im running whats in my sig and after displacement (sub,port) my box is on the small side. In the long run I will have to build a new box but its just not plausible right now I've already dumped more $ than expected on the new setup. The subs are in one box with individual chambers and with the port length being 3x11.89 its taking up a lot of displacement not too mention its a lil too close to the back wall. Each chamber is 1.1 cuft and theres 2 chambers. I was gonna cut the middle wall to add space and change to external ports but is the formula the same?