Wire two or more speakers in series, parallel or a mix, and see the impedance your amplifier has to drive — plus whether that is safe for it.
Use the nominal impedance printed on the back of each one.
| Two 8 Ω speakers | Load | Power drawn | Watch out for |
|---|---|---|---|
| Parallel | 4 Ω | Amp works harder, roughly doubles output | Halves the load. This is what trips receivers. |
| Series | 16 Ω | Amp works easier, output drops | Safe but quiet, and one speaker's behaviour affects the other. |
| Series-parallel (four speakers) | 8 Ω | Same as one speaker | The right way to run four speakers off one channel. |
Parallel: 1 / Z = 1/Z₁ + 1/Z₂ + … — the load always
comes out lower than the smallest speaker in the group. Two 8 ohm speakers make 4 ohms;
four make 2 ohms.
Series: Z = Z₁ + Z₂ + … — the load comes out higher.
Two 8 ohm speakers make 16 ohms.
Series-parallel: pairs in series, then those strings in parallel. Four 8 ohm speakers come back to 8 ohms, which is why it is the standard way to run four speakers off one amplifier channel.
Halving the impedance asks the amplifier for roughly twice the current. A good amplifier delivers it and gets warm. A modest one distorts, goes into protection, or in the worst case damages its output stage. "More speakers, more sound" is how people cook receivers.
Nominal impedance is a label, not a measurement. A speaker sold as 8 ohms typically dips to 5–6 ohms somewhere in its range, and some dip to 3. So a calculated 4 ohms is really "4 ohms and sometimes less" — which is why the safe answer leaves headroom rather than landing exactly on your amplifier's stated minimum.
If you are picking an amplifier rather than wiring one you already own, the amplifier matcher checks impedance safety against every model we cover.