Large terminal is + small is -. Always is and always will be. Makes a big difference.
If you wire all of your speakers backwards, it does not make a difference at all. If you wire just 1 different than the others, it is called "out of phase" and you get a hollow sound from that one speaker due to canceling frequencys.
If you really want to check, get a battery like stated. Small one. No bigger than a 9 Volt. When you see the speaker move out, that is the correct way to go. If it goes inwards, incorrect.
If the battery + is on the speaker + and the batt - is on the speaker -, the speaker should move out until you remove the battery.(correct) If is goes the other way just switch it. ANY QUESTIONS???
Hope that helps.........................LT