Different subs react differently in different amounts of airspace. Another words without knowing what kind of subs and the thiele parameters for those subs there is no way to tell where your box is tuned. Check out Car Alarm, Car Stereo, Mobile Video, and Cruise Control Info for Installers, they have a lot of really good info on that site for someone trying to do their own install work, they even have a box building program which can help you design a box which will get you what you want out of your subs.