What i do ifthis happens is very simple, i've got an old speaker, only a 5w or something like that, on that the terinals are marked - and +, i've cut everything away, cone, dome, edgeing, suspension just leaving the 2 wires and the voice coil. wire up your speaker wires to the now ripped to bits speaker, if the voice coil jumps out you've got the wires on the right way, if not then the - and + wires are on the wrong terminal, swap them just to be sure. once you know this then whatever colour is attached to the - is the - and viceversa.
its easy to test a speaker which hasn't got the - and + marks on them (like the standard ones) simply stick a AA battery onto the speaker terminals, if the speaker jumps up, then whichever terminal is attaced to the + end is the + terminal, if it goes down, its the other one.
as long as both speakers are wired the same, its not really a big deal for mids or highs, but bass will be affected as the speaker is designed to pump outwards not inwards.
hope this helps
