70V/100V Distributed Speaker System Power Budget Calculator

Reference: DIST-70V-01. A different topology from anything else on this site — constant-voltage ("70-volt") distribution, used for paging, foyers, cry rooms, and other install-audio zones with a lot of low-power speakers on one amp channel, not a typical FOH rig. Each speaker gets a local step-down transformer set to a wattage tap rather than being wired directly, which sidesteps the impedance problem of paralleling many speakers on one channel. Because of that, sizing the system is just addition: total power drawn is the sum of every tap in use, and it has to stay under what the amplifier can deliver at that voltage.

System voltage 25V (some North American municipalities) 70V (70.7V, standard North America) 100V (Europe/UK) Amplifier's rated power at this voltage (W) — optional Speaker taps in use (W each), separated by commas or new lines Calculate

The line impedance figure above is informational — most amps in this application are power-rated at the voltage tap, not impedance-rated, so the power budget check is the one that actually matters. Every transformer in the chain has some insertion loss (more transformers, more loss), and transformers are prone to core saturation if driven too hard at low frequencies, which is a separate concern from the power budget and isn't checked here.

Source: Boyce, D. C. Live Sound Reinforcement, §11.7 "Transformer-Based Distributed Speaker Systems." Rewritten in Ryan's own words from the source material.