Fiberglass Subwoofer Box

I am no longer selling this subwoofer box. I broke the mold and can no longer produce them

Putting bass in a Miata has always been a problem. There have been several solutions over the years, some better than others. I think mine is one of the best. I will admit to one fault right away though, there is a loss of seat travel; this is not a problem for me though because I wasn’t using the travel anyway. To get an idea of how much seat travel is lost take a look at these two pictures which show the box in relation to the seat belt towers. Picture 1, Picture 2.

This project took me about four months to complete and more money then I care to admit to, but in the end it was all worth it. The box is primarily constructed out of fiberglass, the only wood part is the front face that holds the speakers themselves. I have had a ton of emails asking me how I did it so here it goes.

First things first, if you don’t know how to work with fiberglass and want to learn, I suggest buying the book Fiberglass & Composite Materials. This book is very well written, not overly technical, and packed with useful information. Another resource that I found to be of great help for fiberglass and car stereo stuff in general was the Carsound forum. Doing a search in the “Matt Borgardt on Fabrication” section on fiberglass will give you a couple days’ worth of reading. I found that most of the questions I had while constructing the box could be found by searching the archives; and if I didn’t find the answer from a search, I would usually get a good answer by posting a question of my own.

All right, after you know how to use fiberglass you can get started.

What I did first was to remove everything behind the seats (carpet, rear deck, etc). Then I laid tin foil and clear packing tape down all over the places that I was going to put fiberglass down (fiberglass doesn’t stick to the tape or foil). I then laid the fiberglass directly in the car and let it dry. This gave me the contour around the gas tank and the rear shelf area; this piece serves as the bottom part of my enclosure. Next I took some MDF and cut out the shape that would be the front of my box. I attached the MDF to the bottom fiberglass part using screws. Now I had to make the shape for the top of the box. I went and bought a bunch of styrofoam (which is surprisingly expensive) and attached it to the MDF spanning across the fiberglass section.

I then used a carving knife and sandpaper and shaped the Styrofoam to the desired shape. Next I covered the Styrofoam with tin foil and packing tape (fiberglass resin will eat Styrofoam real quick) and laid up fiberglass over the foam. After the fiberglass was dry I spent a long time applying bondo and sanding down the fiberglass to make it perfectly smooth. After the sanding was done, I pretty much had a complete box. I took it one step further though.

Now I had a completely smooth finished piece which I used as a plug to make a mold. I am not going to discuss the mold making process; but if you really want to know how, feel free to contact me and I can give you some pointers. Now that I have a mold made, I can make copies of the box whenever I want.

*UPDATE: I AM NO LONGER SELLING THESE BOXES, I BROKE THE MOLD AND CAN NO LONGER PRODUCE THEM* I do want to sell copies of the box; so, if you are interested, please send me an email. I am selling complete boxes covered in your choice of colored vinyl, with all the mounting hardware, and the Miata script (optional) for $400, this price does not include the speakers.

If you think this is high, realize that there is about a hundred dollars worth of materials in each box and it takes me about five days to make one. In comparison the JL Audio stealth box runs around $700, but it does come with speakers.

Just a few more things that I forgot to mention earlier, the box sounds fantastic I do not have “hear it ten blocks away” kind of bass, it is more tight and what I call musical, it does hit pretty low and hard though. The box has an approximate volume of .8 cubic feet and I am running two JL audio 8W3 Subwoofers in it. The box is filled with polyfill as well.

Here are a few pictures of a tan box that I made for someone.
Tan box 1
Tan box 2
Tan box 3
Tan box 4

Comments & Questions

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13 Questions/Comments/Trackbacks so far

  1. Posted by: sean
    January 24, 2010 9:53 pm

    i have a 2001 mazda miata i like the box but were does the GLASS window for the top go and how well does it fit with the box in the car. please let me know sub boxs r hard to find. email me back at thanks

  2. Posted by: Moe
    January 25, 2010 12:34 pm

    Look at the pictures, my car has the glass window.

    FYI, I am no longer selling these boxes.

  3. Posted by: Kevin Schmidt
    February 2, 2010 5:22 pm

    You should produce these again… I would purchase one…

  4. Posted by: Moe
    February 2, 2010 5:58 pm

    They were a hell of a lot of work to make, even with a mold. Someday I would like to build version 2.0 but I have no idea when or if that will ever happen.

  5. Posted by: pallet wrapping
    November 11, 2010 8:39 am

    The tan box looks really nice in those images. I have a small car so I’m a bit worried about getting a bass in it, I don’t want to damage either the box or the car so it’s always difficult to know how to go about it.

  6. Posted by: joe
    April 22, 2011 10:12 pm

    i would like to get one of those boxes do you ship to apo

  7. Posted by: Moe
    April 23, 2011 9:28 am

    Joe, unfortunately I no longer sell these boxes. As stated in bold at the top of the page and in the body of the text” I am no longer selling this subwoofer box. I broke the mold and can no longer produce them”

  8. Posted by: john s
    September 23, 2011 5:54 pm

    dude that box is what im looking for i would so buy one off you if u still sell them 😀 thats just wat i want it looks awesome it goes with a roll cage and every thing 😀

  9. Posted by: Ava
    March 6, 2012 4:48 pm

    Dear Sir:
    This is Ava from RELL CONSTRUCTION MATERIAL COMPANY , a manufacturer specializing in producing construction materials in China. We have cooperated with customers from Europe, South Africa, Asia, North America, etc since the establishment of 1998.
    Our main products include fiberglass I-beam, fiberglass construction profiles, fiberglass gratings, FRP molded gratings, FRP sheets, FRP pultruded gratings, stair tread, , walkways, handrails, anti-slip nosing, man hole covers, ditch covers, stair way, FRP anti-corrosion products, etc. Please have a look at our website:
    We can provide you with quite satisfactory products and service with the best quality at most competitive price. We are looking forward to establishing win-win business relations with you.
    Best Wishes

  10. Posted by: john
    November 15, 2012 2:37 pm

    HElloo good sir. I like the sub box you have made its very nice and clean and saw that your mold had broke, but i was woundering if you could get me the info on it and some of the messurments that you had taken to help me build one

  11. Posted by: Steven Terzich
    January 24, 2017 10:23 am

    Hello, I was wondering if you possibly still had some black boxes? I am very interested in possibly purchasing one if so. Please let me know would be sooo nice. Also non wrap ones I’m looking for.

  12. Posted by: Willie Trent
    February 10, 2022 4:10 pm

    If I could get the measurements considering you are not making these any longer? I have been attempting to do something similar with my Miata. Thank you, WT

  13. Posted by: Moe
    February 17, 2022 8:38 am

    Willie, unfortunately it’s such an organic shape that providing measurements would essentially be impossible. Sorry.