i just had a 15 inch version of the same sub i had before in which was a 12. The box lays flat in trunk with sub up, port towards trunk. The 12 hit the lows better then this 15. It really REALLY sucks... cause when u pay the extra money to get a 15 and pay for someone to make the box, yea this blows. The 12 was facing towards cabin as well as the port. Im thinking that may have something to do with it. The 12" box was 2.5 cu ft tuned to 33 hz. this 15 inch box was about 4.0 tuned to 34 before displacement, not to mention there are 2 bracing posts in the box. With all that said im wondering if the tuning is now higher because of that? i could actually FEEL the 12... i can hardly feel this 15.. i thought it was supposed to be the other way around. someone let me know. ive fed them both the same amoubt of power, about 1000. thx.