OK guys, Here's a quick primer on building a fiberglass sub enclosure. Fiberglass offers a few benefits to typical wood. 1. Fiberglass is much lighter than MDF or even low void plywood. 2. Fiberglass is extremely strong. This makes it possible to make the enclosure thinner than a wooden enclosure further cutting the weight down. 3. Fiberglass can be made into any shape. You are limited only by imagination. Also, because of it's ability to conform to anything you can take advantage of every square inch of space that you have.
The enclosure you are looking at was built to take up the back seat of my Swift and is just over 6 cubic feet internal volume ported to 25Hz. The beginning part of the buildup is identical to what you would do for a spare tire well enclosure and there have been a few people wondering about this. If you guys have any other q's just let me know and I'll answer them to the best of my knowledge. Here goes...
SUPPLIES NEEDED:
Polyester resin
MEKP catalyst
Chop mat
Dust mask or respirator
Bucket for mixing
Patience
Measuring cup for MEKP
Absolutely the cheapest brushes you can find
Heavy duty foil (cheapest)
Duct tape (cheapest)
Stir sticks
Bondo w hardener
Patience
Box to hold mat
Dowel
Glue gun
Saw to cut rings
Staple gun
Fleece
Sandpaper
Latex/vinyl gloves
Oh yeah...did I mention patience?
PIC 1:
In this pic you can see what I did to protect the body from gettig messed up with resin.
There is a number of ways that you can do this (wax, vaseline, release agent, ect)
but I find this way much faster and less messy. Basicaly
I've covered the entire area that I will be working in with a couple of
layers of heavy duty foil and then covered all that with a layer of duct
tape. You will want this area to extend beyond your work area to make sure
that you dont get resin on it. IF YOU GET RESIN SOMEWHERE AND IT CURES IT
WILL NOT COME OFF!!! Make sure you protect the car.
PIC 2:
Make your frame. I use 3/4" MDF but low void plywood weighs less. If this
was a spare tire enclosure you would have a basic square that would come up
flush with the top of the enclosure. Double check and then double check
again on your measurements. Once you have the glass on this if you were off
you will have to start right over. You also want to make sure that the
fiberglass (or resin) will not be able to run into little nooks that will
get your enclosure stuck in your car. Seen it happen before when the tire
well's base was a little larger than than the opening. This guy did 7 layers
before he tried to pop it out. LOT's of cursing and frustration.
PIC 3:
This picture shows the first few layers of glass going down in the car. On
my first layer I used glass weave. I used a big chunk and stapled it to the
MDF so that it wouldn't go anywhere. Resin is very sticky and can "grab" the
mat and try to lift it. After the first layer was soaked I started using
chop mat to cover and soak up the remaining resin. It doesn't matter how many layers you do at once
but I would suggest doing one at a time if you've never used glass before.
Resin mixtures vary according to temperature and humidity and until you get
used to that it will waste a lot less resin if you mix a big batch and it
cures before your done layering. I do a gallon at a time for this part
because the resin pools a bit but let's me drop a LOT more mat down to soake
it up. Going with thicker layers also lets you mix the resin a little bit
cooler because there will be more of it trying to cure at once.
PIC 4:
This pic skips over a bit. As you can see the bottom portion of my enclosure
is finished. I went to about a 1/4" before I popped it out of the car.
Because I used the foil/tape barrier it simply lifted out. If this was a
spare tire enclosure you would now just have to attach your top board to the
frame and mount your sub. I'm going a little further with this one though.
I've cut rings for my subwoofers and used dowel to hold them where I want
the subs to be. Make sure that the rings are very solid. The fleece will
pull really hard on them. I used high temp hot glue to hold them in. That
square board is where my port for SPL will be. When you do the ring thing
double check IN THE CAR if you will have clearance! Add about a 1/4"-1/2"
around the rings for clearance because there will be fiberglass there.
PIC 5:
This pic shows the fleece stretched over the rings now. It also shows the
first layer of resin. I did two coats of resin on this one. The resin I used
was very thin otherwise one coat is usualy sufficient. You can tell when the
resin cures if there are soft spots. If there are soft spots you can mix a
small batch and recoat the spots. I stappled the fleece on to the enclosure
with about 3/4" spacing. Make sure that your fleece doesn't have any runs in
it when you stretch it around the rings.
PIC 6:
This pic skips through about 8 layers of glass. I usualy try to get a
thickness of around a 1/4" but there is a large flat surface on the top of
this box so I went to about a 1/2" thick on the top. Fiberglass is stronger
in curves so keep this in mind when you buld your enclosure. This box was a
PITA to do. We were going through a heat wave and the temps were around 45C
with humidity. In this heat you have about 1.5-2min to work in unless you
mix the resin really cool. On the third or fourth layer I mixed a little too
hot and the resin cured REALLY quick. I didn't have time to push out the air
bubbles and you can see a few of them. This isn't a problem as you just have
to grind them out (you can see an area along the back of the box were this
was done) with a Dremel tool or the like. Air bubbles can be difficult to
work out in such a short space of time. I use a pick and a 3" brush with the
bristels cut down to about a 1/2". I stab the bubble with my left hand and
push the air out with the brush in my right hand. Oh yeah, on the first
couple of layers you may find it hard to get the mat to hold unless it's on
a horizontal surface. I usualy put resin down and then put the layer on top
of it pushing it on with the brush. It may take a few tries to get this
right but you will get the hang of it. You can use a spray adhesive to hold
the mat and them resin over it but I find it unecesary once your use to it.
PIC 7.
Here is a pic of the first layer of Bondo. I use lighweight filler on stuff
like this Not much to say here but that your in for a lot of sanding. I find
with filler your better to start with thin layers and work your way up. If
you go with a thick layer you risk cracking the filler. Those black spots
are the fiberglass layer underneath. You can see from this that it doesn't
take a lot to make it look smooth. I had to do the sanding by hand and it
took a long time. I actualy havent got it finished yet. I threw a quick coat
of paint on it 'cause I was dying to hear it and if I had finnished it first
I wouldn't have had time to get it in this year. An air sander will save you
TONNES of time sanding a project like this.
PIC 8:
This shows the unfinished box in the Swift. It's got a coat of black on it
so you can see the little flaws that will get sanded out this winter. After
that it will get painted in a spray booth and will look like a mirror. You
can also see that with this box I have all the cargo space I would have with
the back seat up and my spare tire still (I can still squeeze my mountain
bike there!). With the carpet on the box it looks just like the rear seat is
in through the tint. Sounds awesome and there is now a port in it that's
tuned to 25Hz. With only 700W going to it I'm guessing I'm in the low to mid
140's. This may not sound like much for a pair of 15's but it's with a very
low tune. Going to an SPL tune will have this sytem in the low 150's with
the amp at 1 Ohm pushing around 2000W.
I'll have another FAQ coming up in the next little while on building door pods too. Hope this was helpful for a few people.
Later
Andre
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. The box came out after a summer when I changed cars and went to the scraper...