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Fiberglass Sub-box Walkthrough


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Ok, there have been a few people that have made fiberglass subwoofer enclosures for the small spaces in the trunk behind the fender and in front of the tail-light access. I looked at their work and it was very nice, so I figured, how hard would this be? It couldnt be horribly hard right? This is true, its easier than you think.

So, how do you turn Picture 1, into something less bulky, space consuming? Very simple.

 

Materials needed/recommended:

 

Most of this is available at Wal-Mart in both the paint and automotive sections

 

*(4oz fiberglass mat woven cloth 3-4 packages of 8sq ft per enclosure(each side of your car)

*2 cans of bondo fiberglass resin (includes hardener in the top, but it wont be enough)

*2 extra tubes of bondo fiberglass hardener

*Cheap paintbrushes for applying the resin

*Containers for mixing the resin (I just bought some of the gladware 4oz containers in the cooking section of Wal-Mart. It was the easiest way to measure the resin and hardener, and it was about the right size to apply it before it started to harden.

*Popsicle sticks for mixing the resin and to help with the mold

*Latex powder-free gloves -- lots... you will need about 7 pairs the way I did it.

*1 container Acetone - clean brushes, containers, hands, mistakes, ect

*Liquid Nail/caulk -- sealing the box, and I used it to hold on the carpet.

*Industrial Strength Velcro -- self adhesive kind

*Speaker wire -- use recommended size or better for your sub

*1 sheet of 3x6 MDF (I used 1/2inch)

*1 Subwoofer enclosure carpet -- I bought mine at a local car audio store, it was almost identical to the stock interior in the trunk.

*1 roll of aluminum foil

*1 roll of 1/2 - 1" masking tape (per side)

*newspaper, cardboard, packaging paper, ect... whatever you feel safest using for protecting your interior and paint.

*Sanding paper, almost any grit will work, just enough to get a rougher surface to apply the fiberglass to itself.

 

 

First: You masking tape off the area inside the trunk to prepare your mold. Masking tape an area much larger than you plan to actually use, this way you wont leak any fiberglass resin on the trunk interior. (pic2)

 

Second: Take newspaper, packing paper, cardboard, or anything else that you like and cover the rest of the trunk with it. Be sure to tape it securely into place so that it does not slide around. Also cover the outside of your car so that you do not leak onto the paint or window. Proper preperation will be time consuming (took me about 2-3 hours) but it is worth it. You dont want your car to be damaged. (pic3)

 

Third: Form aluminum foil to the outline of your masking taped surface. This provides added protection against leaking resin on your interior. Be sure to apply it to a larger area than what you want your mold to be. (pic4)

 

Fourth:Mix your resin in accordance with the directions on the can. Cut small squares of fiberglass cloth (4x4 inch, whatever you feel comfortable using) and lay them in place and apply the resin over the cloth making sure to give it a full soaking. Your first layer of fiberglass will most likely use more resin than the other layers. Apply the layers of cloth overlapping eachother some to provide a secure bond. Cover the entire area that you want the mold to form to, making sure to make the mold a little larger than what your final mold will be. It is easier to cut the mold down than to apply more layers to make it bigger. It should end up looking similar to (pic5).

 

Fifth: Wait for the mold to completely dry. Then carefully remove it from the car. If you used the bondo resin, it says complete dry in 2 hours. I waited about 4 before I pulled it out. I was going to let it set overnight, but circumstances would not allow that. :| Once the mold is removed you can take off all the masking tape and everything else inside the trunk.

 

Sixth: (pic6) is a picture of the mold in a test fitting. This is only the 1 layer of fiberglass. By the end I had 3 complete layers.

 

Seventh: Before applying another layer, sand the inside of the box/enclosure (do not apply more fiberglass to the outside of the box because it is a perfect mold of your trunk, if you do apply more to the outside it will become too large to fit and you will have wasted some time and $). You do not have to sand it really hard, just enough so that the next layer of fiberglass will bond to it.

 

Eighth: Mix more resin, apply fiberglass squares, cover the whole inside of the box again. Wait for complete dry. Then repeat steps 7 and 8 until you have the thickness you desire (I did 3 layers in total to include the first mold)

 

Nineth: Test the mold in the car again when completely dry, just to make sure it still fits. Then draw an outline of where you want the enclosure to come out to, distances ect.

 

Tenth: I used a jigsaw to cut the outline of the enclosure. (do not cut it inside the car... not that you would, but just in case I am saying this... you never know what people are apt to do.)

 

Eleventh: Lay the cut enclosure on the MDF and draw an outline of the enclosure. Cut the outline out with the jigsaw. You will most likely cut the MDF a few times before you get the proper fit. Cut it just enough so that it fits flush with the fiberglass enclosure. Once you have cut the MDF to the proper size, take your subwoofer cutout (normally comes with the sub when you buy it so that you can make your own box if you like.) and draw the outline on the MDF and cut out the proper size for your enclosure. (pic 7 + 8)

 

Twelve: Sand some of the outside of your fiberglass enclosure and some of the front of the MDF for a secure hold to the next layer of fiberglass you are going to apply.

 

Thirteen: I used car stands that I dont use any more to hold the fiberglass mount so that it wouldnt move around when I was applying the fiberglass to the MDF. Just make sure that the fiberglass will not have to be moved until its dry because you dont want the MDF and fiberglass mold to move around and come un-done.

 

Fourteen: Mix the resin and apply strips just enough to cover the MDF and just a little bit on the fiberglass. You dont want it to cover too much of the outside of your mold or else it will not fit back in your trunk. (repeat steps 12-14, I applied 2 layers to the MDF/enclosure just for added airtightness.)

(pic 9 + 10)

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Fifteen: Once the project has completely dried. Test fit your enclosure again. (pic1)

 

Sixteen: Remove the plastic cap in the trunk area, (cap is removed in pic2, and wire is stuck in there.) this is where your speaker wire will go. Match the hole, with the respective area on the back of your fiberglass box. It doesnt have to be exact, just a good estimate. Then drill the hole in the back of your box, just big enough for the speaker wire to fit.

 

Seventeen: Put the speaker wire through the hole. Give yourself enough extra wire to work with and to connect to the back of your sub. Then use the liquid nail/caulk to seal the hole completely, front and back. (pic 3 + 4) Also at this time (i forgot to do this, but it still worked out in the end.), use a drill to drill the holes for the subwoofer screws. You can do it later, but it will be more difficult to do with the carpet on.

 

Eighteen: Once that is dry lay your box on the carpet. Cut out a piece of carpet large enough to cover the front and to overlap to the back some for a secure and non-showing hold. Use the liquid nail (or epoxy glue might work) to glue the back of the carpet to the sides of the box. Make sure that the carpet goes back far enough so that it will look smooth when you have installed it. It will be a bit of work getting the liquid nail to stick, getting the mold fit without wrinkles, forming it to the shape of the box, ect.

 

Nineteen: Once the glue is dry, then you can cut from the middle of the speaker hole, to the outsides of the speaker hole. Somewhat like you cut a pie. I would suggest not to cut the carpet in a round shape to match the hole. I took the carpet (trinagle shaped pieces) and pulled it tightly into the hole and glued it inside the box. This way it took out any wrinkles that might have been left on the front of the enclosure. (I might try and take a picture of this step with my next box.)

 

Twenty: Once the glue is dry, place your subwoofer (also suggested is foam for helping seal your sub) in the correct hole and screw it in.

 

Twenty-one: Test fit your sub to make sure it still fits. Then remove it and apply the velcro to locations of your choice. I put 4 strips on, one on the top, and 3 on the sides, I didnt worry about the bottom because it was already secure without it when I test fited it, this was just for added security and hard cornering.

 

Twenty-two: run the wire through the hole in your car trunk and pull it through to your spare tire area. (from here you can mount the amps down here, or run it to an amp mounted elsewhere, or anywhere else that you like.)

 

Twenty-three: Push your subwoofer enclosure into place and make sure it holds.

 

From here, just enjoy. :)

 

I didnt notice any real sound issues from my MDF box. It sounded the same to me. I also cut my enclosure to allow the spare tire lid to open with the enclosure in. It barely hits the outer ring on the sub.

Hopefully this is helpful to anyone that might want to do this. If you have any questions dont hesitate to post or PM me. Also, I cant take the credit for this idea, there are a few others on here that did this before me. I just took from what they did and did some things my way and then wrote a walkthrough for it. So, credit goes out to those before me. Thanks for the ideas, they are great, and it has worked out nicely so far.

 

Enjoy. Mark

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Now for fun, calculate your internal volume and find out how close you are to the subs required specs....

As im new to that, how do you calculate the internal volume? I mean, I know all the mathematical fomulae to calculate volume taking depth and width and such, but thats a lot of different angles and whatnot. Is there an easier way to do it or anything else?

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Nice job!!

 

just a note for others who may want to build their own - 3/4" MDF is the 'norm' for subwoofer baffles. This is especially necessary with large drivers or high power - above 200 watts or so.

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fill it with water, measure the amount of water that comes out.

 

NO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

Sand is better as it won't soak into the MDF. MDF, when exposed to water, soaks it up like a sponge and loses it's density.

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Nice idea for the packing peanuts. I will have to do that sometime when I get the chance, or maybe when I make the other side(wont be for another week or so.). As for the MDF, I thought that 3/4" was the standard, but I couldnt find anyone who carried it, so I just went with the 1/2". But thats good information to know. Especially since I want to put in the JL Audio 10w3 or the 10w6... not sure yet... I think I will just go for the 3's though.
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I've been told that putting two subs in your trunk facing each other like that produces a canceling out effect that severly impacts the sound quality, have you noticed a difference in the sound of your subs with this conversion?

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I actually havent made the second enclosure yet. I havent had the time lately. I am hoping to get it done before I leave on my Christmas vacation.

If the sound turns out horribly, I might be selling the second enclosure then. As far as knowing whether it will sound horrible or not, I dont know. I dont know a whole lot about car audio in the sense of what is the best combination of x and y, and if x and y face in z direction the sound will be better or worse, I just know that one sub sounds better than the other one, these speakers sound better than those, connecting the amp, ect.

I will definately be updating the walkthrough when I go through it again. I think I left out a few things. Thanks for the thoughts though, I will let you know what happens.

Worst case scenario, I have to put one of the enclosures up for sale :) Maybe the sub as well. Then serious worst case... I would just have to get a JL 10w3... :p

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here is the one i did for my wagon..

http://images.snapfish.com/3456%3A73923232%7Ffp64%3Dot%3E2356%3D%3B7%3B%3D%3C%3B%3A%3DXROQDF%3E2324239%3C26356ot1lsi

 

http://images.snapfish.com/3456%3A73923232%7Ffp335%3Enu%3D3265%3E%3A8%3A%3E%3B%3C9%3EWSNRCG%3D323332%3A%3B35449nu0mrj

 

http://images.snapfish.com/3456%3A73923232%7Ffp336%3Enu%3D3265%3E%3A8%3A%3E%3B%3C9%3EWSNRCG%3D323332%3A%3B3544%3Anu0mrj

 

http://images.snapfish.com/3456%3A73923232%7Ffp335%3Enu%3D3265%3E%3A8%3A%3E%3B%3C9%3EWSNRCG%3D323332%3A%3B35454nu0mrj

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Nice install daswrx.

Infinity subs right? Did you also put new component speakers in as well? And where did you mount the amps? The first picture is a little dark, so I cant quite tell if they were mounted on the back of the seats or what.

Also, are the subs facing eachother, or are they slightly angled? Reason I ask, refer to post #16 and #18... Do you notice any degredation in sound quality because of their positioning?

Thanks

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there faceing eachother, no degredations at all with a ppi 1200watt amp. hehe.. the amp are in the spare tire. so no spare for me, i've got AAA and a cell phone. here is a pic of the amp for my mids.

 

http://images.snapfish.com/3456%3B6%3A%3B23232%7Ffp47%3Dot%3E2356%3D%3B7%3B%3D%3C%3B%3A%3DXROQDF%3E2324239%3C26362ot1lsi

audison vrx

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If the subs are perfectly aligned, then at any frequency where the waves converge, there would be a cancellation effect (in theory). However, since most subs operate in the lower registers (200Hz or less), the sound waves are over 12 feet in length. Also the chances of you custom fabricating two mirror image enclosures that perfectly align the drivers is almost nil.

 

In over 18 yrs of mobile electronics system design and IASCA judging I have never observed or measured cancelation from opposing sub drivers. In an anechoic chamber with scientific measurement equipment, it might be present. I just don't believe the human ear can perceive every defect that may be present in that frequency range.

 

just my $.02

Vir Est Fatum Ut Perficio Concepta Suus Progenies. - Man is destined to fulfill the capacity of his lineage (i.e. Darwinism):rolleyes:

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  • 3 weeks later...

I had built a similar setup in Phil Petracca's G35. 2 subs, one in each corner of the trunk. The Car did 138 db in it's first competition. I measured the phase response for each driver and it was very different. Running one of the subs out of phase gave us a peak SPL of 143. Quite a big difference considering no other changes were made.

 

Bill

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