1.5 cubic feet as square as possible port on outside of box (try sub up port back and sub loaded off the driver side, port back, also play with placement of the box) start with tuning of 50hz and start chopping port length until u get the biggest number //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif With one 15 id stick with 2 4" aero's. Theres alot of variables when it comes to spl so its really all about test n tune. Those first hints tho will help ya in the right direction - btw do NOT play music with this enclosure - the extremely small enclosure causes an extreme peak in freq response - great for spl but ull end up damaging the woofer if u try to play music with this enclosure