effects of volume in sealed enclosure?

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k, so the Vas of my sub is 3.31 ft(cubed). my owner's manny says:
at a volume of 1 ft(cubed) the F3 is 42hz and the Fmax is 62hz
at a volume of 1.25 ft(cubed) the F3 is 35hz and the Fmax is 50hz
so i'm guessing as the volume increases, the F3 and Fmax go lower. i'm trying to build a sealed box with the lowest F3 and Fmax possible and, of course, avoid infinite baffle. would you suggest a volume of 3 ft(cubed)?
if you havent got a specific driver bought, try modeling a few in winISD(free program). Flat response in car is not the lowest tuning frequency. You need to find the tuning frequency of the car first, a roll of of ~40hz is expected for a flat response in car due to cabin gain
two other things to consider when shooting for the flatest respone possible, cabin gain and the frequency response of the driver itself. The cabin gain is basically dependant on the volume of the car and a fair approximation can be made, I have seen formulas on this site. The frequency respone of the driver is almost always ignored in simulation software, usually the efficiency number is used across all frequencies. Unfortunately the speaker has peaks and valleys in its response, and a roll off of its own. You can't really do anything about the peaks and valleys, but you can somewhat compensate for the roll off by making the box such that it has a resonant peak as the drivers response rolls off. If the frequency response is available try to feed it into the simulation software, then play with the box volumes and port sizes to lengthen the flat area of response. I have used this trick in the past to get an extra 10 or 15Hz of flat response, and I have never made a bad sounding box.
Have a very thourgh read through of the Infinity Perfect VQ manual on the Infinity website.

The VQ use metal insterts to chage the motor strength, altering paramaters.

The balanced enclosure looks to be 1 cubic foot with the medium Q insert.

If you want to slant it to bais it toward the very lowest extention then try 1.25 with no metal inserts.
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