Hey I have a single 12 inch magnum D2 in a sealed box that is 3.0 after displacemnt and i want to port the box. It is a dual chamber box for 2 twelves that is why it is so big. What I want to do is draw a circle cutout for one of the speaker whole that is 12.5 d then have two smaller round holes inside of that circle cut out. I am willing to buy PVC pipe with an elbow for each of the two wholes. What would the legnth and diameter of each of the two small round cutouts hve to be in order to tune the box to 35hz?