An intercom, also called an intercommunication device, intercommunicator, or interphone, is a stand-alone voice communications system for use within a building, small collection of buildings or portably within a small coverage area, which functions independently of the public telephone network. Intercoms are generally mounted permanently in buildings and vehicles, but can also be detachable and portable. Intercoms can incorporate connections to public address loudspeaker systems, walkie talkies, telephones, and other intercom systems. Some intercom systems incorporate control of devices such as signal lights and door latches.
A butler uses an intercom on behalf of a lady.
An intercom control desk
Intercom used for team and driver communication in Formula One
Intercom system in the Pittock Mansion
A public address system is an electronic system comprising microphones, amplifiers, loudspeakers, and related equipment. It increases the apparent volume (loudness) of a human voice, musical instrument, or other acoustic sound source or recorded sound or music. PA systems are used in any public venue that requires that an announcer, performer, etc. be sufficiently audible at a distance or over a large area. Typical applications include sports stadiums, public transportation vehicles and facilities, and live or recorded music venues and events. A PA system may include multiple microphones or other sound sources, a mixing console to combine and modify multiple sources, and multiple amplifiers and loudspeakers for louder volume or wider distribution.
Rear panel of a medium-sized PA system, positioned at one side of the stage at a concert of the musical group Dead Can Dance in 2022, the size being about 3 m from left to right. The setup includes the mixing console for the sound engineer (operating interface with slide controls etc. on the rear) and also the power amplifiers with loudspeaker cables, not in the picture are only the loudspeaker systems distributed around the stage.
A late 19th-century speaking trumpet used by firefighters
A small sports megaphone for cheering at sporting events, next to a 3 in (8 cm) cigarette lighter for scale
Factory, February 1918, page 361