center fire port

[christianwardell]

I want to make a box for 2 fi bl 12s the dimensions will be 32w x 13h x 26d and i want to tune it to 35hz but i dont know how to make a center port. i have used the re audio box calculator for all my other boxes.

i have been trying to figure this page out but i dont understand all the numbers. i would like to make a box like picture f) or g)

http://www.stevemeadedesigns.com/board/topic/9336-8-basic-diagrams-on-how-to-measure-port-length/