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a party-line system, all of the people on a given channel can
talk and listen to each other simultaneously. Each intercom
station or beltpack has its own mic preamp and speaker/headphone
amplifier circuitry‹known as a distributed-amplifier system.
Headsets or gooseneck mics and integral station speakers are
used to talk and listen. A standard two-conductor shielded microphone
cable, with 3-pin XLR connectors, is used for each channel of
communication. One conductor carries the full-duplex (two-way)
audio among the connected intercom stations, one carries the
30 volts DC current that powers those stations, and the shield
acts as the ground. Every system/installation requires at least
one power supply to provide the necessary DC current.
One or
more channels may be used in an installation or to coordinate
an event. All the technical staff running a high school play
or small community theatre may talk together on one channel,
while a larger production might have separate channels for
stage manager, spot lights, props, audio, and so on. The director
will typically have a multi-channel intercom station allowing
communications with people on any or all of the various channels.
Party-line
intercom systems are widely used in live theatre, live performance,
performance lighting, and auditoriums/stadiums/facilities
that host live events. They are also found in small to mid-sized
TV/broadcast studios, smaller broadcast production trucks,
industrial settings, simulation and medical theatre applications,
and so on.
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