How speaker impedance adds up
Every loudspeaker presents a load to the amplifier, measured in ohms (Ω). When you connect more than one speaker to the same channel, the total load changes depending on the wiring. Amplifiers are designed for a minimum impedance – commonly 4 Ω or 8 Ω for home amplifiers and 1 – 2 Ω for car subwoofer amplifiers. Going below that minimum makes the amplifier deliver more current than it was built for.
Parallel: Z = Z₁ ÷ n · Series: Z = Z₁ × n · Series-parallel: Z = Z₁ (with 4 speakers)
Parallel wiring
All positive terminals connect together and all negative terminals connect together. The impedance drops: two 8 Ω speakers give 4 Ω, four give 2 Ω. Parallel wiring is the most common because each speaker works independently, but it quickly reaches loads that home amplifiers can't handle.
Series wiring
The positive of one speaker connects to the negative of the next. Impedances add up: two 8 Ω speakers become 16 Ω. The amplifier is safe, but it delivers less power and the speakers interact – a crossover designed for 8 Ω behaves differently, and if one speaker fails the whole chain goes silent.
Series-parallel wiring
With four speakers, wire two pairs in series and then connect the pairs in parallel. The total impedance equals one speaker's impedance – four 8 Ω speakers give 8 Ω. It's a good way to drive several speakers from a single channel without overloading it.
| Speakers | 8 Ω parallel | 8 Ω series | 4 Ω parallel | 4 Ω series |
|---|
| 2 | 4 Ω | 16 Ω | 2 Ω | 8 Ω |
| 3 | 2.67 Ω | 24 Ω | 1.33 Ω | 12 Ω |
| 4 | 2 Ω | 32 Ω | 1 Ω | 16 Ω |
Power and impedance
A solid-state amplifier behaves roughly like a voltage source: halving the impedance can nearly double the power it delivers, until it reaches its current limit. Amplifier specs list power at 8 Ω, 4 Ω and sometimes 2 Ω. OhmSum estimates output from the 8 Ω figure and divides the power between the speakers.
Dual voice coil subwoofers
Many car and home subwoofers have two voice coils (DVC). Each coil is treated like a separate speaker: a DVC 4 Ω sub can be wired to 2 Ω (parallel) or 8 Ω (series). With two DVC subs you have four coils, giving options of 1 Ω, 4 Ω or 16 Ω – pick the one closest to your amplifier's rated minimum.
Safer alternatives for many speakers
- Speaker selector with impedance protection for multiple rooms on one amplifier.
- Impedance-matching volume controls that use transformers to keep the load safe.
- 70 V / 100 V systems for offices, shops and restaurants with many ceiling speakers.
- Multi-channel amplifiers so each pair of speakers gets its own channel.
Frequently asked questions
What happens if I wire two 8 ohm speakers in parallel?
The load becomes 4 Ω. Most amplifiers handle this, but check the minimum impedance rating first.
Can I run four 8 ohm speakers on one channel?
Yes, wired series-parallel the load stays at 8 Ω. Wired in parallel it would be 2 Ω, which most home amplifiers can't drive safely.
Is series or parallel wiring better?
Parallel keeps speakers independent and delivers more power; series protects low-impedance-limited amplifiers but reduces power and can affect the sound.
What if the impedance is too low for my amplifier?
The amp may overheat, distort, go into protection or fail. Rewire for a higher impedance or use a separate amplifier channel.
How do I wire a dual voice coil subwoofer?
Treat each voice coil as a speaker. Parallel halves the coil impedance; series doubles it. Choose the result your amplifier supports.
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