cuz ur off on the math the 18s box with subs INVERTED net is 6.86 with subs in 6.36.. .25+.25=.50 6.86-.50=6.36..... that includes port displacement befor port its 7.69.. also if u think it will have port noise then tell me why is it i see builds with more 18s then that with port around 10x10 with out port noise??? and I WILL NOT GO AERO i dont like round ports i was forced to use a round port on my 10" type r box and i hate them allways will.... now i have seen builds of 18s in boxes of this size bigger 18s and sound grate... i have told u i have all ready checked all this math i have used soft ware also 6.86 DOSE NOT INCLUDE the added mdf to the face palate...