Fiberglass boxes require skill and patience, don't expect to get it done in one day. A custom audio shop would be much more suited to doing this. I've heard that the best box for a hatchback is the bandpass, but I can't say that from experience. (I have a sedan) Good luck on your endeavours, and remember make sure you like how it sounds, and screw all those who say otherwise. [thumb]
What type of box you want to use depends on what subs you have and what type of music you listen to. Bandpass boxes are great for making subs sound "punchier", so they are best for 10in-12in speakers playing mostly rock music with smacking drum beats (usually low-mid power rated subs go in bandpass boxes). A plain sealed box is less punchy, and is a good rock/rap mix with smacking drums and long deep bass notes (low-high power subs). A regular ported box is good for rap music with mostly long deep notes because the cone moves more freely (this isn't as responsive as the other two and tends to have worse sound quality, but it's also the loudest setup and uses less power to make higher volumes).
BTW: some subs can't play in "free air" or ported boxes and have to be in sealed or bandpass
I have a regular sealed inclosure because I switch up my music genres a lot, and it works out best for me. Most fiberglass setups are sealed inclosures.
If you want to build a custom fiberglass sub box, go to Lowes (or you local autoparts store...maybe), and get 2 things...1) a roll of fiberglass cloth, 2) a can of fiberglass resin/hardener. Now, I think the instructions are on the containers, but for the most part, I think it's just....lay down the cloth in your mold (like the spare tire well, if that's where you planned on putting your sub(s)), and start spreading the resin over the cloth. Give it time to harden, and somewhere in the hardening stage the combined materials are flexible, but hold their shape and can be hand molded to a certain extent (make sure you plan this out so the finished product is a sealed enclosure). Let it dry and give it a few more coats of resin/hardener giving proper drying time between coats. Sand and paint (if you want to).
If I'm wrong on any of this, someone please give more input.
I've done a 'glass enclosure in the spare tire well of my ZX3. It's a sealed enclosure. Mine is 3/4 glass and about a 1/4 MDF. The bottom and 4 sides are glass while the top baffle (and integrated amp enclosure) is made from MDF. I've also done another enclosure that used fiberglass as the facia to create a contoured surface, as well as two sets of fiberglass speaker enclosures for component speakers. This is absolutely something that you can do, it does not require any special knowlege, apart from what we can suggest in a couple of paragraphs.
When I did my enclosure, I used atleast one of the large 2L (half gallon) containers of resin, maybe another smaller one too, can't remember. You're gonna want to build it up until it's atleast a good half inch thick in the large flat areas. Any place that there's a contour, the same thickness is not required. I did mine at my work place, and used their scale to precisely measure the hardener - resin mixture, because I was a keener at first. Funny thing is that using their ratio, I used up about 2/3 of the resin when I finished the hardener (supplied with the resin). So, I'd have an extra bottle of hardener on hand. As for getting the mixture right, guestimation is all that's required. You're gonna be making a lot of batches, so after the first couple (hardening too fast, hardening too slow) you'll get the idea of how much hardener to use. [8D]
As for the mould, in the case of the spare tire well, cut open a large garbage bag, and lay it in the area (single thickness). Make sure there are no seams for resin to leak through. The garbage bags are nice becaus they're very stretchy (the good ones) to form to the shape, and you can peel them of the dried resin afterward. Much easier then trying to use wax or mould parting compound. Then paint some resin in the area you'll start with. Lay in some strips of glass (cloth is easier to work with, but more expensive than mat), and soak it thouroughly with resin. A dabbing action is much better than trying to spread it. I would suggest the cheapest brushes you can find, either bristle or foam, because it's pretty tough to clean the resin. I'd just count on tossing the brush after a batch or two of resin.
Building up the layers, it's best to build up smaller sections two or three layers at a time, rather than doing the entire area with one layer, then letting that dry and coming back to do subsequent layers. Once you get one piece of glass thouroughly soaked with resin, do the same with a few pieces around it, and then lay another layer over these, making sure to cover the joint of the previous layer with the new pieces. When you dab these pieces with resin to soak them, you'll barely need any more resin, as the excess from the previous layers will soak through into the new ones. Again, if there are no contours in the area, ie. a flat panel, the thicker the better. You'll see from working with it, fiberglass is very strong, but requires the distance between the top and bottom layers to gain its strength. This is how "honeycomb" panels work. A few layers of fiberglass on either side of the honeycomb provide the strength, while the honeycomb material simply spaces the two layers apart and ties them together. You can cheat this way too when doing large areas to save weight and time building thickness to get the strength you need. You can place strips of 1/4-3/8" particle board, across open areas once you have two or three good layers down, then put another few good layers over the strips. The strips should be about an inch wide, however long you need. Space them atleast a half inch apart, you need to make sure that you can get the top layers to curve down between the strips, and make a good bond with the bottom layers around the strips. High density foam (signbuilder's foam) will work very well too. Best way to judge how many layers is to lay a few, and let them cure, then pull it out and test it. It should'nt give any more than a panel of 3/4" MDF of the same shape. When you're happy with the strength, back into the mould and let it sit until it is COMPLETELY cured. Like silly putty, it will creep out of shape even after it seems dry. If it is a closed shape then don't worry about it.
I have never heard of people "working" the resin like clay or something and then letting it dry, I would treat it more like glue. The only difference being, that it will stay syropy (spelling?) for say 10-15 min. but once it kicks (as they say) it will start to turn to jello, and continue hardening very quickly. This "working" time when it stays runny varies with the amount of hardener in the resin.
Now if you're doing free-form shapes like kickpanels, or facias or stuff like that, it's another story. Easiest way to do that is to create the framework (wooden baffle for the speaker, and some sort of mounting system for the entire piece) and stretch spandex (or pantihose) over the structure. Then apply a coat of only resin (and hardener of course). Once that dries, it will provide a semi-rigid shape to apply further layers of resin and glass to, as above.
I hope that you find the info you were looking for, I'll be around if you have any other questions that were'nt answered above.
Good luck, and take some pics of the process, we'd all love to see them! [thumb]
Well put, I'm planning a fiberglass enclosure as well. Going to make a frame and go from there. I've done a bunch of work with fiberglass on boats and stuff. The garbage bag is a great idea, tin foil will work too