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Collaboration, Voice & AV · Intermediate

Constant-Voltage Audio Distribution

A loudspeaker system using 70 V or 100 V lines with transformer taps so many speakers can share one amplifier channel.

Definition

In a constant-voltage system, each loudspeaker's transformer tap sets its power draw, and the total of all taps must not exceed the amplifier's rating, typically with about 20 percent headroom. High line voltage reduces current and cable losses over long runs. It is common for paging and background music; 70 V is typical in North America and 100 V in Europe.

Example

Thirty ceiling speakers tapped at 2 W (60 W total) run from a 100 W amplifier on a 70 V line.

Exam tip

Add tap wattages and leave headroom; impedance math is not needed for constant-voltage systems.

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