hello I would like a design for a single with dimensions of 17H, 40W , & 18D Mmaybe alll the WAY to 22 but sub will be to close to trunk wall ... on you tube thers a design double port the guy has It on a civic very nice.oh and tuned to 33 to 35

Try any of these guys. Or Argent Audio or the SSA store.

If you also want a dual port setup, make each port 15.5" tall (height of inside of box) and 2" wide, by 31.5" long. That'll give you about 4 cubes net tuned to 34 hz. that's with the 17x40x18 box.

thanks midnight thunder, but what would I have to increase to get the 5.0cuft or more. can do the 20 D and maybe 18 tall sorry , is 1 cu ft much of a difference ? its going to be set on a CROWN VICTORIA, THABKS FOR YOUR TIME

is 31.5" long for both sides ? or 31.5/ 2... any 45 angles ?i want something like this

YouTube - Fully Loaded 15" Fi BTL Subwoofer, Flex, Excursion

Yes, each port would need to be 31.5" long.

You can do 5 cubes @ 34 hz with a box that's 18"h x 40"w x 20"d with two 2"w x 16.5"h ports that are 26" deep each.

18x20x40 thats the outter dimentions(including the wood thickness)or thoes dimentions plus TOW.is that including BTL's hixmax coil displacement?thanks for your help!!

Oh oh is it better double port or just a single port?

Yes those are outside dimensions, and it doesn't matter if you have one port or two. You said you wanted a double port so I designed it with them. That design has 6.8 cubes gross, minus 1.35 cubes for port displacement, and .45 cubes for sub displacement.

How come in fi's website shows that 15 btl has as .21cuft displacment.where did you got the .45 cuft?can i add 45's on the corner of the ports thanks KU40

I guessed. And it doesn't matter. The .03 cubic feet between my guesstimated .45 cubes and the actual .42 cubes won't make a difference. And yes you can do what you want.