27.5 wide
15.75 tall
20.5 deep
Port is 6x13.75 inner dimension
It uses left side of box as common wall Goes down the back of box, once it's 6 inches from right side it stops and another wall goes back to the left utilizing the port wall insie of box then it is 3 inches from existing port wall with a /\ shape.
So from top view beginning of port looks something like
|***********************|
|. . |.^^^^^^^^^^^^ |
|. . |.3in /\_______|
| 6in. |..............sub....|
/\ both measure 5 inches
From inside front panel of box to port wall is 9inches
There is not double walled just 3/4 for all.
Hopefully this helps. Not sure how else to explain it considering it doesn't seem like a normal design.