The electrical resistance a speaker presents to your amp. Most home speakers run 8Ω; many car subs run 2–4Ω — it changes how much power your amp delivers.
Impedance is the AC resistance a speaker presents to an amplifier, measured in ohms (Ω). It isn't fixed — it varies with frequency — but manufacturers publish a nominal rating as a simple reference number.
Lower impedance generally lets an amplifier deliver more power (most amps roughly double output as impedance halves, within their design limits), which is why car subwoofers are often wired to 1–2Ω for maximum output. But every amplifier has a minimum safe impedance — going lower than spec risks overheating or shutdown.
| Context | Typical Home Audio | Typical Car Audio |
|---|---|---|
| Bookshelf/tower speakers | 6 – 8 Ω | — |
| Component speakers | — | 4 Ω |
| Subwoofers | 4 – 8 Ω | 1 – 4 Ω (wired) |
