Is there any reason why i can't use 3/4" plywood to build a sub box in the hatch well? I know youre supposed to use MDF or fiberglass, but whats the difference? I can seal plywood corners just the same, and its incredibly cheaper.

 

whats the big deal, a 4 foot by 8 foot sheet of mdf is under 20 bucks. i made a freakin huge box with 2 sheets.

hold a piece of plywood. break it over your knee. try that with mdf. now stick a 50 pound sub in a plywood box and give it a few thousand watts.

 

MDF isn't expensive. You can get a 4x8 sheet for around $20-25 at lowes/home depot. It's also uniformly dense, won't have any knots in it, etc; all together a much better material for building enclosures than plywood. Sure, there are alternatives but they all cost a good deal more (nice quality oak, birch, sonotube, etc).

In a nut shell MDF is cheap ($25 is dirt cheap in the world of audio - my fiberglass box is probably hovering just under $200 in supplies thus far). It also is extremely easy to work with and will never have any flaws, imperfections, etc.

Edit: mean brings up another good point, MDF doesn't flex much at all.

 

MDF is preferred over wood in speaker cabinet building because it controls cabinet vibrations/resonances better than wood. A wood cabinet when hit on the side will have a 'ring' to it, while a MDF cab will have a dull 'thud'. It really depends on how the cab is made though. There's no law saying you can't use wood. Plywood is much better than solid wood, as the ply layers tame things down a bit like MDF. For a car I'd think a plywood cab would be fine (3/4"). Do the right internal bracing and line it with something to absorb the back wave etc.