low frequency drop off at high volume

I just recently removed the stereo from my 98 S10 and installed it in the 05 dodge magnum I just bought. The system consists of an Alpine Head unit, boston acoustics highs, and a Diamond Audio CM3 12" sub. The sub is powered by a Rockford 1200 watt amp. When the sub and amp were in the small truck they would hit so hard my vision would start to shake. Now that they are in the bigger vehicle that has more airspace they play louder at low volume, and then slowly drown out the more volume I add. At low volume the sub overpowers the highs, and at high volume the highs and lows achieve a satisfactory balance, but the extreme low end disappears. The box the sub is in is most likely too small because it had to fit behind the seat of an s10, and I think this could be a major culprit behind the issue. Will a bigger box solve the issue? After reading about clipping I also think that could be a problem, but I didn't have this issue in the truck and no settings have been changed. I'm at a complete loss, any ideas? Great forum/website by the way, glad I found it.

i would also check for a current drop at high volume.. but i think u mite be rite.... the box for the s-10 undoubtedly probably matched the acoutics of the s-10 better for the type of sound u were lookin for..... i would probably check into a new enclosure... especially if there isn't any kind of voltage drop....there can be only one.......

Seems like the enclosure is incorrect for the vehicle and you are clipping the amp. What is the model number of the amp???

If I'm up on what rockford has out right now, it's from 2 generations ago. 1200watt (they're exaggerating trust me) I can't find the box and I'm too lazy to go out to the car right now and look at it. Anyways, I have it bridged, and for some reason the Gain for the right channel which as far as I know I'm not using actually has some effect on how hard it plays. What is that all about? The positive is coming from the left side. Anyways, I turned the right gain all the way down, and then set the left channel gain where I get no distortion, it hit's a little harder, but not hard enough for my tastes. I checked the volume of my current box, and it should still be within the recommended specs for the sub. With the same amp bridged would 2 subs hit harder then 1, or would the reduction watts per sub make it play at the same level? I can pick up 2 12" audiobahns for 100 bucks from my friend if it would be worthwhile. Thanks for the replies guys.

I finally had time to check the model on the amp, and you're correct it is the 401S. Big step downhill in quality from the Rockford's of old. I remember the Rockford 800 watt amp from about 10 years ago that was simply amazing. I'm almost positive the subs he has for sale are DVC's. Where exactly does clipping occur? In the amp or in the sub? I've heard the same single diamond sub I have absolutely pound and not distort. Mine is barely flexing, and it starts to sound like crap. Most likely just the cheap amp powering it I'm guessing.

First thing is you NEED to adjust BOTH gains to the same level.  If not you will never get the system to perform how it's supposed to.

Clipping occurs in the amplifier.