how does this look for a first box

[barney91]

So I spent most of the night designing a box for four sa-15s

The box measurements are 48w x 17.5h x 36d which should put me at 15cf before displacement

The port is 16h x 11.5w x 28.9d which should tune me to 30hz

After sub displacement and port displacemet the box should be around 11.78cf if the box is to small I can tune it to 33hz which puts me close to 13cf

Also subs up port back in the middle

The point of this post is to see if my math is right and if its a good box for the subs

Thanks in advance

Sorry no pics unless my friend let's me use his laptop later