Are my dimensions/displacements correct?
 

Hey Guys,

Not my first system, but my first system for my BMW and I want it to be right. I've never bough a prefab, always built my own, but typically they were sealed, or I never took the time to account for sub and port displacement in slot ported boxes :thumbsdow.

I'm going to be firing my sub and aeroport through the rear ski port, so I want it to be right.

I'm running a Sundown e8V3 off a JBL MS-A5001 at 4ohms.

Its going to be a wedged box to accommodate the pitch of rear seat.
Dimensions are as follows:
W:21 H:15.375 D(Bottom):10 D(Top):5
This equates to 0.93945 cubes.

Now this is where I get lost.
Sundown states the sub displacement is .05, So i'll go with that.

That brings my area to .88945

Now port displacement, the real confusing part for mewhen figuring out the actual displacement.

I'm going to be running a single 3" aeroport. Port calculator says it should be at just under 18" to reach 35hz. So my math is as follows.
3.14*4.5*18=254.34
254.34/1728=.1471875 Displacement total

So with all displacements considered, this leaves me at .7422525 cubes. Which ideally where I want to be around the recommended .50-.75 cubes for the e8v3.

Does this math sound correct? Especially the port displacement.

Thanks for dealing with a redundant question!