New box design

I like to think up things i haven't never seen done so let's get some opinions in here because i wanna see what people think how this would work -

I don't feel like drawing a pic so i'm going to rely on your visualizations to see this box in your head.

Let's take a 12" sub.

Let's put it in a ported box at 2.5 cuft. Tuning... thats the interesting part.

Ok, so build a box with 5 walls, not 6, 5. Leave the rear wall completely off.

Now, let's say for quick number crunching, the box is as follows - (all external)

16" wide x 16" tall x 16" deep with no rear wall.

Now, let's build another box with no sub cut out, again with 5 walls, not 6.

Dimensions for this box is as follows - (internal)

20" wide x 20" tall x 20" deep.

Put this box over the other box to where the side with no wall is on the same side as the sub.

Now, we connect the boxes together using nothing but All-Thread!

The result -

a ported box for a 12" sub in 2.5cubes ported with a port that circles all the way around the sub in a square that is 4" wide all the way around.

How in the hell can that be calculated and what on earth am i thinking would it sound like?