this is what you need to look at

see if there are either 1 or 2 positive and negative terminals on the sub (should have one of each on each side or just one set on one side). if there are 2 sets then you have what is called a dual voice coil sub, this sub either comes in a dual 4 or a dual 2 design. if you only have one positive and negative terminal you have what is called a single voice coil sub. depending on how you have them wired from there depends on the impedance.

from there we can answer your question.