The Facts

• Parallel wiring in the mobile subwoofer realm involves wiring two or more woofers so that the impedance drops, for an increased amplifier load that boosts power output to each woofer in the chain. Impedance is the amount of resistance electrical signals encounter along a wire; the longer the signal travels, the greater resistance builds. In speakers, impedance on a wire occurs at the voice coil windings connected to the speaker input terminals. Parallel wiring is a common solution for wiring multiple 8- or 16-ohm woofers closer to the amplifier's target 2- to 4-ohm range, where most mobile amplifiers provide optimal performance.
  
  

Series vs. Parallel

• Series and parallel wiring are often confused, but series wiring is designed to increase impedance, with parallel reducing it. Wiring subwoofers in series has the net effect of reducing overall volume, which may be desirable in forcing a lower subwoofer output in relation to other system speakers. Series wiring also is used to wire two or more low-impedance woofers to a higher impedance with which the amplifier is more comfortable. Nearly all mobile amplifiers become more stable as impedance increases, and less stable as impedance decreases. Parallel wiring gets to the electrical limits of an amplifier faster, as all amps have a threshold at which they overheat or go into protection mode from a load that is too great.
  
  

Series/Parallel

• Series/parallel wiring works when you want multiple woofers in a system for more output or increased visual effect. In theory, you can wire any amount of speakers in a system using series/parallel, as it's always possible to keep the overall impedance within the target impedance range of an amplifier.
  
  

Wiring in Parallel

• Parallel subwoofer wiring daisy-chains the two positive terminals of each woofer with the positive terminal of the amp. The same is true for the negative terminals. The two subwoofers connect through their shared connection with the amplifier, achieved by jumping the two positive and two negative terminals on both woofers.