Car Audio Building the fiberglass subwoofer enclosure Bose style

I have always been a big fan of totally enclosed subwoofer setups. I think they produce a great sound and the best thing is that your speakers are hidden from view. In this article/tutorial I will outline the steps that we took to begin building a very large totally enclosed subwoofer unit for the eXtremeSuper project.

“Building it Bose Style” we will gain deeper bass sounds from the sub by channeling the subwoofer’s low bass tones through a maze of “tunnels” contained within the sub enclosure. This increase’s the subs low tone’s capabilities.

The subwoofer itself is a single Rockford Fosgate 12”. I plan to mount it inside the cabinet on the drivers side of the vehicle and have all of the internal venting “tunnels” on the passengers side and the main vent out through the top center of the subwoofer box.

I have built one of these before using a single JBL 6” subwoofer, and it rocked so hopefully with the larger speaker and the added volume (size) of the box we will get even better results. On to the building.

Supplies you will Need

· Cheap Paint brushes

· Masking tape

· Tinfoil

· Spray Adhesive

· Fiberglass Matting

· Fiberglass Resin

· Fiberglass Filler

· Few yards of Fleece material

· Plywood

· 1x1x10 wood rails

* A great place to find some of these supplies is at any Dollar Store. Most likely you will be able to find: Masking Tape, Tin Foil, Rubber Gloves, Paint brushes all for $1.

Begin by using a cutting wheel to remove any useless brackets that may be in the way. Clean up the area to be used as the form for the box.

Using Masking tape, Cover the entire area where the fiberglass would touch the vehicle. The tape keeps the fiberglass resin from sticking to the metal. Fiberglass resin is nasty stuff, it will stick to anything, and that includes you.

Using 3M adhesive spray glue spray the layers of tape and lay down Tin Foil. The tin foil will adhere to the tape using the spray glue with no problems. This is just an added layer of protection from the fiberglass resin. In case there was a hole in your tape, the tin foil would cover it and no resin would get on the vehicle.

Cut up your fiberglass matting into strips about 2inches wide and about 6 inches long. Once completed mix a cup of fiberglass resin and hardener.

Lay down a strip of the fiberglass matting, start in the corners first (for strength) Use a 2” or 3” wide cheap paintbrushes (get a bunch of these) soak it with resin and apply the resin to the strip. It may be a bit tricky at first until you get the hang of how the resin reacts with the fiberglass mat, but after a few strips you will get the hang of it. To make your life easier when fiberglassing, use a can of WD40 Lubricant spray, when your rubber gloves become sticky spray on some WD40. Do this how ever many times you need (it helps big-time).

After the first strip, just keep piecing them all together, making sure that each piece overlaps just a bit until you have covered the entire area. Pieces can crossover each other.

Once you have them all in place and thoroughly soaked with resin, it will need to harden. You can expect it to take anywhere from 24 hours to 3 days, depending on how you mixed the hardener with the resin (Smaller amount of hardener, longer the cure time. More hardener the faster the cure time).

Once it has fully hardened you can grab the edges an “Break it loose” from the tin foil and the tape. You should end up with an exact shell of your sub box area. At this time though keep the shell in place until after the next step. If you remove the shell at this time it could possibly warp and not fit back in the area correctly.

Using a bandsaw or jigsaw cut up a 1x1x10 piece of wood. Cut them in sort of a pyramid type shape. These are going to be used for a structure ridge along the top of our box. Use a cutting wheel to trim the really rough pieces of fiberglass from the top of the shell. To secure the ridge blocks use a hot glue gun to adhere them to the ridge line of the shell. The pyramid shape allows you to turn the blocks and achieve a better “Gap Fill” between each of the blocks and allows you to place them around the curves of the shell.

Once the fiberglass matting has completely cured and you have “Broken it loose” the next step is to “Thicken it up a bit”. We will do this by applying 1 or 2 coats of Fiberglass Body filler over the entire inside area of the shell. This will add strength to the shell and help avoid cracking of the fiberglass.

(Above) This is the initial layer of fiberglass mat all dry without the edge blocks around the top.

My goal is to apply it quite generously over the entire inside of the enclosure and try and maintain an even thickness. Mix up the fiberglass filler on some cardboard, and go to town. Spread it all over the inside of the enclosure, make sure to go a little heavy in the corners for additional strength.

Coat the entire inside of the enclosure with the fiberglass filler and let it cure. Make sure to fill in the gaps between the wood blocks you glued around the ridgeline in the previous step.