Mixing 4-ohm and 8-ohm speakers on the same amplifier is a common question, especially when adding speakers or a passive subwoofer. It can be done, but you need to understand what happens to the load on your amplifier.
- On separate channels (e.g. 8-ohm left/right, 4-ohm centre on its own channel), mixing is generally fine if each channel supports the speaker’s impedance.
- On the same channel, impedances combine. In parallel, 4 + 8 ohms makes about 2.7 ohms, which many amps can’t handle.
- Powered subwoofers have their own amp, so impedance doesn’t matter for them.
What impedance means
Impedance (in ohms) is roughly how much a speaker resists the current from the amplifier. Lower impedance draws more current. Amplifiers are designed for a minimum load; going below it can cause overheating, protection shutdowns or damage.
The parallel impedance maths
When two speakers are wired in parallel on one channel, the combined load is (R1 × R2) ÷ (R1 + R2).
| Speakers in parallel | Combined load |
|---|---|
| 8 Ω + 8 Ω | 4 Ω |
| 4 Ω + 8 Ω | ≈ 2.7 Ω |
| 4 Ω + 4 Ω | 2 Ω |
In series, impedances add (4 + 8 = 12 ohms), which is safe for the amp but means less power and the two speakers won’t share power evenly. You can try the numbers in the impedance tool on our subwoofer calculator.
What about powered subwoofers?
A powered (active) sub has its own matched amplifier, so its driver’s impedance doesn’t affect your receiver at all. Even when connected through speaker-level inputs, a powered sub presents a very high, harmless load. See passive vs active subwoofers.
When mixing impedances is safe
- Each speaker is on its own amplifier channel and that channel is rated for the speaker’s impedance.
- Your receiver is rated for 4-ohm loads (check the manual or rear panel) if any speaker is 4 ohms.
- In car audio, dual-voice-coil subs are wired to reach a final load the amp is stable at. See car subwoofer wiring basics.
Practical advice
Don’t parallel speakers on one receiver channel unless you’re sure the amp can handle the combined load. If you’re adding bass, a powered subwoofer sidesteps the issue entirely.