subwoofer box dimensions needed

(...ok, I double-checked this post...)

W 30.25 X D 23.5 X H 15.5 is overall box size, correct?

It depends on how you want to construct your box.  The thickness of the MDF is going to have to be taken into account.  If you make a full size top and bottom, those panels would be 30.25 X 23.5  That's the full width and depth of the box.

If that's the case, then the vertical panels will be shortened by the thicknesses of two layers of MDF (the top and bottom panels).  Instead of being H 15.5, the actual panel would be H 14.  Front and back, side and side all would have a 14" height.

If you want the front and back panels to overlap over the edge of the side panels, they would be full box width, meeting the corners of the top/bottom panels.  W 30.25

If that's the case, then the side panels width  would be lessened by the thicknesses of these two overlapping front and back panels.  Take 1.5" off the box depth to get the panel size.  That would be 22".  The inside divider panel will be cut the same as the side panels.

2 pieces:  30.25 X 23.5  (top and bottom)

2 pieces:  30.25 X 14  (front and back)

3 pieces:  22 X 14  (side and side and middle divider)

Draw out a cut plan on a sheet of MDF if you want to be able to talk them into cutting these out for you.  You have somebody to cut the holes too?  ;)

Any braces inside that bad boy?