Well, I know there's a couple of writeups on how to DIY sub boxes, but I figured... "Hey, what's one more?" ..... I mean it's better than a slew of people filling up the DIY section with questions on how to change their stock headlight bulbs.....

Anyways, here's roughly what you'll need.

An Idea of what shape you'd like.
3/4" MDF
Fiberglass Resin
Fiberglass Cloth or Mat
Vinyl or Latex gloves (buy in boxes of 100 for $10.00)
Excessively cheap paintbrushes (about 10...)
plastic painters pails
Body filler
Sandpaper
Spreaders
Paint, Primer and Clearcoat
Rotary tool, or an angle grinder... better to have both.
Spin Saw or Jigsaw
Respirators
Silicone
Sound Deadening Material (Dynamat, Brown Bread)


OK, so here goes... Come up with an idea of a shape you'd like given the space you have for a box. Find out the recommended volume for the inside of the box and calculate the shape. Good estimates will work best here as most people I've heard from say that as long as you're within 20% of the recommended you'll be fine. I took the dimensions of my side peices, calculated the volume, and roughly estimated what it would be with the curves and such.

Use cardboard to create a template for the MDF peices. Trust me, it's 100x easier in the long run to do it this way. If you can, when you buy your MDF, if the place you get it at can cut for you, get them to... less hassle, less mess. If you need curves cut, you'll likely have to do that on your own. I got them to cut the basic shape, then I had the curves cut in later as well as the MDF ring. If you can get the curves cut cheaply, I'd suggest doing it, it's worth the few bucks, and again, less hassle, less mess.

OK, take your peices and test fit everything, make sure all the sides line up nicely. Cut some sound deadening material (Dynamat, Brown Bread), and cover the inner areas. Be sure to leave material OUT of the connecting areas (see pics) Using a heatgun and a roller adheres it much better than just a roller.



Next, Assemble the box... I found that using carpenters glue first, then reinforcing with fiberboard screws worked best and got everything together well... I may have over did it on the screws, but at least I know it won't flex. (about a screw every 2" I think I did...)



Seal the joints with silicone. Take your MDF ring, and some spare strips of MDF and position the ring wherever you'd like it. The best way is to use carpenters glue on the strips to get it to stick completely to the ring and the base of the box.





Wrap everything in a polyester fabric or fleece. Cotton shrinks. Get everything as tight as possible and staple the fabric to the frame of the box. MAKE SURE YOUR RING HASN'T MOVED! (or you just may find out you're screwed later on in the game.....)


You may find some fabric overlap, and here's where it gets tricky.... save this to last and do your absolute best to get all of the excess fabric to meet at one spot. CAREFULLY cut out peices of it at a timeuntil there's only a slight bit of overlap. Cut a small hole in the middle of the fabric inside of the MDF ring (see hole in above pic) so that your fingers can get through... add some glue to the inside of the flap and squeeze the parts together on the inside to make a seam on the outside, or as close to a smooth joint as you can. Cut off most of the excess fabric... keep a bit extra on the sides for fiberglassing purposes. Now... here's where the fun begins....
(Holy Sh*t this is getting long...)

Grab a respirator, the paintbrushes, fiberglass resin. Mix up a fairly large batch ( a quart?) and just soak the resin into the fleece... keep in mind if you get this stuff on your clothes, you're likely screwed (well, your clothes would be... you'll be fine actually) make sure to get pleanty of resin soaked into the MDF areas as to bond the MDF to the fiberglass parts. Let it harden (about an hour, possibly more depending on the type of fiberglass resin...In some cases it could be better to let it cure a day or so so that the box won't warp later... After, just brush on layers of fiberglass, put some resin on the box, add a piece of fiberglass cloth or mat, and paint over it with the resin so the resin soaks into the glass. About 7-10 layers is enough... make sure it doesn't flex... if you can press on an area with your thumb and it doesn't flex that'll be fine. Overglass the edges by about 1/2"-1"... this is in order to ensure all of the corners of the box are fully glassed over.


Sorry, I don't have pics of the fiberglassing part, or the body filler stage...
Once you're done with the layers, grind off the excess 1/2"-1" of fiberglass with a angle grinder or rotary tool (grinders are faster and easier) Grind out the excess fiberglass in the center as well. Mix and apply body filler, let it harden, shape and sand. Mix the filler as uniformly as possible in order to prevent pinholes from forming (these are a HUGE pain in the ass). Sand down until you get the shape desired. Try to get the sub ring as level as possible using a sanding block. Using a sanding block or hand sander (or anything with a flat surface) works best to maintain consistency. Do the regular Coarse, Medium, Fine process with sandpaper, as well as with wetsanding. Spray Primer Fillers are available to fill any hard scratches, but trying to sand them out works best.
[IMG] [/IMG]
Once sanding is done, apply primer, then coats of paint. Spray paint in light coats and as even as possible until you get the colour thickness you'd like. Then Clearcoat in the same way. (There's probably better forums on painting... I just kinda winged it....). If need be, remove any excess filler on any areas. As for terminals, I bought pairs of gold plated terminals, drilled a hole the size of the terminal screw, put in the terminal, and siliconed around the edges to prevent any air leaks. Silicone the inside where the MDF meets the Fiberglass, and apply some sound deadening material to the inner fiberglass parts so that the entire inside is covered in sound deadener.
Now, just wire up the sub, put it in, drill the mounting holes, mount it, and you're ready to go.




The sides and back still need to be finished... I'll likely get some black carpeting and cut it to size and adhere it in some way... This one sounds a lot better than the other boxes I've made... nice tight and clear bass
For those of you living in apartments (like me) and have a fear of fiberglass fumes, dust, noise pissing off your neighbours and getting you evicted, I recommend bringing your gear to an empty parking lot in early mornings to work... sure people may think you're crazy... or some sort of Al Qaeda operative with your respirator on, painting a strange box with some substance.. but at least it won't get you in sh*t. I found ways of doing this entire project (with the exception of minor steps, and the first soaking layer) in public places. Grinding is especially dusty. If you need a power outlet, check out public schools on weekends. Usually there's a power plug out there so you can use your grinder or rotary tool. When you paint, bring a book or something to do... it can be brutal waiting for paint to dry so you can transport your piece.