Audio and speakers
Speaker impedance
The electrical load a speaker presents to an amplifier, nominally 4, 6, or 8 ohms, which determines how much current the amplifier must supply.
Impedance is the speaker's opposition to alternating current, and it varies with frequency. The nominal label figure is a summary; the real curve may dip well below it. Lower impedance draws more current from the amplifier for the same voltage.
A receiver rated only for 8 ohms can overheat, go into protection, or distort when driving 4 ohm speakers loudly. Impedance also interacts with wire: a lower load makes cable resistance a larger share of the total and calls for heavier gauge.
A 4 ohm speaker roughly doubles current demand, so check for a 4 ohm rating before pairing and consider a separate power amplifier for low impedance towers. Keep cable resistance under 5 percent of the impedance, which for 4 ohms means under 0.2 ohms round trip.