I'm finally building my speakerpage kit and ran into a problem. when I reconfigured the box size for my situation I didn't take into consideration clearance from front to back for the 1.5 diam by 4" long port (after having made all the sides with dadoes and all). Now I'm having to add pieces to the inside to take up space so I can make the sides longer. My question is, what is the minimum clearance I need for the port? I think I read somewhere you need at least 1/2 the diameter of the port for clearance between the end of the port and the back (or front as is my case).