Impedance and Wiring Subs

Impedance and wiring subs is arithmetic: identical drivers in parallel divide the load, in series they add it. The skill is landing on a load your amplifier is rated for, while using the power it can actually deliver.

Nominal, minimum and Re

"8 Ω" is a nominal figure. The real impedance peaks at resonance (and at the box tuning frequencies once mounted), dips above it, then rises with frequency as coil inductance takes over. The DC resistance Re that a multimeter reads is lower still. B&C's published data for the 18SW115 (8 Ω) shows it clearly:

Minimum impedance is what the amplifier has to survive, so wire to that, not just to the nominal. See testing a driver with a multimeter.

Parallel

Positive to positive, negative to negative. For n identical drivers the load is Z / n.

• 2 × 8 Ω = 4 Ω
• 4 × 8 Ω = 2 Ω
• 2 × 4 Ω = 2 Ω

Series

Positive of one to negative of the next. Impedances add.

• 2 × 8 Ω = 16 Ω
• 2 × 4 Ω = 8 Ω

Series wiring also means a failed open-circuit driver silences its partner.

Series-parallel

Four 8 Ω drivers as two series pairs (16 Ω each), with the pairs in parallel, give 8 Ω. That puts a four-cab stack on one channel at a safe load, though at 8 Ω the channel delivers less power than it would into 4 Ω.

Power into the load

For an amplifier holding a fixed output voltage, P = V² / R: halve the load and power doubles, until the amplifier's current limit or power supply runs out. That is why amp ratings fall short of doubling from 8 Ω to 4 Ω to 2 Ω. Bridging puts the load across two channels in antiphase, so each side sees half of it: a 4 Ω bridged load behaves like 2 Ω per channel. Check the amplifier's rated minimum load per channel and in bridge mode before wiring. See amp matching and 4 ohm vs 8 ohm.

Wavemark options

• WM1850/8: 8 Ω, 1800 W AES. Two in parallel make a 4 Ω pair.
• WM18X451: 8 Ω, with a 4 Ω option, 1800 W RMS. Choose the version that lands your cab count on the load your amps are rated for.

Wire cabs consistently and check polarity across the stack: see Speakon wiring.

Sources: B&C Speakers published data for the 18SW115 (8 Ω), checked October 2026; Wavemark WM1850/8 spec sheet and WM18X451 product data. Series and parallel loads and P = V²/R are standard circuit theory.