Hello everyone. I got a question regarding my sub. first off my sub is about 7-8 years . There is a switch on the back that says (polarity) and the switch can be switched to (reverse) or (normal). what is that for? Thanks in advance!
BTW it has always been on normal.

The polarity switch is useful for achieving the best blend with your main speakers. What it does is switch the phase of the sound coming out of your subwoofer. The effect of flipping that switch would be the same as hooking up a speaker wire backwards (positive to negative terminal and negative to positive terminal).

Why would you want to do this? Well, in certain arrangements (say one half-wavelength distance btw a main speaker and the sub), your sub's bass could actually be cancelling out bass coming from your main speakers. Flipping the polarity switch would fix that problem.

Well put. Thank you pmbuko!