Read the circuit
before you run the cable
Start with the channel and the connection scheme. Then size the cable for that load and route. Keep the equipment manual alongside the printed plan.
01 / Get the right numbers first
Write down each speaker’s nominal impedance, the amplifier’s permitted speaker load for the output you intend to use, and the actual cable route. Record the model numbers beside those values. A specification attached to a different output mode is not a substitute. For example, Yamaha’s RX-A4A instructions set different speaker requirements for its front channels and its other channels. That example illustrates why the exact manual matters; those limits are not defaults for other amplifiers. Yamaha speaker requirements.
Count speakers on one amplifier channel. A normal left speaker on the left channel and right speaker on the right channel is a one-speaker calculation repeated twice. Selecting “2 speakers” here describes two speakers connected to the same channel. Do not join the left and right outputs to turn this drawing into a mono system.
If a specification gives a range or you cannot identify the minimum permitted load, keep that question unresolved and consult the manufacturer. The initial 4 Ω value is just an example. Substituting it for an unknown specification would make the comparison look more definite than your information allows.
02 / What nominal impedance can tell you
A speaker’s nominal impedance is a useful classification, not a constant resistance throughout the audio range. The actual impedance varies with frequency, and a manufacturer may separately state a minimum. Focal explains this distinction in its speaker impedance guidance. This tool substitutes the nominal values into a resistive circuit model. It does not model the impedance curve, electrical phase, or amplifier behavior.
A calculated load below the minimum you entered is a reason to reject that plan against that specification. An equal or higher result only clears that numerical comparison. It does not check the amplifier’s current or thermal limits, the speakers’ power handling, or operation at your listening level. Cable resistance is deliberately not added to the nominal load comparison: do not use a lossy cable to “fix” an unsuitable speaker arrangement.
03 / Follow series and parallel connections
In a series chain, the same current passes through each speaker. Add the nominal values: Z = Z₁ + Z₂ + …. In parallel, each branch spans the same pair of nodes; add reciprocals: 1/Z = 1/Z₁ + 1/Z₂ + …. The parallel equivalent is below the smallest individual resistance. These are the standard series and parallel circuit relationships.
For the four-speaker series-parallel option here, speakers 1 and 2 make the first series pair and speakers 3 and 4 make the second. The two pairs then connect in parallel. Let A = Z₁ + Z₂ and B = Z₃ + Z₄; the combined value is AB / (A + B). This grouping is shown explicitly in the diagram. A different pairing can change the result when the speaker values differ.
Fender’s wiring explanation confirms the familiar examples: two 8 Ω speakers give 16 Ω in series or 4 Ω in parallel, while two series pairs of 8 Ω speakers give 8 Ω overall. Those examples validate the arithmetic; they do not prescribe a home-audio installation.
Series wiring is not a universal workaround for low parallel impedance. QSC explains how frequency-dependent speaker impedances can cause unequal voltage sharing and alter frequency response in series-connected speakers. QSC on series versus parallel surrounds. Use the series options to understand or document a supported design, not to assume any combination of speakers will behave identically.
04 / Work through two connection examples
Two speakers on the same channel
With two nominal 8 Ω speakers in parallel, 1/Z = 1/8 + 1/8 = 1/4, so Z = 4 Ω. Against an entered 4 Ω minimum, the result is “equal.” Change either the amplifier specification or one speaker and recalculate. Putting both speakers in series instead gives 16 Ω; this change also changes the circuit, so retain the matching diagram.
Four speakers with unequal labels
Enter 4, 8, 6 and 6 Ω in that order and choose two series pairs in parallel. Pair 1 is 12 Ω and pair 2 is 12 Ω, giving 6 Ω overall. If you enter 4, 6, 8 and 6 instead, the pairs become 10 and 14 Ω, giving 140/24 ≈ 5.83 Ω. A list of four values alone is not a wiring plan; the grouping matters.
These are illustrative calculations, not recommendations for those combinations. The output describes nominal electrical load and does not assign wattage to individual speakers.
05 / Measure the cable that the model describes
The cable estimate represents one shared two-conductor feeder between an amplifier channel and the complete speaker group. Enter its one-way route length. Ten metres of cable contains a ten-metre outgoing conductor and a ten-metre return conductor; the resistance calculation therefore uses twenty metres of conductor. Switching metres and feet converts the current distance instead of reinterpreting the same number.
The short connections within the group are idealized as zero resistance. If the speakers are distributed around a room with substantial cable between them, that simplification can understate loss. Separate cables returning to the amplifier have separate branch currents and must be assessed as their own circuits. Do not enter the sum of all room cables as one shared length and treat the result as an installation design.
For a uniform conductor, resistance is resistivity multiplied by length, divided by conductor area. Thus the feeder loop uses Rloop = 2Lρ/A, where L is metres one way and A is mm². OpenStax resistance and resistivity. The copper constant here is ρ = 0.017241 Ω·mm²/m at 20 °C from NBS Handbook 100. Actual construction and temperature can change resistance, so use a cable manufacturer’s measured specification when precision matters.
06 / Three losses with different meanings
The model treats the cable loop and speaker group as two series resistances. Using resistive power P = I²R, the cable’s share of the power entering that combined circuit is 100 × Rloop / (Z + Rloop). This is the “cable heat loss” used by the selectable target. The power relationship is described in OpenStax electrical energy and power.
The speaker voltage fraction is Z / (Z + Rloop). At a fixed amplifier voltage, the speaker power relative to a zero-resistance cable is the square of that fraction. “Speaker power reduction” is 100 times one minus that squared fraction. Level attenuation is −20 log₁₀ of the voltage fraction, shown as a positive loss in dB. These are derived circuit results, not listening-test findings.
Why 5% does not mean the same thing everywhere
Imagine a 1 Ω cable loop feeding a resistive 4 Ω load. The cable dissipates 1/5 = 20% of the power entering the circuit. The speaker receives 4/5 of the voltage, so its power is 16/25 = 64% of the zero-cable-resistance case: a 36% reduction. Comparing those percentages without their denominators would produce conflicting answers from the same circuit.
Choose 1%, 3%, 5% or 10% as your own heat-loss comparison target. These settings are not universal audibility thresholds, installation ratings or safety limits. A size that meets the target only meets this particular calculation.
07 / Copper size reference
Lower AWG numbers indicate larger conductors. The areas below are rounded reference values, not the outside diameter of the insulated cable. The resistance column covers one conductor; double the route length before using it for a two-conductor loop. Values use the same 20 °C standard-copper model as the planner.
| AWG | Area (mm²) | Ω / 1,000 m | Ω / 1,000 ft |
|---|---|---|---|
| 18 | 0.823 | 20.95 | 6.39 |
| 16 | 1.310 | 13.16 | 4.01 |
| 14 | 2.080 | 8.29 | 2.53 |
| 12 | 3.310 | 5.21 | 1.59 |
| 10 | 5.261 | 3.28 | 1.00 |
For example, 14 AWG has about 2.08 mm² of conductor area in this table. A 10 m run gives a 0.16578 Ω loop. With a nominal 4 Ω group, the calculated cable heat loss is approximately 3.98%; it meets the illustrative 5% target. Reducing the target to 3% changes which sizes qualify.
Metric sizes are calculated from their stated areas, rather than rounded into an AWG equivalent. The table does not estimate copper-clad aluminium cable, connector resistance, or current capacity. “Smallest listed conductor” means the smallest area among the options that meets the selected target; confirm that your terminals accept the chosen cable.
08 / Take a complete plan to the equipment
Print the current result or use your browser’s save-to-PDF destination. It includes the speaker labels, connection drawing, amplifier comparison, selected cable, loss estimates and assumptions. Add the actual equipment model numbers, intended channel and cable route to your copy. If you change a topology or move a speaker between pairs, print an updated diagram.
Before connecting, use the equipment’s own connection instructions and power-down procedure. The schematic explains electrical connections; it is not a view of your amplifier’s terminals. This planner does not cover bridged outputs, transformer/tube-output matching, 70/100 V distribution, active speakers or impedance-matching selectors. Those arrangements need their own documentation and calculations.
Continue with our speaker wiring guide for the surrounding setup task. If your question is where speakers should go rather than how their loads combine, read the separate speaker placement calculator guide. Positioning and wiring answer different questions, and neither should be inferred from the other’s diagram.