I just got my 5.1 system with the 12 inch subwoofer and I am not an expert but I think I have a pretty good ear and the bass seems rediculously boomy to me.  I got the 12 because I love good strong bass, especialy for HT but it seems like in every seen of every movie I have tried that has bass,  I just get this boomy low almost continuous bass and it lacks upper end punch.  In Saving Private Ryan I tried a bunch of seens and like I said I would get tons of boomy low bass from background explosions and machinery but then close up explosions would lack that upper end punch that hits you.  I have a 14 x 14 room that has big 6 x 8 opening on one side into the next room which is very large.  I have thick plush carpet and big fluffy couches.  I have moved the woofer to various locations.  I finaly placed it in almost the center of the room to make sure I wasn't just getting too much reflection from the wall.  I have a Kenwood THX select  VR-510 reciever.  The crossover is not selectable and the manual doesn't say what it is set at.  I tried setting the subwoofers crossover at various settings and I set all the levels with the spl meter.  What do you think my problem might be?  I played with the phase a little bit and that didn't seem do do much.