Worf:
It does matter.

If you can't check the polarity (wire in-wall, for instance), here's how it's traditionally done:

1- Disconnect one of your mains, and move the other as close to the center as you can.

2- Set both for "Large in your receiver.

3- Play a mono signal through both speakers with a decent amount of bass.

4- Try switching the polarity of the center speakers' wires back and forth to see if one way has more bass. That orientation is the correct polarity.

::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::