70-Volt Distributed Speaker Line
Tap-wattage budget, reflected line impedance (Z = V^2/P), remaining taps.
Example
You enter
- Amplifier rated power (W) 200
- Headroom (%) 20
- Watts per tap (W) 8
- Number of taps 16
- Line voltage 70.7
You get
- Total tap w 128
- Budget limit w 160
- Reflected impedance 39.05
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method.
Details, formula, and sources
ScopeTap-wattage budget, reflected line impedance (Z = V^2/P), remaining taps, and run line-loss for a constant-voltage 70 V / 100 V audio line (NEC 640 / 725).
Formula or tableConstant-voltage line: total tap load = sum of tap watts; budget verdict total <= rating*(1 - headroom); reflected impedance Z = V^2 / P_total; line loss from wire resistance and the line current I = P_total/V.
Source and editionConstant-voltage (70 V / 100 V) distributed-audio line design - tap-wattage budget, reflected line impedance Z = V^2/P, and run line-loss - per the standard 70 V distributed-system practice and NEC Article 640 / 725 (Class 2/3 audio) wiring, by name; first-principles Ohm's law.
Free accessFirst-principles Ohm's law. The amplifier spec governs the rated power and minimum load.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namesamp_rated_w, headroom_percent, tap_watts, tap_count, line_voltage_v, total_tap_w, budget_limit_w, reflected_impedance_ohm
- Tap settings the speaker tap wattages are read off the transformer taps; user-suppliedloudspeaker tap chart