One thing to try is swapping the pos and neg on one speaker. Even if the they are both wired the same it may help. If its even worse when you switch then change it back. Also the specs dont really mean much. There really is no way to tell. You really arent gonna get much bass out of 6 1/2. Bass is physics. Its all about displacement. With speakers thats cone area times x max (stroke) just like in an engine. You would probably be better of going with a 6x9 if you can manage. Sealing off air leaks can also help as air leaks will cause a loss of bass.