only 1 sub works

Ok, here is the setup.. I am running a Profile 80 x 4 amp, my plan was to run a set of 6 1/2" (4 ohm) off channel 1 and 2, then bridge channels 3 and 4 to run 2 Fosgate series 1 10" SVC subs. The dilemma.. I have wired the subs every way possible that I can think of 1 off each channel, series bridged, parallel bridged, series off of one channel, parallel off of one channel. The subs run together sound like complete garbage, flat, no tone, just basically a lot of fluttering. Now if I run just one sub at a time, it comes to life and sounds great. Either sub, either channel, doesn't matter, sounds great. But as soon as the second sub gets hooked up, straight back to sounding like crap.. I'm by no means an expert or a pro at installs, but have always done my own stuff and have never seen this happen. Any ideas?

Sounds like one sub is out of phase with the other one.Support the12volt.com

    And to rectify this out of phase problem you need to pull your woofers out of the box and verify you have the positive and negative connections properly connected to the appropriate wire. Chances are one of the woofers is not wired properly.    Or if you do not feel like removing your subs, just hook 1 (one) only one of your woofers up backwards. Positive wire to the negative terminal of your amp and negative wire to the positive terminal. DO this to only one of your woffers. If you do both you will be in the same boat you were in before.