actually i am a woodworker by trade and hdf and mdf is better to build sub boxes with than ply
reason for this is hdf and mdf is denser and doesn't resonate as much as ply does witch mean the box is deader acts like sound deadner and yes i know this to be true i used to be the head woodworker at my local sound shop and we even tested the material against ply and particle board and mdf won hands down