I am about to install a system in my girlfriend's car and decided to go with some RF P212d4's, the older model with the removable magnet cover. Only problem is that the QTC of the box is rediculously low, meaning .488, and that is with the box only being a total volume of 2.4 cubes. So I am redesigning the box, since they only call for .85 cubes a piece I was going to shrink it down to 1.7-2.0 cubes but that only brings the QTC up to around .57. Now I know that with sealed boxes the smoothest response is around .707 but I can not get these subs to see that high of a QTC unless I put both 12's in a total 1 cube box, .5 cube for each sub which seems awfully small. So I am asking you guys for some help. Should I just go by what the manual says and build the box to 1.7 cubes and have the QTC at .57 or should I shrink it down more and try to bring it up? They are being powered with a Diamond D3 400.1 @ 1 ohm and she listens mainly to country music and some R&B. What would be my best bet, go by the manual or build or tremendously small box?