port help

[mcbuggin 10+ year member]

I have 6.75cf net for 2 HDc15's and to have the right port opening I need to add 10sq in. now I have some 3in inner diam. pvc to get close to 10sq in would I need to add 2 of these or how many sq in. is in a 3" diam. opening. Thanks

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[dannyz122001 10+ year member]

you need to add another 10in^2 in addition to the one you have now?

 

[mcbuggin 10+ year member]

yes it's an old box that I had my BTL18 in

 

[mcbuggin 10+ year member]

modified an old CRX style box and want to see what numbers I get before I decide to wall it off currently have 85in^2 but need closer to 95