Speaker impedance is the spec most people skip, and it's the one that can make a receiver overheat or shut itself off. Here's what the ohms rating actually means, how to match speakers to an amp, and the wiring mistake that catches people adding a second pair of speakers.
Impedance (in ohms) is how much a speaker resists current. Lower impedance means the speaker draws more current from the amplifier. Home speakers are usually rated 4, 6, or 8 ohms.
Make sure your speakers' impedance is at or above your amp's minimum rating. Most AV receivers handle 6 and 8 ohms; confirm 4-ohm support before pairing low-impedance speakers. Wiring two pairs to the same terminals halves the impedance.
Impedance is how much a speaker resists the electrical current an amplifier sends it, measured in ohms (Ω). A lower number means less resistance, so the speaker draws more current from the amplifier at the same volume setting. Home speakers are almost always rated at 4, 6, or 8 ohms.
That rating is a nominal figure. A speaker's real impedance swings up and down with frequency, and many "8-ohm" speakers dip well below that in the bass. That's why amplifiers that handle lower impedances comfortably tend to drive real speakers better.
| Rating | Demand on the amp | Typical speakers | What to check |
|---|---|---|---|
| 8 ohms | Easiest | Most home theater and bookshelf speakers | Works with almost any receiver or amp |
| 6 ohms | Moderate | Many towers and mid-range models | Nearly all modern AV receivers are rated for 6 ohms |
| 4 ohms | Hardest | Some audiophile towers, car audio | Confirm the amp is rated for 4 ohms; budget receivers may run hot |
Lower impedance isn't better or worse sound. It's simply a different electrical load. A 4-ohm speaker paired with an amp built for it can sound superb; the same speaker on a receiver that isn't rated for it can overheat the receiver or trigger its protection circuit.
Look for the amplifier's minimum rated impedance. Two examples from gear we recommend:
As a rule: a speaker's impedance should be at or above the amplifier's minimum rating. Higher-impedance speakers (say, 8-ohm speakers on an amp rated down to 4 ohms) are always safe; they just get a bit less power.
An amplifier delivers more power into a lower impedance, which is why spec sheets list power at both 8 and 4 ohms. A well-built amp with a strong power supply comes close to doubling its power as impedance halves. For example, the Aperion Energy Pro E3H that runs our front speakers is rated at 600 watts per channel into 8 ohms and 900 watts into 4 ohms. When comparing amps, compare power at the same impedance, ideally with all channels driven. More in how much amplifier power you need.
Some AV receivers have a 4/6/8-ohm setting. On many models, the lower setting reduces the voltage the amplifier can deliver to keep it cooler, which also limits maximum power. Follow your receiver's manual. Many manufacturers recommend leaving it at the default unless your speakers are rated below what the receiver supports, and good ventilation matters more than the switch for keeping a receiver cool. See receiver placement and ventilation.
These two specs often get confused. Sensitivity (in dB) tells you how loud a speaker plays with a given amount of power; impedance tells you how much current it draws. A high-sensitivity speaker like Klipsch's horn-loaded models needs little power to play loud, even if its impedance is low. When choosing an amp, consider both. And for long cable runs to low-impedance speakers, use heavier wire; see speaker wire gauge explained.