Subwoofers moving but no bass?

"how are subs wired?"

The subs are wired they way an installation company wired them for my first amp:



"Make sure polarity is the same on both subs"

How do I do this. Sorry but I know very little about this stuff.

"try a different amp or different subs and see which one is causing the problem"

I used to have another amp connected which worked fine. I had one of my subs out of the box testing it so is it possible when I put the sub back in the box I unknowingly wired it in wrong. Could that cause this problem.

Thanks for all your help guys! I checked the sub wiring and found out I did switch the phase of it. I unknowingly had the speaker wire running to the wrong terminals. I switched it all correctly and it sounds perfect now.