I took the measurements of a HT cab and cut it in half height wise. I used 3/4" ply. Cut the tops of the cab straight on the table saw to size, then with a 3/4" scrap piece, draw a pencil line from the edge to 3/4" in on the boards for the sides (top and bottom of the board) and cut that over the table saw with the blade only going half way through the wood. then cut it so it is notched with a 3/4" by 3/8" cut out by running the board standing straight up over the saw blade at the right height again. Glue and nail together, you have a sturdy box. cut the baffle to fit and then cut the circle with a jig saw by finding the right diameter on line for your speaker. a half sheet should suffice, about 25 bucks. Good luck and watch your fingers.
TS is right, you should be able to find a cheap cab around your parts easily., maybe a little more than 25 bucks, but you wont have to deal with any of the labor.
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