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Fiberglass and MDF sub enclosure walkthrough

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  • Fiberglass and MDF sub enclosure walkthrough

    This thread will be a good source of information about how I personally constructed my custom Subwoofer Enclosure. This information can be used for ideas on how to build your own box, and has tips about working with MDF and Fiberglass. This is informational only and not meant to provide any sort of warranty or any other guarantee that you will not mess something up, therefore, follow these steps at your own risk. This is not a claim that this is the BEST set-up for every person and every vehicle. This sport (I call it a sport rather than a hobby due to the endurance and strength of wit required for avid enthusiasts.) has an infinitely variable number of set-ups that wll work for each and every driver/vehicle combination. Keeping that in mind, I've also provided information and tips for other set-ups. Enjoy.

    1. Planning:
    The first step is to consider what components you want to use, in my case, I'll be using two Infinity Reference 1241W 12" DVC subs, and my existing sony amp. Also consider the location for your subs, while keeping in mind that cargo space will usually be sacrificed for your set up. Some set-ups allow the subs to be placed behind the wheel wells, in the spare tire well, or just behind the seats. I'll be using the latter, since I don't usually carry around large items in the trunk, and I'd like to use the wells behind the wheels for storing the computer components and other storage space, so this works for me. Also, I will still want access to the spare tire, so I have constructed a new floor out of MDF that spans the entire length of the trunk. This is another thing to consider when designing the box.

    2. Design your enclosure:
    Whether you use old fashioned paper and pencil, or a computer design program, it's good to have an idea of what the finished project will look like. This helps during the fabrication process by giving a reference of location, measurements, etc. I will be using some MDF for any flat wall on my design, and making a sketch provides a reference for making cuts, and how much material I will need. Here is a diagram of the skeleton I used for my enclosure:

    Note how this is just for the MDF, the fiberglass will come later.

    3. Gather materials:
    I'll be using two sheets of 2' x 4' x 1/2" MDF. This provides a solid structure for any flat surfaces. Also, I'll need some fiberglass mat, resin and hardener, latex gloves, plastic mixing bowls, stirring sticks, cheap paint brushes, breather mask (not optional), rotozip or similar cutting tool, razor blade, jig saw with blade suitable for MDF, varying grit sandpaper (lots of sanding ahead), See post #2 for cost and suggestions for these materials, as well as other materials I used.

    4. Cut your frame out:
    I'll start by laying out and measuring the cuts I will make onto the MDF. Most people recommend 3/4" MDF, but personally, for my set-up, I'll be using 1/2" MDF; it's only a few bucks cheaper, but for me, it's about keeping some of the weight down. 1/2" MDF is 66% the mass of 3/4" and only slightly weaker. Keep in mind that different materials have a different resonance, and your enclosure may sound strange using the wrong materials. Use the rule 'measure twice, cut once.' I usually measure a few times from different sides to make sure the measurements are correct. Make sure that the blade width is considered when making these cuts.


    5. Construct the frame:
    My frame is simple, three panels, and the sub rings, which have supports not pictured in the diagram. More on this in post #3. So I need to measure the location of the center divider. This keeps the air seperated between the two sides.



    From the back of the back panel, I pre-drilled the holes where the screws will go, at a measured distance. This keeps the wood from splitting. For a flush look, countersink the screw heads. Personally, I like to use a screw for every 2.5" - 3" of wood, for the back part, the piece is 15" in length, so I'll be using 4 screws (see picture.)

    I started the measurement from the edge, 3" in, then the other three screws were placed evenly along the rest of the length. Then I did the same to the bottom panel, placing screws all along any joint between the two pieces. Wood glue now will help seal everything later. I also backed this up with silicone sealant, (look closely in the second and third pics in this step.) Keep in mind that you want to keep the screws at least the distance equal to the length of your screws from any edge. This keeps the screws from deflecting on each other, which can split the wood, among other things.

    6. Test fit the naked frame:
    Now is a good time to make sure that you measured correctly and test fit the frame in the car. Make sure there is plenty of clearance for hinge supports, and any wiring that is in the trunk. Adjust your plans as necessary. Some people will make a cardboard mock up of the box for test fitting. For me, since everything fits right, I will seal the edges of the frame to prevent any air from escaping the box. I used a simple clear silicone sealer.


    7. Strech fleece (or alternate material):
    I used a polyester based fleece (since the resin is polyester based) that I purchased at wal-mart in their remnant section, it won't matter what color or pattern it has, since there will be many layers of fiberglass mat on top of it. As long as it stretches, and has a polyester base, other fabrics may be used. Start to staple the fleece from the center and work your way out around your frame. Make sure that the fleece is taught and there aren't any wrinkles at all. For complex corners, you may cut a slit in the fleece to allow the curve or corner to overlap rather than wrinkle. This will save some time when all the layers of mat are applied.



    Now is a good time to check for the correct volume, I used packing peanuts for reference. Fill up a box with known dimensions and pour the peanuts in to the enclosure, if the peanuts come close, you can move on to the next step. Don't forget to account for the sub's volume too, it takes up air space as well. Here's a simple rule of thumb: For every 1" diameter use .1 Cu Ft of air space, example: 12" sub, usually requires 1.2 Cu Ft. of air space. Of course, consult the user guide or info sheet that came with your sub or that can be found on the manufacturers website. Also remember a cubic foot is 1,728 cubic inches. (12x12x12)

    8. Apply resin:
    Mix the appropriate amount of resin and hardener, the instructions are on both containers. For the Bondo brand stuff, it's about 14 drops per ounce. The disposable plastic containers by Glad and Ziplock are great for this, they are inexpensive, and since the resin doesn't bond with this plastic, it can be cracked loose for reuse later. I like to have a few of these when I'm doing this step, I'll be doing two layers at once, and the resin sets up fairly quick. I can use two containers, the second one to mix more resin while the first layer sets up. Make sure the fleece is well saturated, a common mistake that first timers make is not using enough resin, making the foundation a little weak. This layer will soak up the most resin, and therefore will use more. Use a brush to coat the entire surface of the fleece. Also, go past the edges of the sub rings, but it is not necessary to apply resin to the centers; you will just be cutting this out later, no need to waste the resin.

    9. Lay up initial fiberglass mat layer:
    After the fleece is completely saturated, you can begin to lay up a layer of mat immediately if you'd like. Rip the mat so that there are frayed edges, and apply in small squares, about 3" x 3" and in strips along curves and other hard to form shapes, about 2" x 4" long. (these sizes are just recommendations and approximates, please don't pull out a ruler for this step.) make sure the mat completely overlaps the fleece. This is your first layer that will provide strength and structure to the resin. Make sure the area is well ventilated and you are using your breather mask. Fiberglass fibers are really small, but very sharp, and can literally tear apart your lungs if you breathe any. (just like glass shards can tear apart your skin) You don't want to risk it, so buy a quality mask, if you can smell the resin through the mask, it's not good enough, this means that particles are passing through the mask and in turn into your lungs.

    10. Lay up additional layers of fiberglass mat:
    Once the foundation layers have set-up (not cured yet though) it is time to lay up more layers of resin and mat. Brush resin onto the existing layer, then place a piece of mat, and cover it with resin until it's saturated. Be careful to spot any bubbles at this and every layer. The preferred method is a dabbing technique, this squeezes the air out of the weave and pushes resin in it's place. If a lot of bubbles are forming in a particular place, smaller pieces of mat are recommended. Again, make sure to overlap the previous layer completely, and glass past the edges. Repeat this step a few times until the thickness is about 1/2" - 3/4". This is usually 4-8 layers depending on the mat that is used. When laying additional layers, you may not have set aside enough time for each layer, and will have to apply more after the layers have set and cured. This is not recommended; set aside an entire day for this. (Professionals can complete an enclosure in much less time, but if you were a pro, you wouldn't be using this guide to make your box.) As long as the resin hasn't cured, more layers can be added, and will be chemically bonded to the previous layer. If a layer cures, then it will need to be sanded to a rough texture for a mechanical bond, which has less strength. Did you remember to wear your breather again? If not, I'll see you in the hospital; it's not worth the risk.

    11. Allow plenty of time for the resin to cure:
    This usually takes 1-4 days for everything to cure correctly. A lot of people will tell you that it's not done until you can stand on the box and it supports your weight. Refer to the containers or the supplier for this time frame. The box should be completely dry to the touch, and not flexible at all.

    12. Sanding and prep work:
    Once the glass is completely hardened and cured, you can finally begin the prep work for finishing. Using a coarse grit sandpaper, start to sand the enclosure to a fairly smooth shape. For the first coat of filler, I prefer to cover the entire enclosure. After the layer sets up, sand it with a sanding sponge or sand paper on a sanding block (or if you have access to one, a powered sanding wheel is a great time-saving tool.) Blocks and sponges are recommended here since these are flat, and your hand is bumpy. Sanding this and future layers with your hand will create an uneven surface. Apply more filler to spots that need it, and sand some more. Repeat until you have a fairly smooth surface with no dips or unwanted bumps. Also, the subs will need a flat surface to mount to. I prefer to sand the sub ring all the way to the MDF, but if you use a double ring to inset the sub, this is less necessary. (Info on MDF rings, and support ribs below Post #3)

    13. Cover the enclosure:
    I will be using carpet, so the enclosure does not need to have an immaculate finish, just one that has no big dips or bumps. (The carpet will hide some small imperfections.) First I'd lay out the carpet, and apply spray adhesive to both the carpet and the box. (3M makes a good product in various strengths, I used super 77 for this one.) Let it set up for a few seconds and start to lay the carpet onto the enclosure. Curved shapes are harder to carpet, but most automotive carpets are a little flexible and all that is required is a little stretching to make it work. Sometimes you will have wrinkles in the carpet. The easy way is to cut a slit to the corner, allow it to overlap, and cut down the middle. (See post #4 for more info and pics for this step.)
    If you are planning to paint your enclosure, you will need to have a perfectly smooth surface. Repeat the bondo/sand steps above, until it's close to perfectly smooth. Wet sand the surface for a perfect finish and prime and paint it. Most body shops will do this step for you if you want a really great finish. I prefer carpet since that's what's in my trunk, I'd rather not have the enclosure pop out at you visually. (Some prefer this however to show off the system.)

    14. Wire the system and install:
    Hopefully in the design stage, you considered where and how you would like to wire everything. All you need to do is drill a hole big enough to run your wire, then seal the hole with more silicone sealer. You need this enclosure to be airtight since subs use air to make sound. Install the subs in the rings, make sure the seal here is airtight too. Some people have used weather stripping or caulk for this. For my box, the rings are flat and need little to no help providing a great seal. I'll be using a few different types of screw heads for security. You can get some different screws at your local hardware store. This makes it just a little harder to steal everything. The thief has to change bits, if he even has a drill and the bit needed for the screw, and this takes time, which is the thief's greatest danger. Install the box in your car and fire up your system. I have secured the box straight into the trunk floor, which was redone with MDF for more strength. Just be careful to not drill through and hit the fuel tank or lines. (Velcro on the bottom surface works well on carpet, use the hook side.)

    15. Enjoy the great sound and sense of accomplishment it brings having made a custom sub enclosure.

    Please post any questions to this process and if the mods like this enough, maybe it can be a sticky since the other fiberglass post is a little disorganized. If you'd like to post "dude that's nice" comments, you can visit my worklog and Project threads for this.
    2007 Chrysler PT Cruiser TE
    Car PC Progress:
    Planning.......[---------X-] 95%
    Parts...........[---------X-] 90%
    Fabrication...[---------X-] 90%
    RR Skin........[---------X-] 95%
    View my
    Worklog
    Road Runner Skins
    Website
    Favorite thread EVER!

  • #2
    reserved for materials information
    2007 Chrysler PT Cruiser TE
    Car PC Progress:
    Planning.......[---------X-] 95%
    Parts...........[---------X-] 90%
    Fabrication...[---------X-] 90%
    RR Skin........[---------X-] 95%
    View my
    Worklog
    Road Runner Skins
    Website
    Favorite thread EVER!

    Comment


    • #3
      reserved for MDF frame and Ribs information
      2007 Chrysler PT Cruiser TE
      Car PC Progress:
      Planning.......[---------X-] 95%
      Parts...........[---------X-] 90%
      Fabrication...[---------X-] 90%
      RR Skin........[---------X-] 95%
      View my
      Worklog
      Road Runner Skins
      Website
      Favorite thread EVER!

      Comment


      • #4
        Reserved for carpetting information
        2007 Chrysler PT Cruiser TE
        Car PC Progress:
        Planning.......[---------X-] 95%
        Parts...........[---------X-] 90%
        Fabrication...[---------X-] 90%
        RR Skin........[---------X-] 95%
        View my
        Worklog
        Road Runner Skins
        Website
        Favorite thread EVER!

        Comment


        • #5
          Pictures will be posted as work is completed. I am building this Box just for this thread. I will start it saturday morning, check back sometime after for pictures.
          2007 Chrysler PT Cruiser TE
          Car PC Progress:
          Planning.......[---------X-] 95%
          Parts...........[---------X-] 90%
          Fabrication...[---------X-] 90%
          RR Skin........[---------X-] 95%
          View my
          Worklog
          Road Runner Skins
          Website
          Favorite thread EVER!

          Comment


          • #6
            bump to say I posted some pics and started the box, Stretched the fleece, then had to go, so that's where i'm leaving it for now. More pics soon.
            Oh, and by the way, the bump in between the subs is planned, I wanted a little something to add a little interest in the shape.
            2007 Chrysler PT Cruiser TE
            Car PC Progress:
            Planning.......[---------X-] 95%
            Parts...........[---------X-] 90%
            Fabrication...[---------X-] 90%
            RR Skin........[---------X-] 95%
            View my
            Worklog
            Road Runner Skins
            Website
            Favorite thread EVER!

            Comment


            • #7
              looking good

              2006 Mazda 3
              Behringer DCX-2496
              JL300/4 Focal 6W4311B Focal TN52
              JL500/1 JL10w6v2

              Comment


              • #8
                added pics, will do more tomorrow
                2007 Chrysler PT Cruiser TE
                Car PC Progress:
                Planning.......[---------X-] 95%
                Parts...........[---------X-] 90%
                Fabrication...[---------X-] 90%
                RR Skin........[---------X-] 95%
                View my
                Worklog
                Road Runner Skins
                Website
                Favorite thread EVER!

                Comment


                • #9
                  Hello just joined. Like the box. Funny you live in lakewood so do i. lol

                  Comment


                  • #10
                    That's cool, nice to have another Lakehooder around here. What are your plans with your CarPC project? What else have you done with your car?

                    This project was scrapped due to bad planning. I had a perfectly good square box anyways, and this was just for fun to see if I could do it. I've got a different car now anyway, and it's going to get a custom MDF box.

                    Welcome to the forums, sanegillespie1.
                    2007 Chrysler PT Cruiser TE
                    Car PC Progress:
                    Planning.......[---------X-] 95%
                    Parts...........[---------X-] 90%
                    Fabrication...[---------X-] 90%
                    RR Skin........[---------X-] 95%
                    View my
                    Worklog
                    Road Runner Skins
                    Website
                    Favorite thread EVER!

                    Comment


                    • #11
                      Originally posted by monkeyracer View Post
                      . . . This project was scrapped due to bad planning.
                      What was the bad planning we need to look out for if we follow this path?
                      .
                      If just enough is really good, then too much ought to be perfect.

                      2006 Scion xB with in-dash Atom & Lilliput 889GL -- Worklog at http://www.mp3car.com/vbulletin/work...res-links.html
                      .

                      Comment


                      • #12
                        notice in this picture:



                        There is a bump in between the two subs from a bad cut in the center divider. That and where there was a seam in the fleece, it didn't stick together the way it should have. Lastly, since it was "just for fun" I didn't budget what I should have to get this done, and ran out of resin way earlier than I thought.

                        So if I were to do it again, I would have redesigned the center divider, and bought more resin, and mat.
                        2007 Chrysler PT Cruiser TE
                        Car PC Progress:
                        Planning.......[---------X-] 95%
                        Parts...........[---------X-] 90%
                        Fabrication...[---------X-] 90%
                        RR Skin........[---------X-] 95%
                        View my
                        Worklog
                        Road Runner Skins
                        Website
                        Favorite thread EVER!

                        Comment


                        • #13
                          Well thank you man! I dont realy know yet i just found this site and decided to join. I think i am going to invest into equipment to start making custom boxes.

                          Comment


                          • #14
                            Too bad . . . you had a nice plan and a nice setup on the worklog. It would have been fun to watch it grow. I'll watch for your new box.
                            .
                            If just enough is really good, then too much ought to be perfect.

                            2006 Scion xB with in-dash Atom & Lilliput 889GL -- Worklog at http://www.mp3car.com/vbulletin/work...res-links.html
                            .

                            Comment


                            • #15
                              Good work up, but I only have one thing to criticize, the use of fleece...

                              I am not flaming you or anything, but wanted to state this for newbies to fiberglassing.

                              expandable polyester like swimsuit material or spandex is much better than fleece for fiberglass work. It is so much easier to make complex curves with, and you can stretch it uber-tight holding it down with CA Glue or staples.

                              When applying resin on spandex type material, you do not have to use as much, thus reducing some of the costs involved in enclosure fabrication. Fleece soaks up way too much resin and gives people a false sense of security because of the thickness and the it is strong as a rock attitude after the resin dries. I have seen too many people crack boxes because they used fleece, then not enough fiberglass cloth for strength.

                              Yes, we all know that the number of layers of fiberglass cloth laid down gives you the strength to your structure. Fleece just gives too many people a false sence of security. A sub enclosure has to be balls-to-the-wall solid, with enough layers of fiberglass.

                              I just wanted to make this point so that newbies to fiberglass don't fall under false sense of security. Once again, not to be as a flame, just informational.

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