Not trying to be an ass, but ive been in this business now for seven years. And you never ever use plywood. You should always use MDF wood, because even though the seams of the box are sealed plywood itself is very pourus and leaks alot of air.
ive been in the business for MORE 1.5 Years lol... i would have never considered plywood because i was a freshman when i started and the Seniors told me how it is! lol