce the analog audio signal. These are small specialized network appliances with an IP address just like any other computer on the network.

Such systems are connected using standard networking infrastructure and thus allow more flexible configurations than those possible using traditional analog PA wiring. For example, a user can have multiple remote sites tied together through the local area network (LAN) and through the internet so that one location can be used to send audio signals to any or all of these locations. Use of the internet allows PA systems to span multiple buildings, and allows for long-range PA receivers in satellite locations. Bogen Quantum provides for a distributed processing for multiple or relocatable transmission (control) stations on a local, wide or area networks.