I just finished building my box last night.... Double baffle,Fiberglass,etc... My box after bracing and before the Port was 8.25cuft(internal)I have 119 sqin of port tuned to 30hz. After the displacement of the port I now have 5.85cuft. Now is my box 8cuft tuned to 30hz OR is it 5.85cuft tuned to 30hz??? And would that be too small for an 18?? thanks