I'm planning on building a sub box and I'm trying to save money buy cutting up an old one I have.(to make two separate boxes from a dual 12") The original box is made of mdf. I need to replace one side on each separate box but I don't have mdf. I have birch plywood however. JL's site says that birch plywood is a good alternative if mdf is not available. My question is, is it ok to mix different types of wood on the same box? I plan on using the birch plywood for one side on each of the boxes. How will this affect my sound and the subs?