70V / 100V Line
Sum the taps (W) of the speakers on a constant-voltage line (70.7 V or 100 V), compute the total load, the equivalent impedance the amplifier sees, amplifier usage and headroom per the 80% rule. 100% in your browser.
Amplifier usage
Per-row breakdown
| Speaker | Tap | Qty | Load | % of total |
|---|
How it is calculated · 70V / 100V lines
1. On a constant-voltage line each speaker has a
transformer with taps in watts. The system load is the sum of the taps used:
load = Σ(tap × quantity).
2. The equivalent impedance the amplifier sees depends only on the
line voltage and the load: Z = V² / load. At 70.7 V,
V² = 5000; at 100 V, V² = 10000.
3. Amplifier usage: usage % = load / power × 100.
4. The 80 % rule: the safe limit is
power × margin. The headroom = limit − load leaves room for peaks,
cable loss and future speakers.
5. Verdict: OK if the load ≤ safe limit ·
tight if it exceeds the limit but fits the amp · overload
if the load exceeds the amplifier power.
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