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Speaker Impedance Calculator
Work out the total impedance of 2 to 8 speakers wired in series, in parallel or in a series-parallel combination. Check it against your amplifier's minimum load, see how the power splits between speakers and follow the generated wiring diagram.
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Set every speaker to
Total impedance–
Wiring diagram
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How to use the Speaker Impedance Calculator
- Choose the wiring: Series, Parallel or Series-parallel.
- Set the number of speakers (or the strings/groups for series-parallel) and enter each speaker's nominal impedance, or tap a value to set them all.
- Pick your amplifier's minimum load and, optionally, its rated power to see the estimated power per speaker.
- Read the total impedance and the compatibility verdict, with the formula worked out.
- Follow the wiring diagram and the numbered steps, keeping + to + throughout. Download the diagram if you want it on hand.
Speaker impedance formulas
- Series: Ztotal = Z1 + Z2 + … + Zn. The same current flows through every speaker.
- Parallel: Ztotal = 1 ÷ (1/Z1 + 1/Z2 + … + 1/Zn). Every speaker gets the same voltage. For identical speakers, Ztotal = Z ÷ n.
- Series strings in parallel: add up each string, then combine the strings with the parallel formula.
- Parallel groups in series: work out each parallel group, then add the groups together.
Example: four 8 Ω speakers as two series strings give 16 Ω per string, and two 16 Ω strings in parallel give 8 Ω, so a 4 Ω-minimum amplifier is comfortably within its rating.
Common speaker wiring combinations
| Speakers | Series | Parallel | Series-parallel |
|---|---|---|---|
| 2 × 4 Ω | 8 Ω | 2 Ω | – |
| 2 × 8 Ω | 16 Ω | 4 Ω | – |
| 3 × 8 Ω | 24 Ω | 2.67 Ω | – |
| 4 × 4 Ω | 16 Ω | 1 Ω | 4 Ω (2 strings of 2) |
| 4 × 8 Ω | 32 Ω | 2 Ω | 8 Ω (2 strings of 2) |
| 6 × 8 Ω | 48 Ω | 1.33 Ω | 12 Ω (2 strings of 3) or 5.33 Ω (3 strings of 2) |
| 8 × 8 Ω | 64 Ω | 1 Ω | 16 Ω (2 strings of 4) or 4 Ω (4 strings of 2) |
Wiring tips
- Polarity matters. Keep + to + and − to − (red to red, black to black). A reversed speaker moves out of phase and cancels bass.
- Dual voice coil subwoofers count as two "speakers" per driver: wire the two coils in series or parallel first, then combine the drivers.
- Bridged amplifiers usually need a higher minimum load than a single channel (often double). Check the manual before bridging into a low impedance.
- 70 V and 100 V distributed systems used for background music in shops and offices work differently, using transformer taps instead of ohms. This calculator is for ordinary low-impedance speakers.
- Use heavy enough wire for long runs into low impedances, because wire resistance eats more power when the load is small.
Frequently asked questions
How do you calculate speaker impedance in parallel?
Add the reciprocals of each impedance and take the reciprocal of the sum: Z = 1 / (1/Z1 + 1/Z2 + ...). For identical speakers this is simply the impedance divided by the number of speakers, so two 8 ohm speakers in parallel give 4 ohms and four give 2 ohms.
How do you calculate speaker impedance in series?
Add the impedances together: Z = Z1 + Z2 + ... Two 8 ohm speakers in series make 16 ohms, and two 4 ohm speakers make 8 ohms.
What is series-parallel speaker wiring?
It combines both methods so the total stays close to the impedance of one speaker. With four 8 ohm speakers, two series pairs (16 ohms each) wired in parallel give 8 ohms. With identical speakers, parallel groups wired in series give the same total.
What happens if the impedance is too low for my amplifier?
A load below the amplifier's minimum rating makes it draw more current than it was designed for. It may run hot, distort, go into protection or eventually fail. Keep the total at or above the lowest impedance the amp is rated for, per channel or in bridged mode as specified in its manual.
Is it safe to use a higher impedance than the amplifier is rated for?
Yes. A higher impedance is easy on the amplifier, but it delivers less power. For example, an amp rated 100 W at 8 ohms gives roughly 50 W into 16 ohms.
Can I mix speakers with different impedances?
You can, and the calculator handles it, but the power will not split evenly. In parallel the lower-impedance speaker takes more power; in series the higher-impedance speaker does. The power table shows the share each speaker receives.
Is the nominal impedance the real impedance?
No. A speaker's impedance changes with frequency, and the nominal rating (4, 6 or 8 ohms) is a simplified figure. Real impedance often dips below the nominal value at some frequencies, which is why it is wise not to push an amplifier hard at its minimum load.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.
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