How Speaker Impedance Works

Impedance is the resistance a speaker presents to the amplifier's output — but because audio is a constantly changing signal, it is not a single fixed number.

Measured in ohms

Impedance is measured in ohms (Ω). A speaker's rated figure — usually 4, 8 or 16 ohms — is its nominal impedance: a representative average, not a constant. Measure the voice coil with a meter and you'll see the DC resistance, which is lower, often around 6Ω for an 8Ω speaker.

Why it changes with frequency

A speaker is a coil of wire in a magnetic field attached to a moving cone. That combination reacts differently to different frequencies, so impedance rises and falls across the audio band. It peaks sharply at the driver's resonant frequency and climbs again at high frequencies. The nominal rating is roughly the minimum in the usable range.

Why the amplifier cares

Lower impedance lets more current flow, so the amplifier delivers more power — but also works harder and runs hotter. Every amp has a lowest safe impedance. Go below it and you risk overheating and protection shutdowns.

• Higher impedance (16Ω) → less current, less power, an easy load.
• Lower impedance (4Ω, 2Ω) → more current, more power, a demanding load.

Keep learning

• See the practical difference in 4-ohm vs. 8-ohm speakers.
• Learn what goes wrong in what happens if speaker impedance is too low.
• Combine speakers correctly with how to calculate speaker impedance.