Right now I can't remember which part is part F. Once I get home I will look at my print and get back to you.
You will love this sub with music once you build it.
John

Now I know what part F is after looking at the print. Lets see if I can explain it. All you need to do is grab a piece of scrap plywood that is about 2 inches long. The one edge is flat but the other edge needs to follow the angle of the baffle that holds the driver. The angle is real small something like 2.7 degrees. This piece is used to brace the panels in the center. So make sure you have a line drawn in the middle/center front and back and also up and down of the flat outside panel. You want to know the center of the outside panel to place this piece. So this piece is about 2 inches long. Make sure its wider than the opening. I would use the edge of the angle baffle that holds the driver to get the angle that baffle is at. So place the block so the front edge of the block is in line with the center line you have drawn and the other edge flat to the outside fall. Take a pencil and mark a line using the angle baffle to get the angle. So now you should have that angle so cut the piece. Now you need to make a radius from the front corner that is cut at the angle to the flat piece. I think you can use a quarter to get that radius. Once you cut out the raidus, mark a center line of the thickness of the piece on that radius. Now take it to a sander and sand it down to a point, like a knife edge. Just the radius, so blend that into the flat piece. It should look like a tip of a knife when you get done. Now put some glue on it an place it at the center between the two panels. Tap it in and let it dry. Its just there to brace the panels.

pic2

pic4

Thanks that really helps!  

I hope to get it all together in the next few weeks and will post a couple pictures.