Now i know the reuptation of kicker subs around here (mainly l5/l7/solo x). But just to start i wanna say don't flame me, that's not why i'm posting, i'm posting simply for your guys's heightened knowledge of car audio. First of all i have a Kicker '02 15" L5 subwoofer in a ~3.0sq ft sealed enclosure custom built. It is powered by a Premier PRS-X720, which is said to have between 700-800 rms when tested. So this should be plenty for the sub. I've set the bass boost to 0, and have the low pass set to 125hz because i control the LPF from my head unit(premier DEH-P770MP) which stays at 50 or 80 hz at 0 or +1 gain. Do you guys have any good reccomendations of how to improve SQ, i could care less about the spl of my sub, i just want to be able to really feel those lows that take ur breath away, that i've heard with this identical sub in my friends car, which i then bought off him. It just doesn't sound the same as it did in his car.
If you're wanting to improve the low frequency extension of the sub I would recommend deadening your trunk. That's about all you can really do aside from changing to a vented enclosure. If your friends car was larger than yours, his cabin gains would be higher at a lower frequency. So if his car seemed to have a better low range extension than yours that could be why. As for SQ, SQ isn't a measure of how low a subwoofer will play, it's a measure of how even and true a subwoofer will play the frequencies it's fed. The best bet for you is to use some form of deadening in the trunk of your auto first, if you're still not satisfied I would recommend getting a low tuned enclosure for the 15, or possibly turning down the gain and feeding it a little bass boost in its place.