just want to know what the margin for error is when building a ported box. if i'm off by like 0.1 cubic feet will that be to much or will it not make much difference. i need to make a box that has 2.5 cubic feet inside after the sub is in and the ports are in, i know how much my sub displaces but i don't know how much the two ports will displace(2x- 5"dia x 8.5"long). i have made a rough guess and i figure it won't be off by much, at most .1, if thats too much i would like to know