If you know which of the cables connected to which terminal on the speaker then you can find out, though surely if this was the case the speaker would be labelled?
Take 2 runs of cable and attach them to the speaker terminals (one to each), then take a 9V battery (the square one) and touch the two cables to the battery terminals, the speaker will pop, and if it pops "out" then the positive battery terminal is connected to the positive speaker, if it pops "in" then it is the wrong way round...dunnoif thatll help you.
Otherwise check out a Haynes Manual.