About the Speaker Impedance Calculator
This speaker wiring calculator works out the total impedance (ohm load) an amplifier sees when you connect several speakers together. Choose series, parallel or series-parallel wiring, enter the speakers' nominal impedances, and it returns the total load, whether it is safe for your amplifier's minimum rated impedance, and how the amplifier's power is shared between the speakers.
It is useful for guitar and bass players wiring extension cabinets or multi-speaker cabs (2×12, 4×12), car-audio builders wiring dual-voice-coil subwoofers, and anyone adding passive speakers to a home or PA amplifier. Running an amp below its minimum load can overheat it, while a load that is too high simply reduces output power.
Calculations use nominal impedance, the figure printed on the speaker or cabinet. Real speaker impedance varies with frequency, so treat the result as the nominal load that amplifier manufacturers specify against. Mismatched speakers can be combined, but they will not share power equally.
With the default inputs, the total impedance is 4 Ω. Change any value above to recalculate instantly.
How to use the speaker impedance calculator
- 1Choose the wiring: parallel, series or series-parallel.
- 2Enter each speaker's impedance (or the per-speaker value and layout for series-parallel).
- 3Enter the lowest load your amplifier is rated for.
- 4Check the total impedance and the amplifier verdict before connecting anything.
Formula and method
In series the same current flows through every speaker, so their impedances add. In parallel every speaker sees the same voltage and the currents add, so the reciprocals add; two identical speakers in parallel halve the impedance. Series-parallel wiring builds strings of S speakers in series and connects P strings in parallel, giving each string's impedance divided by the number of strings — which is why four 8 Ω speakers wired 2×2 stay at 8 Ω.
Power share follows the same physics: in series each speaker takes power in proportion to its impedance (P = I²Z); in parallel in proportion to 1/Z (P = V²/Z). Nominal impedances are used throughout.
- Z
- Total (nominal) impedance in ohms
- Zₛ
- Impedance of each identical speaker
- S
- Speakers in series in each string
- P
- Number of strings in parallel
Worked examples
Two 8 Ω cabinets in parallel
Two 8 Ω speakers in parallel: 1 ÷ (1/8 + 1/8) = 4 Ω, exactly the 4 Ω minimum of a typical solid-state amp, with power split 50/50.
Two 8 Ω speakers in series
In series the impedances add: 8 + 8 = 16 Ω. That is safe for any amp but a solid-state amp will deliver noticeably less power than into 4 Ω.
4×12 cab: four 8 Ω speakers wired 2×2
Each string of two 8 Ω speakers in series is 16 Ω; two strings in parallel halve that to 8 Ω, matching an 8 Ω amp output.
Mismatched speakers in parallel: 8, 8 and 4 Ω
1 ÷ (1/8 + 1/8 + 1/4) = 1 ÷ 0.5 = 2 Ω. The 4 Ω speaker draws half the power and each 8 Ω speaker a quarter.
Frequently asked questions
What happens when you wire two 8 ohm speakers in parallel?+
The total impedance halves to 4 Ω. Two 4 Ω speakers in parallel give 2 Ω and two 16 Ω speakers give 8 Ω. Always check that the amp is rated for the resulting load.
Is it bad to run speakers below the amp's rated impedance?+
Yes. A lower impedance draws more current, which can overheat a solid-state amplifier, trigger its protection or damage it. Tube amps should be connected to the output tap that matches the load exactly.
Can I mix speakers with different impedances?+
You can, and the formulas still give the correct total, but power will not be shared equally. In parallel the lower-impedance speaker gets more power; in series the higher-impedance speaker gets more.
How do I wire four speakers to keep the same impedance?+
Use series-parallel: wire two pairs in series and connect the pairs in parallel. Four 8 Ω speakers wired 2×2 present 8 Ω; four 16 Ω speakers present 16 Ω.
Does a higher impedance damage the amp?+
Not for solid-state amps — a higher load just reduces output power. Tube amps are less tolerant of large mismatches, so match the output tap to the cabinet whenever possible.