Check with manufacturer
or dealer for appropriate box volume and design. Some subs can't be used in certain
types of boxes, and have very small tolerances for box volume errors. If a sub is
installed in a box larger or smaller than what is supposed to, it will sound bad and could
be destroyed. Boxes can be built in any shape, but it is difficult to calculate
volume for complex shapes.
Materials
A box has to be very rigid. Most common building materials are
5/8" or thicker particle board or medium density fiberboard.
If building a box with Plexiglas, do not use anything less that 1/2
inch thick.
A common material used to mold complex shaped boxes is fiberglass,
but it is a real pain to work with, and several layers need to be applied for a solid
finish.
Gluing, Sealing
Use glue at all joints (cheapest and most used product is Liquid
Nails). Make sure there are no holes. Any leaks will degrade the performance
of your subs, not to mention the annoying noise air makes when being pushed out of a small
hole.
Let glue cure for at least 24 hours before mounting the
woofers. The fumes of some products will eat up rubber and other materials subs are
made of.
Holding Joints Together
Screw joints (use 2" - 2-1/2" screws) every
four inches or so. Pre-drill about 3/4" deep, so that screws do not split the wood at
the edges, especially when working with particleboard.
A box for Each Sub?
Even though it is not necessary to have two separate chambers for
two subs, it is best to take this approach for two reasons: First, if one of the
subs dies, then the volume of the box will be "twice" as big, as seen by the sub
that is still working. This could cause problems and even damage the other sub.
The second reason is bracing. building a box with a divider in the middle
will be much sturdier.
Making Ports
There are several way to build ports. If a pre-made port is
not available, the most common material is PVC tubing. PVC tubing is very rigid,
comes in different diameters, and is easily found at any hardware store.
Cut the tubing at the desired length. Consider the volume the
port takes up when calculating the box volume. Cut a hole in the box. Make
sure the hole is as perfect as possible to minimize gaps between the box and the tube.
A couple wood braces can be added for screwing the port top the box. Seal the
gaps using plenty of Liquid Nails or similar product.
Bracing
Boxes that are more than a foot on width or length or height, should
be braced (use a piece of wood maybe 3 or 4 inches wide across the box, so that box does
not flex). It is a good idea to put wood blocks on the corners for reinforcement.
Always consider that blocks, braces, neon lights, etc. inside a box take up space and
should be accounted for when calculating internal volume.
Damping/Filling
It is advisable to put damping material inside a box. Pillow
polyfill and fiberglass insulation are common, though polyfill is a lot easier on your
skin. This increases subwoofer efficiency by dissipating some energy that affects
the sub, particularly the voice coil. Polyfill also "fools" a sub into
thinking it is in a bigger box. Play around with different amounts of polyfill until
you get the desired results.
Finishing the Box
Add wood filler to holes and sand the box to make a smooth
surface. If you are painting the box, It is a good idea to apply primer under the
paint.
It is not necessary to sand the box if you are using carpet or
padding under vinyl, since the thickness of the material will cover any small
imperfections. The best way to cut carpet or vinyl is with a good quality carpet
knife. Blades wear out pretty quickly, so buy a handful. Cut a piece of carpet
(or vinyl) big enough to cover the whole box. Apply adhesive to both box and carpet
(spray 3M adhesive 77 or 90 works great). Wait about a minute and place the fabric over
the wood. For a good fit, stretch the fabric when applying it. The fabric
should wrap around and end in a place of the box that will not be seen. Do one side
at a time, cutting excess carpet. If possible, add staples to hold the fabric at the
ends.
