Wiring two or more speakers to a single amplifier channel changes the total electrical load the amp sees. Get it wrong and you risk damaging your amplifier, under-driving a driver, or blowing a tweeter with mismatched power. This speaker impedance calculator works out the combined load for any wiring topology — series, parallel, or mixed series-parallel — and checks whether the result is safe for your amplifier.
How the formulas work
Every speaker has a nominal impedance expressed in ohms (Ω). When you connect speakers together, the total load depends on the wiring arrangement.
Series wiring
Drivers connected end-to-end share the same current. Impedances simply add:
Z_total = Z₁ + Z₂ + Z₃ + …
Two 8 Ω woofers in series give 16 Ω. The amplifier sees a higher load, which is safer but means less current flows, so each driver receives less power for a given amplifier output voltage. Series wiring is common in vintage guitar cabinets (two 8 Ω drivers → 16 Ω for a valve amp that prefers high loads).
Parallel wiring
Drivers connected across the same two terminals share the same voltage. You add the reciprocals of the impedances:
1/Z_total = 1/Z₁ + 1/Z₂ + 1/Z₃ + …
Two 8 Ω woofers in parallel give 4 Ω. A modern solid-state amplifier comfortable with 4 Ω loads will drive this combination safely and each driver receives half the total power. This is the most popular configuration in home theatre subwoofer cabinets and PA cabs.
Mixed series-parallel
A 4 × 8 Ω cabinet typically wires the drivers as two series pairs (8 + 8 = 16 Ω per pair) connected in parallel (16 ∥ 16 = 8 Ω total). The calculator lets you define speaker groups with their own wiring, then combine the groups at the top level — reflecting exactly that kind of real-world cabinet design.
Power distribution
Power does not split evenly unless all impedances match. In a parallel circuit every driver sees the same voltage, so the driver with the lower impedance draws more current and receives more power. In a series circuit every driver carries the same current, so the driver with the higher impedance dissipates more power (P = I²·Z). The calculator derives the exact fraction for each driver and flags any over-power risk against the rated RMS figure you enter.
Worked example
A DIY subwoofer cabinet contains four 4 Ω drivers rated 200 W RMS each. Two pairs are wired in series (4 + 4 = 8 Ω per pair) and the two pairs are then combined in parallel (8 ∥ 8 = 4 Ω total). Total system power handling = 200 W (the series limit of each pair) × 2 pairs = 400 W RMS. A 4 Ω-rated 500 W amplifier driving this cabinet will operate well within its rated load and deliver up to 400 W before any driver’s thermal limit is reached.
| Topology | Two × 4 Ω | Two × 8 Ω | Four × 8 Ω (2S2P) |
|---|---|---|---|
| Series | 8 Ω | 16 Ω | 16 Ω |
| Parallel | 2 Ω | 4 Ω | 2 Ω |
| Series then parallel | — | — | 4 Ω |
Formula note
Impedance in this calculator is treated as a real (resistive) scalar — the nominal figure from the driver’s datasheet. Real loudspeaker impedance is frequency-dependent and complex (resistive + reactive). For crossover design or amplifier stability analysis, use measured impedance sweeps (e.g. via REW or LTspice). For cabinet wiring and amplifier-load purposes, the nominal value gives the right answer for all practical day-to-day calculations.