There’s many threads out there on custom fiberglass enclosures, but I figured the more the merrier, right? I know that during my creation, I was always looking for another opinion from another source, just so I could be sure of what I was doing. Well, I’ll talk about what worked for me, what didn’t work for me, what to do, and what not to do in the following DIY.

Let me start off by listing my sources:
Fiberglass for Newbies
DIY: Fiberglass Speaker Enclosures (by BobTheEskimo)
DIY: lil benny's custom fiberglass enclosure (by... lil benny)
I highly recommend you read their DIYs too, as the more information and knowledge you have, the better your enclosure will be.

Scroll down for an exhilerating journey of excitement and adventure...

 

Okay. Make sure to get all your materials from the start. I was always missing one thing or another, and so I had to keep running to the hardware store. Don’t do that, it’s a pain. Most everything listed below I got at the local Home Depot, unless otherwise noted:

• 2 rolls of 2 inch blue painter’s tape (this is used to mask up the inside of your car – it will be easier to remove than regular yellowish masking tape)
• A bunch of trash bags (to cover the rest of your trunk so you don’t get fiberglass resin all over it… very important)
• 5-10 paintbrushes (I got relatively cheap “economy brushes” – they worked pretty well. Don’t use foam brushes! You need regular ones with bristles. As for width, I bought a variety of sizes, but keep it around 1.5 inches - those were the most useful)
• 1 pack of fiberglass mat (this is the fuzzy inter-woven stranded fiberglass stuff used to reinforce your enclosure)
• 1 pack of fiberglass cloth (this the white cloth also used to bolster your shell)
• Lots of rubber gloves (I went through many, many pairs of gloves. I recommend you get a big box of them, not just the 10 pack I have shown in the picture. You will get fiberglass on them, and they will get sticky, and you will have to keep putting on new ones)
• A good respirator (I bought the Kimberly-Clark R95 respirator in the picture from home depot – I highly recommend it, as the little exhalation valve made life a lot better than with just the regular ones. You WILL need one of these, as the fumes are quite potent)
• 1-2 gallons of Fiberglass resin (the amount you need will depend on how efficiently you work and how much you waste. I ended up needing 2 gallons, and I think the enclosure wouldn’t be strong enough with only one.)
• 1 extra tube of resin hardener (I found that the 2 tubes included with each gallon of resin weren’t quite enough)
• Acetone (I forgot to get this, so I ended up using isopropyl alcohol which works almost as well. You need about a quart…? It depends on how much you want to re-use your paintbrushes)
• 3-4 small paint buckets (I highly recommend the clear ones with the measurements down the side)
• A bunch of paint mixing sticks. (just ask the guy behind the paint counter nicely, and don’t forget to say please. He gave me a handful of them for free)
• Stretchy fabric (I got mine from a new England franchise called jo-ann’s fabrics. Just go to your local fabric store and ask for their most stretchy fabric. Mine is like a black nylon sort of fabric, and is very stretchy like stockings)
• 3M High Strength “90” Spray Adhesive (I recommend “90”, it is very good for tacking the fabric to the shell)
• Canola oil (any sort of vegetable oil will do. I had a cool cooking gadget that pressurizes and sprays whatever oil you put into it as a fine mist – it was very helpful. Im sure Pam original would work, and that obviously sprays too)
• 1 quart of fiberglass filler (also called duraglass or bondoglass or something. It’s a thick green fiberglass paste, unlike the thinner, yellowish resin)
• ˝ inch dowels (about 5 feet worth? I used less, but they’re cheap, so get enough)
• MDF subwoofer ring (I had the local Tweeter make mine for 30 bucks, but if you have the necessary power tools, there are good instructions at Fiberglass For Newbies.)
• Sharpie permanent markers
• Carpeting (this was hard for me to find. The right color carpeting at home depot was way too thick to work with. You might have to order it from a car audio specialist site, such as crutchfield. Personally, I had Tweeter carpet mine for 25 dollars.)
• And most importantly, a loud boombox with your ipod or a bunch of good CDs (and a fan if it’s a hot summer day)

All in all, I think the materials cost me around 150 dollars.

Some Tools:

• Scissors
• Utility knife
• Vaccum
• Paper Towels
• Hot glue gun
• Dremel with fiberglass cutoff wheel and sanding bits (this was very helpful)

 

Okay, the first thing you need to do is mask up the inside of your car with the blue painters tape. This step needs to be done very meticulously in order to protect your trunk. Get used to bending over into the trunk - you'll be doing this a lot. Luckily, I happen to be only 5'9" and still pretty agile cause I'm a kid... I actually lied down in the trunk for about 3/4ths of this process. Made it much easier.

Start with the corners. Have a few pieces of tape covering each “sharp” corner, going at least 2 inch out. Then, start with the bigger, broader sections. I highly recommend doing each in longish, parallel, overlapping tape lengths. Also, make sure you go well past what you are going to fiberglass. Then, do the corners and adjoining edges again.

At this point, you should not be able to see any carpet spots. If you do, cover them up. Now, go over all your masking with another full layer, but have the tape on this layer running perpendicular-ly to the first layer’s tape. After this layer, you should have a very clean-looking masking job. In my pictures, it looks as if my trunk is actually blue.

Your tape should be very cleanly adhered, with no big wrinkles or anything like that. Make sure you didn't miss a single spot!!! This means you really have to get your head in there and look up at all the overhanging spots you might not have seen. Also, tape past the edges of the carpeting, even up onto the metal.

Note: To help with lighting, the whole time i was working in my trunk, especially later with the fiberglass, i put a flexible-neck desk lamp on the other side of my trunk. I recommend this.

 

Make an approximate outline with the sharpie of how big you want your enclosure to be. When you actually start fiberglassing, go past this line. You will later trim it.


Next, cover your whole trunk with garbage bags to protect it. You don’t want this stuff getting on your paint! The picture below shows a decent masking job, but make sure you also cover the top rubber thing that contacts the trunklid to seal out water when it rains. When I was fiberglassing, I kept unconsciously reaching for it to lean on while I painted. Luckily I didn’t do any damage before I realized and masked it up.

 

Note: Before you start with fiberglass, put on a long sleeve shirt that you don’t care about! This stuff is not fun to have to peel off your skin or pull out of your arm hair.

Sadly, I became too engrossed in my creation to take any pictures of it during the fiberglassing process. Here’s what I did though: Before your first layer, spray a light layer of vegetable oil on the painters tape. This will help to make the tape easier to remove once it becomes time for that. For your first layer, just paint the whole area with the fiberglass resin and don’t bother with any fiberglass mat or cloth yet. I tried to use those on my first layer, and it was nearly impossible to get them to stick. Then I had many big bubbles and wrinkle I had to later sand out. Instead, just don’t use either on your first coat. For the rest of the layers, alternate between using the mat and the cloth. The basic steps for each layer are as follows:

• Put on gloves and mask
• Pour about a fourth of a quart of the fiberglass resin into your mixing bucket.
• Squeeze about 10 milliliters of hardener into the resin and mix thoroughly. You will have about 15 minutes to work before it hardens. The more hardener the use, the quicker it will harden. Experiment with different amounts and you’ll get the hang of it.
• Dip brush in resin and paint desired area
• Then, tear or cut a portion of the mat or cloth to the size desired, and apply to the wet area. Do this with your hands, and kind of lightly pat the cloth or mat onto the wet surface. For the first few tries, it will be reluctant to stay, but once you get the hang of it, it becomes easy. Once your mat or cloth is sticking flat and absorbing the resin (becoming clear), dip your brush in the resin and lightly paint the outside of the mat or cloth. Use a kind of dabbing motion in order to get more resin into the mat or cloth. You want the mat or cloth to become fully saturated with resin – you’ll know this happened when it has turned mostly clear.
• Repeat the painting-matting-painting on each desired area until you run out of resin or it hardens beyond usage.
  If you plan on being able to use your brush again, try to wipe all the resin out of it onto some paper towels, pour some acetone onto the brush, and clean it out again. Then, leave it lying in a shallow container of acetone.

This process is tricky when you’re just starting, so I recommend you take a look at the links above and read the other people’s descriptions of how to do it.

 

Keep a few things in mind: fiberglass is stronger in curving areas than wide open, flat areas. Also, you only want to do this in your trunk until it is strong enough to take it out. Once you can take it out of your trunk, life becomes a lot easier because then you can work on it in a more comfortable position, and more importantly, you will no longer have to fight gravity when doing the walls and upside-down parts. You can work on one portion of the enclosure at a time, and turn the enclosure in such a way that that side is on the bottom.

Here’s some tips on getting it out of the trunk:

• First, let it dry completely. Give it a few hours to be sure.
• Slowly peel the masking tape that sticks out beyond the fiberglass from the carpet. Once it is peeled to the start of the fiberglass, you might have some of the fiberglass crack off and break. This is ok if you painted well beyond your line.
• Anyway, try to ease the side of your enclosure from the trunk. Play around and you’ll see what I mean. Slowly the tape will start to peel away from the carpet and the enclosure will come free.
• Mind that you’re trying to take the enclosure with the tape still on it from the trunk – the tape will stick more strongly to the enclosure than the trunk – that’s good. You aren’t trying to peel the tape off the enclosure yet.

Note: look how lumpy and un-even my fiberglassing was. This is because i tried to use mat on my first layer, and it all kind of fell half-off then hardened... before i went any further, i made sure to sand down all my bad lumps and bubbles so that it was all very smooth before i did my next layers.

Note: at any point in time, feel free to sand away any big bubbles or anything like that. You don’t want any bubbles in your fiberglass. My dremel sanding bits worked miracles for that. Also, you especially don’t want to breathe the white fiberglass dust!!! Finally, if you do sand, make sure you use a damp cloth to clean the entire enclosure before your next coat so that the fiberglass sticks better to itself.

 

Once the enclosure is out, do more layers until the whole thing is around ˝ inch thick. More importantly, you don’t want to be able to bend (or break) the shell.

Once you’re happy with the thickness and strength, put it back into the trunk. It should still fit snugly into the depression because you haven’t done anything to the outside. At this point, re-draw your lines with the permanent marker. When you take it out again, you can finally peel the tape off the enclosure. This might not happen so easily, but stick with it. You can always lightly sand parts of it if you need to. Mind that you will rarely ever see the back of the shell unless you take it out of the trunk. Also, you can always paint the shell or something, but i didnt bother. I was able to remove all the tape except for a few little scraps embedded in the fiberglass here and there.

In my picture, you can see my sub ring - thats because i didnt have any pictures of the tape peeled off until after i mounted it.

 

Using the fiberglass cutoff disc on your dremel, trim the enclosure down to size. I made sure to have long, smooth, curving cuts. You don’t want any dramatic or sharp changes in direction. Also, leave it a little bigger than you may want. You will probably do some trimming after you mount the MDF ring like me.

Then, once this is trimmed, it is time for the MDF sub ring. Unlike most, the one made for me just had a plastic ring around the outside. You can have it like this, but I recommend you make it like the instructions on Fiberglass for Newbies. Having a thicker outer ring would make life a lot easier. Anyway, mounting this ring in the right place can be a pain. Keep in mind that if you want the final enclosure to have the sub ring sticking out a little like most do, then the plane made by the face of the MDF ring has to go beyond all edges of the enclosure. I tested this with a meter stick – I laid it down on the MDF ring, and rotated it, making sure it cleared all the edges of the shell. I thought about this and kept it in mind, but I actually left some points sticking out past my plane and trimmed them once I mounted the sub ring.

With all that in mind, here’s how I positioned my MDF ring: I tied pieces of string around it, and then I ran them to the back of my enclosure and glued them in place. The picture will probably explain this better than my words. Important: make sure your sub fits! Have someone help you gently lower your sub into the ring to make sure it can be seated firmly in that position without the voice coils or whatever on the back of the ring hitting the enclosure.

Note about MDF ring: The MDF rings in the "fiberglass for newbies" guide and in my DIY are called "recessed MDF rings" because the subwoofer sits in the recessed area. i HIGHLY recommend making a recessed MDF ring for this enclosure, as it would look pretty bad with the edge of the subwoofer just hanging out there.

 

Once the ring is positioned how you like, start cutting dowels to the proper lengths, and have them running from the back of your MDF ring to strong points on the enclosure. Make sure you mount this all very strongly, as this is what provides support for your subwoofer. Keep in mind that you will probably have to do a lot of beveling in order to have the ends of the dowels sit flat against whatever surface. For now, use a little bit of hot glue to mount the dowels in place. Now all your dowels should be in place, and your sub ring should be mounted relatively securely, but no where near strong enough to hold the subwoofer.

I actually hot-glued the dowels only to the fiberglass base first, so you can see tem all sticking out without the MDF ring mounted yet. Notice the surplus of dowels on the bottom, and also the two facing kind of backwards - these are important because they will be holding most of the weight of the sub

The next step is to fiberglass the dowels in place. Make big strong bases for them, and don’t forget to use fiberglass mat or cloth. I made a mess of the inside of my enclosure here, but as long as they’re mounted securely, it doesn’t matter because no one will see the inside once you’re done.

More pics of mounted ring and in the trunk are on next post.

 

Now, get the fabric and stretch it over the whole thing. You want to be able to see the pronounced ring sticking out past the edges of the enclosure. At this point, I trimmed my enclosure back so that I had satisfactory sweeping curves leading up to the MDF ring.

Okay, get the spray adhesive and follow the directions on the can. Though it says both surfaces, you don’t actually need to pre-spray the fabric. Do one side and let it dry. Then do the opposite side, and let it dry. Then do the other two. Once done with this step, you should have a tightly stretched fabric over the whole front of the enclosure. Read fiberglassing for newbies for extra info on these steps. At this point, you can take the utility knife and cut all the extra material. Personally, I cut it so there was 2 inches past the edge of the enclosure.

note that the last attached pic is from the last post.

 

Now, take out the fiberglass again, and fiberglass the fabric. On the first coat, don’t use any sort of mat or cloth. Cover the whole front, including the center of the ring, which you will later just cut out. The reason for this is because you don’t want the part surrounding the ring to crack if you by accident pushed the fabric in the middle and it was stretchy.

On the next coat, still don’t use mat or cloth. Make sure to get the edges of the enclosure and the over-hanging fabric on this one. Now you will have a lightly-fiberglassed cloth stretched over the whole thing. I don’t recommend you test it’s strength yet, because you’ll see that if you do, it will ruin the integrity of the first coat as it develops lots of little cracks when you push on it.

Anyway, from here on, continue to coat the fabric, and don’t forget to use mat or cloth. You don’t need to coat the center of the ring anymore though; I just recommend one or two coats at the start. Try to be very methodical though, as you don’t want any wrinkles here! Don’t worry too much about minor imperfections though, as we will sand it later. Also, be sure to add plenty of reinforcement around the edge of the ring. I cut 1 inch strips of both mat and clothe and just went around the circle to make sure that was strong.

Once the whole thing is built up strongly, test the flat areas for strength. When you push down, it shouldn’t bend in. Now, you need to cut out the center. I used scissors and a utility knife for the center of the circle, which didn’t have a lot of fiberglass. As you get towards the edge of the ring though, I had to switch over to my dremel sanding wheel. Start to sand down the overhanging fanbric until you get near the ring. Be careful when you get close to the edge, because you don’t want to over sand, especially if your outer ring is as thin as mine.

Notice how my fiberglassed fabric goes right up to the ring, and juts just a little bit over. This is for strength purposes because my outer ring is so thing, and also so that when i carpet it, i can have the carpet hang over the edge, and tucked under the sub.

 

You should now have an almost completed enclosure. The next step is important though. Take the thicker duraglass or fiberglass filler, and follow the directions on the can about how to mix it with the hardener. Then, with rubber gloves, scoop it onto your finger tips and pack in firmly on the inside of the enclosure where the fabric meets the MDF ring. This is necessary to ensure a good seal.

After that, you can drill a small hole in the back of the enclosure for the speaker wires. After running those, make sure you seal the hole with plenty of fiberglass (the fiberglass filler would seem like a better idea, but didn’t work as well for me… I just glopped on some resin and mat).

Next, drill pilot holes in the MDF ring so that you can mount the sub in the position you want. If you just screw right into it without drilling first, you could crack it. Just make sure that the holes you drill are smaller than your screws. Finally, you can carpet the whole thing using the 3M “90” spray adhesive or whatever. I had Tweeter carpet mine, so I can’t help you much with that one. Finish the wiring, screw in the sub, and you’re done! Congratulations! Hopefully this DIY helped you out – but if you have any questions, feel free to PM me.

 

Oh, almost forgot the most important thing: you’re all probably asking, “well… how does it sound?!?!”

The answer: This enclosure sounds GREAT! With a JL 12w3v2 sub, it produces really clean, tight bass. If I turn up the gains, it can get plenty loud as well.

I measured the size with packaging peanuts to be approximately 1.2 cubic feet, which is very close to the recommended size (1.5 cubic feet I think). Also, because of the way fiberglass acts, the sub actually “thinks” it’s in a bigger box, like around 1.4 cubic feet.

I highly recommend this DIY as it was a whole lot of fun, and it’s great to have a good sounding box that doesn’t take up so much room in our small trunk. All your friends will be amazed with it, and it’s a good experience working with the fiberglass. Have fun!

(you can post now...)

 

I just about to install a box I got off ebay it faces down and its against the backseats so i dont know how its gonna sound if it doesnt work out ill be sure using this DIY for my box
[B]
Hell I might just do it any way it looks great are you doing boths sides are just one.

 

So far only one side... but i think i'm addicted to my bass, it complements the music so incredibly well.... before i know it, i might just have a left-hand enclosure too...

have fun with your enclosure though, and let me know if you try this one out...

also, keep your eyes open for my next DIYs... i documented my whole audio install, so within the next week youll see me running my power cables, custom mounting my amp, tapping into the signals and everything else

 

This is a great DIY--- You layed out all the steps very nicely. This will really come in handy when I get time to free up some trunk space by making my own box because right now my audio system takes up the whole trunk! thanks again,
Will

 

Do you think it would be possible to squeeze 2.0 cubic feet out of one with a 3" port tube 14" inches deep?

 

how does this placement work with the sound? I know its a very pretty, convenient location but I have to wonder how this affects sound quality

 

all the guides i've read (car audio, home theater, anything) say that placement and orientation of subwoofers are of little concern.

I'm sure it might sound a little better if it was somehow facing the passenger area, but I truly don't think it would be a noticeable difference

 

1145climber, thanks for this diy on the fiberglass sub box. I have wanted to do that but to scared to mess with it. Well this weekend into the wee hours of the night i did it! I have not gotten it carpeted yet but it is so awesome to be able to do this myself. I will have some pics up soon if you want to see. I made mine a little larger (trail and error i think). Anyway thanks again!
Lurch634

 

Not done, but here is where I am at now.

 

Finally done! it took me about 15 hours total. I am very happy with the turn out. now I am working on my Amp rack!!

 

I'm like a year late, but this is an awsome DIY! Not sure if I'll be able to fit my sub... I have a 15"...

 

Me too, but I'm trying it anyway. I have two 10s so I'm opting for both sides. I'm wondering how to figure out the volume while you're making it though, as mine only needs about .65 cu. ft. each.

 

Nice DIY! I was always wondering of how to work with fiberglass! Now that I see its not that hard I might experiment with fiberglass in General! Thanks! this really helped me in a time of wonder! I have a 10inch Clif Designs Competition1100watt woofer with 1100 watt amp and I am only using 1.0 cubic feet of space in my zenclosure box. So yeah. The looks of it, it seems like its enough volume for your 10. My singel Ten is greater than most single 12"s.