Speaker Impedance - Series and Parallel

Series:

Z_total = Z1 + Z2 + Z3 + ...

Parallel (two speakers):

Z_total = (Z1 * Z2) / (Z1 + Z2)

Parallel (equal impedances, N speakers):

Z_total = Z / N

Mixed series-parallel:

Solve in stages. Combine each series or parallel group first, then combine the group results.

Worked example - two DVC 4-ohm subwoofers:

Each subwoofer has two 4-ohm coils. If you wire each sub's coils in parallel, each sub becomes a 2-ohm load:

Z_sub = 4 / 2 = 2 ohms

If you then parallel the two 2-ohm subs, the final load is 1 ohm:

Z_total = 2 / 2 = 1 ohm

If you wire each sub's coils in series, each sub becomes an 8-ohm load:

Z_sub = 4 + 4 = 8 ohms

If you then parallel the two 8-ohm subs, the final load is 4 ohms:

Z_total = 8 / 2 = 4 ohms

If you series the two 2-ohm subs together, the result is 4 ohms, not 2 ohms:

Z_total = 2 + 2 = 4 ohms

Bottom line: with two DVC 4-ohm subwoofers, the common all-coils-used symmetric wiring options land at 1 ohm or 4 ohms. A true 2-ohm final load is not available from that pair without changing the woofer or voice-coil configuration.