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816 Posts
Discussion Starter · #1 · (Edited)
So, Here is a DIY guide to making your own Fiberglass Sub-woofer Enclosures. These are 12" ones that I made. Enjoy!!

Currently, I only have my progress on my Facebook page, but I will edit this thread and complete it when I'm all done. In the mean time, check out where I am currently at:

Ok, So now that I'm all done, I figured I'd do a write up on this. I know there are one or two others out there, but hey, this is what I choose to do with my time. Here we go.

This isn't necessarily a cheap project, but it's a hellofa lot cheaper than paying an audio garage to build them for you. I spent a little over $200 total.

Materials List: (Home Depot)
Resin (I used 3M Resin, about 2 gallons of it total) - $35 a gallon
Fiberglass Mat and/or cloth (I used 1 package per layer for both boxes, about 8 packages) - 7$ a package
Liquid hardener - 2 bottles come with each gallon of the 3M resin
Paint mixing cups - $1 each (I got 4, explain why later)
20+ paintbrushes, 1.5" - $15 for a package of 20
Latex gloves, box - $8
Masking Tape, get at least 3 rolls - $depends
Aluminum foil, 1 box - $3
Plastic drape - $2
Safety Glasses - $-
Respirator - $30
Hot Glue Gun - $5 Walmart
Glue Sticks - $3 Walmart
Fleece - I used reminants at walmart, %20 off. Don't remember the exact size, but I had plenty. Probably spend $15 total for all fleece
MDF or MDF rings - 4x8 sheet $28 at Lowes
Wooden Dowels - Made my own from scrap wood
Speaker Terminals - $4 local audio store
Dynamat - $varies
PolyFill - $3 /16oz - Walmart

For tools, you can use a lot of different items. I used:
Hot glue gun
Hole cutting drill bits and regular bits
Air powered sander

This is what I started with, Two Pioneer TS-W307D2 Subs in an ungodly heavy MDF box.

So, there's just a little prep work to be done.
Obviously you want to remove everything from your hatch. Also, you will want to remove the plastic clips from the rear and anything else in the way. You will need to allow 2-3 days of time that you will be actually working in the car.

When you start taping, take your time and make sure you are really getting the contour of the corner. You can get away with doing it half ass, but my boxes really stick in place because of all the minor detailing in it's creation. (Also, you may want to shut off your hatch light - just flip the hammer in the up position like if you had closed it)

It helps to be well :pimp

You will definitely want to make sure to over tape the are you are working on, you will be trimming it down later, right now, you don't care the shape it will ultimately have.

The next step is optional, and even though it takes a bit of time, it makes your life a lot easier when you take the molds out of the car.

Taking foil, contour it over the tape, and just secure it in place with smaller strips of tape. Like I said, kind of a PITA, but worth it to me

After you are all taped and foiled, take some plastic and tape off the rest of the hatch. Getting resin on anything other than your project is a serious pain, its very hard to clean off, even when still wet.

This is the Resin I used. Home Depot has all the fiberglass materials.

You can use either Fiberglass Mat or Cloth, which ever you prefer or both. I used Cloth on my first layer because it is soft and contours easily, then I used mat on the following two layers because of it's strength and rigidity.

This what they look like up close:

I cut both the Cloth and Mat into squares about this big. You may want to do this outside, because when you cut cloth and especially mat, the tiny pieces get everywhere.

:stop: This is also a good time to mention that you DO want to be wearing your respirator when you cut the fiberglass Mat OR Cloth if you are in your garage / indoors. Under a bright light, you can see all the airborne fiberglass particles and you do NOT want to breathe that. Also, to avoid getting fiber glass embedded in your skin (which sucks for like, two days) long sleeve shirts and gloves are recommended for the entire project, as well as Safety glasses. Moving on...

Now you are ready for the first coat of fiberglass. Mixing the resin and hardener is kind of a pain, and you do want to make sure to mix it really well. According to the directions, it's supposed to be 14 drops of hardener for every ounce of resin. I went with more like 10. That gives you about 15 minutes of working time.
I mixed about 10oz at a time, per layer, per side.

The technique for applying the resin and mat that I used, was to coat the area with a layer of resin, then lay the mat or cloth down and just dab at it with the end of the brush until it sticks, then make sure to apply enough resin over that to completely soak it. It will turn from white to a yellowish transparent when it is soaked. Continue to do this over the whole mold area. I let the first layer dry for about 8 hours, just cause i wanted to make sure it was done, and it was a bit humid here that day. Most of my coats i let dry overnight just because i had the time. If you want to go quicker, 2-3 in a dry environment will be ok. Putting them in the sun helps a lot too.

Here is my mold after coat 1 of fiberglass cloth. You can hardly see it.

It seems awkward at first, but you get the hang of it pretty quick. Here is after the third coat (1 cloth and 2 mat layers)

Get used to creating brush statues. After your resin either runs out, or starts to harden in the plastic mixing cup, leave the sacrificial brush in, and in a few hours, you can crack the whole thing out leaving your cup clean and ready to use again.

After the third coat has dried, it will be strong enough for you to remove it from the car. It may flex, but it won't break.

*Note* Because of the fuel door and piping, both sides will not be exactly the same. I worried about how I would get them the same prior to starting the project, but you just have to get them similar.

Life gets a lot easier when you can work on the molds outside of the car. This is after the 5th layer (1 cloth, 2 mat, 1 cloth, 1 mat)

I test fitted my form after layer 7. Everything looked good.

Continued Below (image restriction)


33,860 Posts
need to log in. i dont have facebook

816 Posts
Discussion Starter · #5 · (Edited)
Continued from Above....

Now, after whatever layer you deem is thick enough for you (I chose 7) then you can start to think about what shape you want. I figured mine out and then used a jigsaw to trim it up.

Both trimmed

Next you want to cut out your MDF Rings if you are making them

Again, I just used my jigsaw to cut these out. You could use a router, but really they don't have to be perfect. I test fitted mine in this pic.

Next comes the hardest part of the whole project, in my opinion. You have to suspend your MDF rings well enough that they will not move when you stretch your fleece over. I just made strips out of some left over wood I had, others have used wooden dowels. Basically, you figure out where you want your ring, then use hot glue to hold the supports in place. This takes a while.

After your ring is in place, take some fleece and start to hot glue it to the back of the form, stretching it over the ring. You will get rolls, but you can stretch them out.

After you have secured the fleece, trim the excess.

The next step is adding resin to the fleece. Fleece is great because it soaks up the resin really well. You want to make sure you make more mixed resin then before, because you will use a lot here. Make sure you let the Fleece completely soak up as much resin as possible.

If you don't, this will happen:

What happened was i ran out of resin and by the time i mixed more and came back, the top had already started to harden, but it wasn't soaked. I later had to resin the inside to fix this. Not fun.

I did two coats of just resin over the fleece. It gets quite hard

I cut the center, and then hot glued and later resin'd the triangle flaps around the mdf ring, giving it more support. I cut out my supports after the resin on that coat had dried.

Make sure to resin all the way over the edge and on the back. Those little imperfections help the box stay in place later.

I did one layer of just resin on the inside. Some people do more, and even mat or cloth inside. After my two layers of just solid resin over fleece on the outside, I did one layer of cloth and let that bake in the sun. It was more than strong enough.

After this, I did another test fit (mostly for fun to see how it looked)

Now, after you have fleeced, resin'd, and used mat or cloth on the outside, chances are your ring grew a little on the inside, so that your sub won't fit. I don't have an air sander, but I know someone who did. I used that to round out the inside of the ring and sand down all the rough edges from the boxes.

It's a good idea to test fit your subs, and get the screw holes figured out

If all has gone well, it's time to get your cover material. Most use carpet, some use paint. (The prep work for painting is enormous, and you will need bondo and lots of sanding, but you knew that) After looking around locally for carpet I wanted, I thought well, fleece is cheap, looks good, it's pretty durable, and stretches very well. I had already used it once, and I liked it. I went out and got some at walmart, in a gray color that doesn't necessarily match but is close to my interior.

So I proceeded to glue it on.

If you want to do carpet here, you should use a can of spray adhesive to attach it.

Side note, my MDF ring board made a perfect makeshift workbench, because when i needed to work with the box from the front, I could set it in the holes and it was easy to work with...

Make sure you can find your holes again after covering the enclosure

Also, its is perfectly OK to leave the back uncovered, in fact I recommend it. It fits better into the car, especially if you took time on your mold.

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816 Posts
Discussion Starter · #8 · (Edited)
Continued from Above:

Now it's time to start installing the hardware. If you are doing speaker terminals, you don't want to screw them into the fiberglass only, you will need to put some mdf behind them as well. This will allow you to tighten your screws to make an airtight box. You don't want to crack or break your box trying to tighten these against just Fiberglass. I measured and cut out my backing with a jigsaw. (used old mdf ring cutout)

Now, because of my Sub/Amp setup, I needed two terminals on one box, because I have a mono amp and my subs are Dual Voice Coil 2ohm. This requires me to run wire from the amp to sub 1, then out sub 1 to sub 2.

You will want to also seal your terminals with some silicone or at least hot glue to preserve the sealed box.

From here on, there's a lot of personal choice involved. My subs require .65 to 1.25 cu. ft. to operate to specification, and my enclosures are really close to 1 cu. ft. To get the best sound, I decided to line the boxes with dynamat to keep the sound tight and punchy. Because I had room to work with, space-wise, I also added poly fill, which will trick the subs into thinking they are in a bigger box. You get about .1 to .2 extra cu. ft. per 16oz of Poly fill. I did 16oz in each box.

After that, you're pretty much done! Re assemble everything and enjoy!

I will take more pictures of them installed when I get a chance.

Also, I do want to add that I added a bolt / washer on the inside so that I could secure them to the car and make sure they won't go anywhere. I weighed the Boxes after i was done, and they are only about 23lbs each, sub included which is at least 12 by itself.

I hope that this information is helpful, and if you have any questions feel free to ask here or PM Me. This is my first writeup, but I hope everyone likes it. :noes: :pray:

Thanks!!!! :thumbsup:

03 ABP Type-S
323 Posts
how hard is something like this for someone who has never used fiberglass?
It's not too hard, I just finished making one myself and had never done fiberglass before it took a few to get used to but you get the hang of it. Just take your time and be patient. My box took me 3 weeks, just need to carpet it now, waiting for that to come in mail because I had to order it :(

816 Posts
Discussion Starter · #13 · (Edited)
how hard is something like this for someone who has never used fiberglass?
I also had never worked with fiberglass prior to this. Definatley easy to learn, although it would take some time to master. A novice can do this project relatively easily.

they call me Marsh
14,483 Posts
I also had never worked with fiberglass prior to this. Definatley easy to learn, although it would take some time to master. A novice can do this project relatively easily.

I will have a full writeup in a few days.
lookin forward to it!

816 Posts
Discussion Starter · #17 · (Edited)
nice ill probably try this soon then whats the sound like compared to the subs being in a box?
The sound actually surprised me. I have a new amp on the way, but until that shows up (Thursday) I just hooked them up to my old amp (150W @ 4ohms per channel).
It was amazing. Before, I had them pointed toward the hatch rear, and it was good, but now not only does the sound just incredible and punchy, but I can really feel it.

When I hooked them up prior to installing the dynamat and poly fill, they sounded good, but I can definitely tell the difference adding those two things make. I highly recommend it!

Pics of them fully Installed soon!!!!

816 Posts
Discussion Starter · #18 ·
theres a DIY for this already but its only for one corner, but the process is the same
Very true, but I've done a few different things and It probably won't hurt the community to record it all.

443 Posts
nice one, i wanted to do something like this with my subs but never got around to it. and I couldn't pass up a $70 sub box that was originally $250 or something.

i wanted to make 2 custom ones and put em in the same place you did. :thumbsup:
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