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This is the second fiberglass box I have built, and I must say, it came out better than the last. I'm going to give you guys a quick run down on the build since there are tons of other DIY's online for fiberglass box builds, but this will be specific to mine and the 12 EX Civic.Supplies needed:
  1. 1 Gallon of Fiberglass resin. I used 3m brand from Home Depot. It came with two bottles of hardener under the cap, so do not buy hardener
  2. Box of disposable gloves. I just used the blue nitrile non-latex gloves and they work fine. No need for the fancy gloves, its too hard to keep them usable.
  3. Roll of blue painters tape
  4. About 10 cheap, disposable paint brushes
  5. 2-3 packs of fiberglass cloth. I used the big weave, but the tight weave works just the same
  6. 2-3 paint mixing cups with measurements in ounces
  7. 1 yard of fleece
  8. Tube of silicone
  9. Can of high quality spray adhesive
  10. Good respirator mask. This stuff is very, very odorous and can make you light headed, even with plenty of ventilation.
  11. Good scissors to cut fiberglass weave into small pieces
  12. Dremel with grinding wheel
  13. 1 small sheet of MDF board for the speaker mount
First step is to tape of the area of the trunk you want to conform to. I use the good quality blue painters tape because you do not want this stuff to get on your carpet. It is not going to come off if it does. Tape in a criss cross fashion as to cover every inch of carpet you are shaping to. Also extend the tape several inches beyond the shape of the box you are making. I also laid down some painters paper in the trunk just to prevent any accidents. I do not have any pics of this step.Next, cut your fiberglass weave into small pieces, around 3x3" squares are what I used.Mix 8 ounces of fiberglass resin with the hardener. The 3m calls for 10 drops per ounce. The more drops you add the faster the resin hardens, so don't get carried away. Once the resin starts hardening you can't use it the way you need to. With your gloves and mask on, it's time to start painting the resin mixture onto the painters tape you laid down. It will be sticky like honey, so spread it all around. Now you will start sticking the fiberglass squares onto the resin making sure to cover all of the area your box will cover. Don't worry about the edges being nice or beyond your box as you will have to trim and clean it up anyway. Cover all of the laid fiberglass squares with more resin until the cloth looks soaked in the stuff. The fiberglass will turn from white to yellow once it has soaked up the resin. Try to get as many air bubbles out with your paint brush as you can. Now, add more fiberglass squares on top of the previous layer of fiberglass squares and coat with another layer of resin. Repeat this process about 4-5 times to get good coverage. You may have to mix more resin to complete the layers. You can always mix less resin if you don't need another 8 ounces. Do not leave any resin in the painters cup as it will just harden.You can go ahead and throw your gloves and brushes away since you have the cheap ones and plenty more to use. Time to patiently wait for this layer to dry. It will take about 4-5 hours to cure, so find something to do. This is what it will look like after drying.



Now you can remove the shell from your trunk to continue the rest of your work out of the trunk. It is much easier to paint on the resin and layer the fiberglass with the shell out of the trunk. Go ahead and mix another batch of resin, I always start with 8 ounces, and have some fiberglass squares ready to go. Paint on a coat of the mixed resin and lay down a layer of fiberglass squares. Repeat this process 2-3 more times, until you are comfortable with the strength and coverage.


Once that layer has dried, put the shell back in your trunk and mark off the edge of your box using a sharpie. I just freehanded mine being sure to include the strongest edge of the shell all the way around. Once you have marked the edge, cut off the rough edge with a dremel. I used a plastic cutting wheel for mine, but you may cut it with any means you have available. Be sure to wear a mask and glasses as you DO NOT want fiberglass dust in your eyes and lungs. Put the shell back in to verify the fitment. You can also use water to measure the volume of your box to make sure you're within the specifications of your sub. I was within the specs for my Rockford Fosgate P2 10" sub based on volume. You can can add volume by placing a few or the upcoming outline/support pieces on top of eachother or decrease the volume by trimming the rear of the box down some. I wouldn't worry about have too much volume though because you can just easily add some decron foam inside the box if needed.



The next step is creating the front of the box. Some people using a floating ring method to have a more cone shaped front, but I wanted the front of mine flat. I first laid my shell down on the MDF and traced the outline of the flat 2 edges. I then free handed the same line about 3 inches parallel to the first outline. Cut this piece out and screw it flush to the inside of the shell to give yourself a foundation to work with. Use small screws and be sure to drill pilot holes to make it easier to screw through the fiberglass. Use some silicone to seal the gap between the box and wood.



Now that you have a base of the front to work with, you can cut out the front of the box in the shape you want. I wanted it to be flat and just conform to the box shape, but you could get creative with a slightly different shape if you wanted.



You will need to get an idea if the rear of the speaker will fit in the box using just the one cutout for the front of the box. The depth of mine required me to cut a duplicate of the front to lift the speaker further away from the back of the box. If you need another, simply trace the first one and cut out a second just like it. You can either use wood glue or silicone to attach and seal the front plate to the outline/support board you attached to the inside of the box. Screw the front of the box to the outline/support once you have it lined up with the back of your box. Do not worry about the big gap on the top for now, it will be covered with fiberglass.

At this point, the bottom and left side of the box are closed and sealed with the front plate flush against the fiberglass back. I attached the second front plate to the first with silicone and screws so I would have enough space between the rear of the box and the speaker when mounted. Use either a template or find the diameter of your sub and position the hole on the front plate to be cut out. I was able to use the styrofoam packing of mine as the template. I suggest you use some clamps while working with the wood to keep everything in place.




You are now able to drop your speaker into the box and check for fitment!

If the speaker fits fine and you do not see any problems, it's time to begin with the front of the box. Also, be sure to check the clearance of the box with your trunk arms. It wasn't even close with my build.

Time for more fiberglass!! First, cut a piece of fleece thats large enough to wrap from the front of the box to the back and right side. You only want to use one piece of fleece for this part. Do not worry about having alot of excess fleece between your connection as it will be trimmed off later. Staple the fleece to the front of the box and make sure it is tight with no wrinkles. Now pull the fleece around to the back of the box and spray the top of the fiberglass back with the spray adhesive. Attach the fleece to the back of the box all the way around, again, without wrinkles. The fleece can be stretched and pulled to where there are no wrinkles. You can now put the box back in to check for fitment!



This will be the shape of your box! Time to get some resin mixed up. 8 ounces of the resin mix will be too much for this part, so mix about 6 ounces of resin. After getting your mask and gloves back out, coat the fleece cloth in the resin mix. Get it nice and soaked so it appears yellowish and there is no white fleece showing. You are going to just apply the resin and let it cure. DO NOT apply any fiberglass on this step as the weight will deform the flowing shape of your fleece and box.




Once the resin on the fleece has cured, you can trim off the excess fleece around the front and back of the box. It's time to start applying fiberglass on the fleece. Mix up 8 ounces of the resin mix and have your fiberglass precut and ready to use. Paint on a coating of resin and then lay the fiberglass on top. Coat the tope of the fiberglass and lay another layer of fiberglass on top of that and repeat one more time. This will give you about the same strength and thickness as the rest of the box since it includes the fleece as the base. Let the resin cure. You now have a fiberglass enclosure with an MDF front!



It's now time to clean and seal it up. Use your grinding wheel on your dremel to remove any stray pieces of fiberglass and resin bumps. You don't have to worry to much about the back of the box, but you still want to get anything big off to prevent fitment issues or future cuts on your hands. The top and front of the box need to be grinded down pretty smooth. I used carpet, so I did not have to have a nicely sanded down surface, just smooth. If you're going to use vinyl, you will have to use sandpaper to sand down the front and top of the box or any bump will show through. I suggest just sticking with carpet. Take your silicone and run it across all of the seams inside the box to ensure it is sealed.



You can find matching carpet at a car audio shop or a fabric store. You only need a yard and you'll have plenty left over. Drape the carpet over the front and wrap it around the box giving yourself about 6 inches beyond the visible sides of the box. Spray the front of the box with adhesive and lay the carpet smoothly on the MDF. Don't worry about the speaker hole, you can cut that out later. Place the box with the front down to allow the adhesive to stick to the carpet. You can now pull the carpet around the back of the box. You can only do one side at a time. Spray the first few inches of the back of the box you are working on with the spray adhesive and pull the carpet tightly and attach it to the box. Once the adhesive has cured, cut a slit down the corner and repeat the same steps until you have finished all 4 sides. You can then trim the excess carpet and cut out the speaker hole using a razer blade.



The last step before mounting the speaker is to drill a large enough off in the back/bottom of the box for your speaker wire to pass through. Give yourself enough wire in the box to work with and then seal the hole with plenty of silicone. Time to mount your speaker and enjoy your custom built fiberglass box!

****Please see addition to DIY 10 posts below about mounting.*****



If any Houston guys want some help, let me know and I'd be happy to meet up and lend a hand!
 

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I too have thought about this route, that way I could get the bass back that I am looking for, but I am worried about working with resin and fiberglass. I have never done this before. I have seen this before. Great write up by the way.

Let us know how you rank it on a scale of 1-10 with no experience working with fiberglass and resin. What was the final cost of the box?
 

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Discussion Starter · #7 ·
I too have thought about this route, that way I could get the bass back that I am looking for, but I am worried about working with resin and fiberglass. I have never done this before. I have seen this before. Great write up by the way.

Let us know how you rank it on a scale of 1-10 with no experience working with fiberglass and resin. What was the final cost of the box?
It's really not hard, but give yourself at minimum 4 days to work on it. There is alot of down time because the resin has to cure before moving on to the next step. From 1-10 with no previous fiberglass experience, I would rate it a 5.

The box cost me about $150 to build. All of my supplies were bought at Home Depot, except the carpet. The car audio shop quoted me close to $500 to do the same thing, so I think I did pretty good!
 

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It's really not hard, but give yourself at minimum 4 days to work on it. There is alot of down time because the resin has to cure before moving on to the next step. From 1-10 with no previous fiberglass experience, I would rate it a 5.

The box cost me about $150 to build. All of my supplies were bought at Home Depot, except the carpet. The car audio shop quoted me close to $500 to do the same thing, so I think I did pretty good!
Sweet, write up! Thanks for the time and effort.

What size sub did you use?
How much does it weight?
Do you have any idea what the cubic footage is of your box?
and of course...
How does it sound?!
 

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Discussion Starter · #11 ·
Just wanted to add that the box has to be mounted or it will roll around. I would do this step before mounting the speaker in the box. There is a piece of metal bracing right behind the carpet where the box goes. It has two perfect size holes to choose from to bolt the box to the trunk.

Mount a 4" bolt to the trunk with either of the two holes and cut a slit for it to pass through the carpet. You will need to leave the nut on so a second nut will be needed to secure the box. Put some nail polish on the end of the bolt and slide the box into place and the bolt will leave a marking for the hole in the box.

Drill the hole in the box with a small bit and work incrementally up to the diameter of your bolt. The bolt should fit through the hole with just a little bit of wiggle room. Use a foam washer then a flat washer before the nut to keep the hole sealed. Also, use some loctite to be sure the nut is secure and doesn't back off. Now install the speaker into the box and you're ready to hit the corners with some thump in the trunk!

I am loving my setup! The Rockford Fosgate amp and sub is delivering EXACTLY what I wanted. Deep, loud bass on the inside and very little on the outside. I have no rattles coming from the inside or out, so that was just a bonus!!


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