from audiobahn's website
Q: On my Q series sub, why are there 2 + and 2 - terminals on each voice coil?
A: There are 2 + and 2 - on each voice coil. This is so when wiring the subs together you do not need to try and fit both wires in the same hole. You do not have to use both on each coil, but it will let you use a larger wire. Think of them as Y connectors. Both + and both - go to the same place on the same coil. You can wire as normal and only use 1 + and 1- on each coil.