sketchup is one easy application to learn, take your time with it. make each piece or baffle at a time to its corresponding dimensions and youll end up with a box then you can cut circles and ports holes on the baffles them self. try it for a while youll get the hang of it.
I just downloaded the program last night, and sketchedup some boxes, but I can only save it to .skp file format. Is there a way where I can save them as .jpg or such?