Audio
70V/100V Line
Also called: constant voltage audio, 70 volt distributed audio, transformer tap
A distributed audio wiring scheme where amplifier output is stepped up to a constant voltage so dozens of speakers can share one long run, each drawing a set wattage via its transformer tap.
Constant-voltage distribution exists to solve distance and count. Low-impedance wiring gets impractical past a handful of speakers on a long run; stepping to 70V and tapping each speaker at 8, 16, or 32 watts lets one amplifier channel feed an entire floor over modest gauge cable. Restaurants, warehouses, retail, and paging systems are almost always built this way.
The design work is the tap budget: total tapped wattage must stay under the amplifier's rating with headroom, and taps should be set per zone loudness, not uniformly. We label taps at the speaker during install, because the alternative is a technician pulling tiles five years later trying to work out why one zone is quieter than the rest.
Related terms
- Ceiling Tile Speaker
- A loudspeaker installed into a suspended ceiling grid, used in distributed arrays so coverage is even across a room instead of loud at the front and thin at the back.
- Impedance
- The AC resistance a loudspeaker presents to an amplifier, measured in ohms; it determines how much power the amplifier delivers and how many speakers can safely share a channel.
- Sound Masking
- A system that emits precisely shaped background sound across a ceiling to raise the ambient noise floor, making nearby speech unintelligible and improving acoustic privacy.
More Audio terms
Support305 in the press
All press coverageNeed this specified correctly?
Our engineers will review your drawings or quote and tell you exactly where 70V/100V Line belongs in the design.
Talk to an engineer