[TMTTS]

I have two rockford fosgate subs ( 12's). And a rockford fosgate 500RMS amp. When I first installed the sysytem it hit really really hard and was amazingly loud. I've had it for a couple months now. About a week ago I noticed that for some reason it wasn't hitting nearly as hard. I used to keep the subs on negative 3 and it would vibrate everything in my car... if I had something sitting in one of the slots under the radio.. it would fall out from the vibration. Now, I can turn my subs to positive 7 and it won't even budge and I can tell that its not hitting as hard along with my friends. Could it be because I don't have a capacitor or could it be my car battery needing to be replaced?