preamp inverts polarity

preamp manufacturers say both speakers, if you only do one then the speakers are out of phase.  that is one woofer goes out while the other goes in thus canceling the bass out.

The speaker cables are marked differently so you can get both speakers wired consistently.  They are not made of different materials designated only for + or - . 

Are the tires on your car for only going forward?   Reverse the wires and be done with it.

genez, the positive and negative cables are different as i posted in an earlier post (4th post)
" Grost chose to construct the negative/ground cable from a mix of conductive composites and wire. The positive lead according to the literature, on the other hand, employs hundreds of stands of microfiber saturated in proprietary liquid ceramic.

"Is "phase inversion" the same as "polarity inversion"?"

Good question.