I am in great need of help. I have no idea of how to do this. And I cant find a good box clac either. But I need a ported box for 2 Fi 18". Each sub is suposed to have a box that is 5-10 cuft @ 30-37Hz. But idk how big or what it should be tuned to for 2 subs? The box is what makes a sub good so i need help matching these 2 subs to their soul mate box.

what are your dimensions (vehicle). I would go with something like 12 cubes @ 33-35hz.

I was told the same thing on another forum. And its going in a silverado (yeah tiny I know) but im taking the back seat out so i dont know exactly what I have to work with yet. and does anyone know a realy good box calc

ok I found a box calc but can you tell me if anything is wrong with this? It should come out to 11.8 cu ft @ 32.5 Hz. ok so to this site http://www.soundsolutionsaudio.com/home/boxes/sideboxcalc.html
and then type these numbers in order going down in the red. (sorry for the inconvinence but this is my final step before the boom boom)

40
35
20
20
.75
4.5
0

I just need to make sure Im not an idiot and did something stupid before it final. and its for 2 Fi BL.

3/4 inch isn't thick enough. I would use 1" doubled up and braced like a mother. Otherwise your gonna get crazy box flex.

If its a silverado i dont think your gonna fit 2 18s ported unless you wall it off. Not to mention I hope you have alot of money for amps and a charging system to back it up.