cant believe im asking this one..

its been a while since ive built a box, but im building a vented box for my ixl's, and im trying to figure some stuff out. the subs are looking for .7ft each (i have 3), so im going to need 2.1 ft net, and throw in displacement (which im guessing is about .45ft for the 3) were at 2.55ft gross.
now i know i need 16 inches of port per cubic foot..now do i multiply that by my net or my gross measurements?

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