In this
guide we will build on the skills and techniques you learned in the " Intro To
Fiberglass Speaker box" DIY. This time we will be addressing the
concerns that come up when mounting larger subs and amps. This box is built to house a RE Audio XXX18 D2 speaker from: Audio
Savings
Because of the massive size of this speaker, we cannot simply build a
floor mounted box like before. The 15" of mount depth will
require the speaker and box to be recessed into the floor. In most
vehicles the spare tire well makes a perfect candidate. As a word of
caution, if you do remove your spare tire, you will want to carry a few
cans of Fix-A-Flat in its place. Start by removing the carpet and tire from the trunk, as well as any
miscellaneous liners that may be under the spare tire. If your tire well is
completely smooth you can skip the next step and go directly to mold
release.
In my case, the 850 tire well has several miscellaneous bolts and
fasteners located in the well that I did not wish to remove. Instead, I
taped over the entire well, allowing the tape to "tent" over any
protrusions. Start in the center of the well building tape layers as
you come up the sides. This is important as if you start at the top
your layers will overlap in a manor that allows resin to drip under the
tape should it decide to lift.
With the tape applied to the well and the area extending 2" past the
edges, apply 2-3 light layers of mold release. A spray gun is faster,
but in this application a brush or roller are also fine. After ~2 hours
you will have a dry mold release layer that is ready for resin.
Applying the mold release is an important often skipped step which will
be discussed later.
For boxes of this size
I alway suggest knit bi-axial fiberglass (KBF). KBF is a heavyweight
reinforcement material which is composed of two layers, a mat
layer stitched to a heavy cloth layer. KBF allows very strong
structures to be built, often with just a single layer. Cut several smaller,
~1 square foot, pieces of KBF before you mix your resin. This
fabric is thirsty, so take that into account when potting your resin.
Allow at least 10 minutes of working time and 10oz of resin
per sq/ft of fabric. With traditional fabric you apply a resin layer to
the mold, then lay out the fabric working out air pockets and assuring
proper wet out. Due to KBFs multiple heavy layers this technique will
not work. Instead I find it best to fold the cut piece of KBF and
completely submerge the cloth in the resin pot. This assures complete
wet out. Excess resin can be removed after the fabric is spread out.
Following the
technique described above, line the previously taped wheel well with a
single layer of KBF/resin. If you are not out doors, be sure to wear a
respirator while the resin is curing. Since you are using KBF not
traditional mat, 1 layer is all that is needed. In fact, this one layer
will probably support your body weight without additional
reinforcement. Once the resin has cured, (~45 minutes they way I pot
mine), you can begin removing the shell that you just cast. I find
that dissolving the mold release by prying up the edges and applying a
little water, aids in the separation of the mold and shell.
With the shell
removed, peel off any tape that came out with it. You should also take
this time to remove any tape left in the wheel well. A little warm
water will dissolve the mold release making this a quick task. You do
not want any tape left behind on the shell since it can lead to
delamination and makes for a less structurally sound box.
With the bottom shell
complete now turn your attention to the speaker rings. Because of the
XXX18's deep mounting depth and heavy weight, I decided against
suspending it only on a MDF ring with no additional support. Instead, I
settled on an inner skeleton to bear the compression weight created by
the speaker. Using MDF as an anchor, I installed six 1/2" rods cut to 15.25"
to support a two piece upper speaker ring. The upper ring having 1"
aluminum inlays to prevent the rods from pressing though from cyclic
loading.
In the last DIY we
used a Roto-Zip and a DIY guide to fabricate 12" rings. While the same
system would work here, a router and circle jig are much easier on a
ring this size. Start by cutting a circle 3" larger than your speaker
or 3" larger than your speakers mounting ring in the case of a recessed
speaker ring. In this case a 23" circle was cut, followed by a 19"
circle, leaving a 23" hoop. These steps were repeated using the
measurements 23" and 17.4" to complete the lower/inner speaker ring.
Using a drill press
and a circle cutter now fabricate six 1" inlays out of any thin bar
stock. Homedepot and Lowes sell 0.18" bar stock for only a couple dollars
per foot. Now using a 1" forstner bit and a microstop, set for the
thickness of your bar stock, drill six holes into the upper MDF ring. The holes should be
drilled at 0-60-120-180-240-300 degrees on a 21" radius. Label them at
this time so you can correctly clock the rings later on. Using a dab of
glue secure the inlays and set the upper ring aside.
On the lower ring,
using the same 0-60-120-180-240-300 in 21" pattern, drill a 1/2" hole
all the way through the ring and label the holes.
Apply a liberal layer
of wood glue to the bottom of the top ring and the top of the bottom
ring
and clamp them together once the 6 holes are properly aligned. Now from
the bottom install 1" wood screws every 4". Pre-drill where
you intend to install the wood screws using a 1/16" bit to avoid any
splitting. To clean things up
as well as ease the MDF to fiberglass transition round off the two
upper ring edges using a 1/2 self guiding round over bit.
With the ring complete
you should now take all the parts back to the car and double check the
fitment. This is the last chance you will have to make any small
adjustments you may need to make.
With everything double checked, install all 6 rods and wrap the box in
the fabric of your choice. As discussed earlier, I prefer a light
cotton but many prefer fleece. Before you continue, make sure the rings
are pressed all the way down onto the rods. With the box wrapped, apply
a light coat of resin as discussed in the earlier DIYs. Once the resin
has cured, cut away any excess fabric and begin building the upper half
of the shell in fiberglass. At this stage I use any extra resin I have
left over to seal the "seam area". Before the resin has a chance to
cure simply pour it into the box and sand the box on end so the resin
collects at the seam. Rocking the box will assure all areas are coated
and sealed.
As before, the level
of finish the box requires, depends on if you plan to paint or carpet
it. No matter what finish you opt for, the box will require at least
one
application of filler to correct any seams or contour lines left
by the fiberglass. Some people like to use a technique called
"Milkshaking". Milkshaking is using 1 part mixed filler with 2 parts
mixed resin to create a "milkshake". This sludgy mix is what some
people use instead of a proper glazing puddy. I normally do not
use this
technique since I find it easier to work with filler and I
believe it is structurally superior. Thanks in part to the internal
skeleton,
this box weighed only 38 pounds, and was strong enough to support
hundreds of pounds (my weight standing on it) without any problem.
Using this technique a
box that could house even the heaviest MTX Jackhammer's could be
fabricated and still weigh significantly under 100 pounds.
Because this
intermediate guide is leading up to the expert guide, I went with a
simple truck bed liner finish on the box. The finished result is a box
that is clean and utilitarian. With the carpet installed back around
the box, the look is industrial but finished. In the next guide we will
cover advanced techniques such as completely glassing in the trunk and
utilizing recessed and hidden amp racks.
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