How to Build a Fiberglass Sub Box

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Introduction: How to Build a Fiberglass Sub Box

In this Instructable i will show you how to build your very own custom subwoofer box!

Step 1: Making Room

Depending on your install you might have to remove some stuff from your trunk or cabin (spare tire,seats etc...)

In my case i have a single cab truck so my options are limited. I decided to take the bench seat out and install some bucket seats.

So i used the old bench seat mount and welded new bars across them, the new seats will mount to these and so will the fiberglass box.

Step 2: Picking a Box Shape

For this step we are going to cut a rough shape following the lines of the seats, Using cardboard for a template trace your new design onto the MDF

Now we can cut a front, back and bottom.

Looking good so far...

Step 3: Cut to Perfection

Now we can trace the outline of the seat onto the box.

I wanted it to look flush with the seats,also i didn't want to be hitting my elbows while driving so i cut as close as possible to the seats.

Then we use a router and rabbet cut all the way around the top edge off the box. This is necessary so when wrapped with fleece you will have some where to staple and will result in a lot less body filler.

Step 4: Cutting Rings

We need something mount speakers too!

So i made a simple circle jig out of plexiglass and attached it to the router.

Now we can cut four rings for the subwoofers.

Make sure to cut the outside of the ring first but don't cut all the way around the ring, leave 1 inch tabs on both sides of the circle (these will be cut with a jig saw after you cut the inside ring out)

Step 5: Flush Mounting the Rings

Next i bought some hardboard (hard bendable cardboard) from a upholstery shop.

For your speakers to mount flush you need to put your speakers face down and put the ring on top of the mounting holes.

Then cut strips of the hardboard to the height of the speaker edge and the ring, While your rings are still around the speakers staple the strips to the ring making sure not to staple into your speakers!

Now we mix up some resin and cut some fiberglass cloth into strips. First apply resin to the hardboard and then lay the strips of fiberglass and finish coating the cloth. I decided to resin the rings also but this is not necessary.

Step 6: Making Mounts

We need to mount the rings and depending on how your box is shaped this step will be slightly different.

For my install i cut small strips and cut an angle on the the end so i could adjust the angle of each subwoofer to my liking.

The mounts don't have to be really strong the fiberglass will be the strength

Step 7: Wrapping in Fleece and Applying Resin

This is where that rabbet cut will come in handy, start wrapping the box leaving 8 to 10 inches between each staple keeping the fleece moderately tight.

Now we can pull the fleece even tighter making the fleece curve around the rings stapling while pulling it tight you are going to staple all the way around the box with no space between them.

Next mix up a good amount of resin and soak the fleece with a thick coat, you want the resin to soak all the way through so don't be afraid when applying the resin!

Let the resin cure and apply a second coat before the next step...

Step 8: Fiberglass the Inside

Unfortunately I'm missing some pictures of this step but its pretty strait forward.

This is where it gets messy i recommend getting some latex gloves and a mask!

Cut up squares of the fiberglass cloth and and mix up some resin, coat the inside of the box with resin in sections and dab the squares of the cloth onto the fleece.

If you want a really solid box with a deep sound coat the fiberglass with two coats of kitty hair, seen in the above picture.

"Kitty hair" is short strand fiberglass mixed with body filler is sold at Home Depot or your local auto body repair shop

Step 9: Sanding, Body Filler and Primer

Here comes the fun part...Sanding!

Sand the area where we applied the resin with 100 grit to knock down the bumps and when smooth as possible apply a thin coat of body filler to the entire area

Go back with 100 grit and take out the rough edges the body filler will leave behind and work your way up 400 grit.

Now spray the whole box with filler primer and sand with 600 grit until smooth.

Step 10: Adding Ports

After putting the box in the truck i decided i wanted to port it...

So i bought some ABS pipe and a hole saw set.

Since the box is already built we can measure the air space pretty easily by either measuring with a tape measure and doing some math or the easy way and fill the box with packing peanuts and take that amount and fill up a square cardboard box, this will give you an accurate and easy way to calculate the air space.

Use an online port calculator to determine the length of the port needed for your enclosure

I cut the ABS to length using a band saw and then drilled out a whole in the box with a hole saw the size of the inside diameter of the ABS, then i cut a ring to accommodate the outside diameter of the ABS pipe and it will butt up to the hole cut into the box (see picture above)

Step 11: Paint or Wrap

Last step!

You can paint it your favorite color or maybe wrap it in vinyl, carpet or both like pictured above...

Thanks for checking out my Instructable!

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    47 Discussions

    This is really nice. Thanks for documenting and sharing the build so thoroughly. This is rad. Really impressive.

    This is probably the best looking box I have seen here on Instructables. Really nice job and looking forward to making my own some time soon.

    1 reply

    nice job!cant wait to start on mine!

    well done. good sub choice too

    That's some nice-looking glass work (although I'm glad that you and all those subs don't live anywhere near me). What did you use for the fleece and where did you get it?

    1 reply

    Thanks man and yeah i might be a little too loud but all in good fun!

    The fleece i buy at walmart or target, its like 4 dollars for a blanket thats usually big enough for any of my projects

    i just remembered that i need a new amp for the sub any idea where i can ge tone for cheap and if so what brand should i get?(cheaplike 20 -30 dollars)(it also needs to fit a pir of midranges and a tweeter)

    Nice instructable, but you never even mentioned calculating the proper space for your driver(s). This is a big part of making a box that actually sound good.

    1 reply

    i was planning to put a 10 inch sub on my drift trike now i can make a nice clean case for it thanks

    i was planning to put a 10 inch sub on my drift trike now i can make a nice clean case for it thanks

    i was planning to put a 10 inch sub on my drift trike now i can make a nice clean case for it thanks

    Nice and with my favorite subs too

    Excellent! I'll have to try this.

    Nice workmanship. Too bad what you built is completely obnoxious
    and absolutely inconsiderate of others. The base wave things like that put out will
    not fit inside of the vehicle. So as you increase the power trying to get the
    base you want all it is doing is disturbing others. The be nice policy keeps me from saying what should be done to obnoxious people that shake the windows from a block away with their subs.

    Here's a tip. Once you've stretched the fabric out and stapled it, use some CA glue (superglue on steroids available at hobby shops) to glue the fabric to the top of the rings. Dab the glue on the fabric where it meets the ring and rub it in so it soaks through the fleece and into your hardboard ring. I usually wrap my finger with masking tape and do this. Then spray it with the activator. Do small sections at a time like this. This does a couple things for you: It strengthens the bond between the fleece and the rings, it also allows you to resin just up to the edge of the ring and not over it which make cutting out the center a lot easier. You can just run a fresh razor blade around the inside of the hole to remove the material instead of having to cut out resin soaked fleece. Great job!!!

    1 reply

    I would also like to add this method could be used in lieu of staples in areas where you either cannot staple or exposed edges that need a smooth transition from fiberglass to substrate.

    Don't use fleece. It only wastes resin and adds no structure. Use spandex or t-shirts and build up with more than 2 layers of glass. Fiberglass gets its strength from the glass mat not the base layer used to lay the glass on.