Speaker Impedance (4Ω vs 8Ω)
Speaker impedance is the electrical resistance a speaker presents to the amplifier, measured in ohms (Ω). Typical values are 4Ω, 6Ω, or 8Ω. Lower impedance draws more current from the amp, giving more power output but requiring an amp that can handle the load.
Speaker impedance is the electrical resistance a speaker presents to the amplifier, measured in ohms (Ω). Nominal ratings are typically 4Ω, 6Ω, or 8Ω, but real speakers have impedance that varies with frequency (often dipping much lower at bass frequencies).
Why it matters
Amps deliver more power into lower-impedance loads. A TPA3255 amp rated for “150W at 4Ω” typically delivers about “75W at 8Ω” — the impedance halves the power output.
Amp compatibility rules
- 4Ω speakers — need an amp rated to drive 4Ω loads cleanly. Not all amps can.
- 8Ω speakers — will work with any amp but you get less power
- Real-world impedance dips below 4Ω (some to 2Ω) at bass frequencies can stress the amp
What to check on your speakers
Look for the impedance rating on the back of the speaker or in the specs. If it says “4 ohm nominal, dips to 3 ohm” that means real impedance goes below 4Ω — you need an amp that’s comfortable at 4Ω or lower.
Budget-hi-fi impedance realities
Most bookshelf speakers in our catalog are 4-6Ω nominal: Klipsch RP-500M II, HiVi-Swans D3.1 MKII. Modern TPA3255 amps handle these easily.
Common myths & realities
8-ohm speakers always work with 4-ohm amps
True, but you get less power. And a 4-ohm speaker on an amp not rated for 4 ohms can overheat.
Ready to see this in action?
Browse honest, hands-on reviews of budget hi-fi gear that puts these concepts to the test.
