port calculation

I am trying to figure out how to get the right port size for my three 15's. I have the power acoustik mofo. For one 15 sub the specs say that i need to have two round port at 4 inch round dia and a length of 8.25 so 2 round ports at 4x8.25 each. So that is .09187 cubic feet per sub. So for three i need .28117. My real question is, since i want a slotted port not a round port i have to use the "Volume Calculator - Rectangular/Square Enclosures" that is on the "the12volt" site. Since i already know how long and Width i want the port to be i just have to play with the depth. When ever i type in how width, high and deep the port is do i also have to put in the thickness of the wood or not because the .28117 is the internall space of the port. Can someone also just double check my calculation of 2 round port at 4x8.25 each to see if it comes out to be .09187. Thanks allot guys

Uh... Your way off. It doesn't have anything to do with port volume. You need to download a box building program, WinISD is a good one. Then punch in all of your subs info and tell the program how many ports you want and it will give you the dimensions of the ports. If you go with a chambered box then you can go with 2 ports per chamber using the recommended port size. Certified Security Specialist

Always check info with a digital multimeter.

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whell i did that and just to make sure that the program is right i put all of the info in and i did a round port with the same tuning and box size and the port was longer by 4 inches on both of the ports so i would just like to do i single port for 3 15s but i am jus trying to figure out if i have to leave the thicknes of the wood off and make it a 0 when ever i type it in the Volume Calculator that its on this site or do i have to add the thicknes of the wood.