What impedance will your amp actually see?
Pick your drivers, how each voice coil is wired, and how the drivers combine. You get the final impedance your amp sees, plus a diagram of exactly the wiring you picked. A DVC sub's real per-coil rating drives the math, not a guess.
Driver & Wiring Setup
Result
Why the amp sees a different load on different notes ("impedance rise")
Everything above is the driver's nominal impedance — the number on the box, and the number your amp is actually wired for. (A meter across the coil reads its DC resistance, usually a little lower, though some drivers read a little higher: JL Audio's 12W3v3 measures 3.56 Ω on a 4 Ω coil, its 10W0v3-4 measures 4.28 Ω.) A real voice coil's impedance isn't flat with frequency. In a sealed box it rises to one peak at the box's resonance. In a ported box it peaks twice, once below the tuning frequency and once above it, and dips close to the DC resistance right at tuning — so at tuning the amp sees its lowest load, not its highest. A normal, well-documented electrical property of voice coils in boxes, not a wiring mistake or a bad amp. See the Troubleshooting page's "amp seems to run out of power" row for the symptom-side explanation of the same effect. Wire to the final impedance calculated above; don't chase the resonance bump as if it were a mis-wire.