Impedance Curves
An impedance curve shows what load the amplifier really sees as frequency changes. It is one of the fastest ways to confirm resonance, box tuning, and whether the speaker dips lower than the label suggests.
Tiny Version
A tall peak usually marks resonance. A double peak with a valley between them usually means a ported box. The lowest dip is the load that matters most for amplifier stress.
How To Read It
- Single tall peak - free-air or sealed-box resonance.
- Two peaks with a valley - ported box behavior. The valley is the tuning frequency Fb.
- Lowest dip - the true minimum load the amplifier has to carry.
- High-frequency rise - voice-coil inductance pushing impedance upward.
Why This Matters
- A nominal 4-ohm speaker does not stay at 4 ohms everywhere.
- Minimum impedance matters more for amplifier stability than the badge on the box.
- The impedance valley is one of the cleanest ways to confirm a ported enclosure's real tuning.
Common Mistake
Do not read only the big resonance peak and ignore the lowest dip. The peak looks dramatic, but the minimum impedance region is what usually tells you how hard the amplifier is working.