ok my sonosub design calls for 2 3"D x 12.44"L ports. This will pass through (3) layers of 3/4" material. (2 inner-tube MDF, 1 outer-tube table-top layer) My question is: does the extra layer outside of the sonotube account for extra or less port length? Do I cut a 12.44" piece of pipe, or do I have to add/subtract 3/4" increments to compensate? hopefully this isnt too confusing a question. thanks!