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Calculating Port Size

The box port can be calculated with a simple formula. Box volume in
cubic feet X 16 (the amount of port area in square inches per cubic feet
of box volume). For example, 3.4 cuft X 16 sqin= 54.5 square inches of
port area. Try to stay within 10% of this number.

The port length should be 16 inches deep. This tunes the boxes to about 40 Hz.

How To Make A Slot Port

The
easiest and most effective way to build a port is to use a slot shaped
port that uses 3 sides of your enclosure as port walls. If the port is
located at one end of the box, only one additional piece of wood is
required to complete the port. The additional piece of wood should be
spaced off the end of the box.

The port area is in square inches,
meaning it takes height times width to calculate total area. A port 4
inches high by 4 inches wide would calculate as 4 X 4= 16 square inches.

In
our example box, we have an inside height of 14.5 inches. To calculate
the slot width that would make a total area of 54.5 square inches, and
we use 14.5 inches as the height: divide 54.5 by 14.5= 3.76. Round that
figure to nearest ¼ inch, and you get an offset measurement of 3 ¾ inch
wide. The slot port would be 3 ¾ inches wide by 14 ½ inches tall.

You
don’t have to get too critical about the box and port volume, a good
rule of thumb is that if you stay within 5-10% of calculated volumes,
there will be very little if any audible effects.

Port Length Obstructions

Some
port lengths do not allow for 16-inch port depths without some sort of
modification. The rule of thumb is not to let the end of the port get
any closer to the back wall than the width of the port. So back to our
example, we have an internal box depth of 12.5 inches. We need a 16-inch
deep port. We will have to bend the port along the back wall to get the
full port length. To calculate where to make the bend, subtract the
port width from the inside box depth. 12.5 – 3.75=8.75. We must bend the
port at 8.75 inches, then continue the port parallel to the back wall
for an additional 7.25 (8.75+7.25=16).

You now have an L shaped port totaling 16 inches in depth.

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Calculating Box Volume

How To Figure Box Volume

Cubic feet is measured by
multiplying the height X width X depth of the inside dimensions of the
box, and dividing that total by the number of cubic inches in a cubic
foot (a cubic foot is 12 X 12 X 12= 1728).

For example, a box with
outside measurements of 16 inches high, by 34 inches wide, by 14 inches
deep would be figured as so; first we subtract the wood thickness. This
is usually ¾” thick, times the thickness of both sides of the box= 1 ½
inches. We subtract this from the outside dimensions.

So now we have
14.5H X 32.5W X 12.5D=5890.625.

5890.625 divided by 1728 = 3.4 cubic feet.

You
can keep changing dimensions and refiguring the box volume, until you
come up with the ideal box size and shape for your application.

5890.625 divided by 1728 = 3.4 cubic feet.
Calculating Net Volume:
The volume occupied by the woofer and port is approximately 18% of the
box. We need to deduct this volume from the gross volume of the box to
find the net volume. The port will be calculated on the net volume.
Now, take your 3.4 cubic feet and multiply by .82 (3.4*.82=2.788) so your Net Volume is 2.788 cubic feet.
Calculating Port Area:
Our port formula uses 16 square inches of port area per cubic foot of box volume.
Now, take your 2.788 cubic feet and multiply it by 16 so get your Total Port Area
2.788*16 = 44.608 sq” of port area.
Calculating Rectangular Port Dimension:
Port area needs height and width. For a rectangular box with known
dimensions, we already have a height, we just need to find the width of
the port.
Now, take your 44.608 and divide it by the height of your box, so this
example we would divide 44.608/16= 2.788 (this is width of your port
opening) Round it to the nearest .25”.
The “Average” recommended length of the port is 18”, tuning around 40hz.
The longer you make the length of the port, the lower the tuning. Those
that listen to nothing but hip/hop, rap and chopped & screwed, you
can make your port length 22-24” long.
**You can keep changing dimensions and
refiguring the box volume, until you come up with the ideal box size and
shape for your application.

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High Performance Enclosure

We don’t believe in the tiny sub box theory. If you are looking for
tiny sound, get a tiny sub and put it in a tiny box. Be happy. If you
are looking for real bass, you need to have a real box.

In order
to get true high performance, you have to make the most of the available
airspace you have. To do otherwise is wasting your time, energy and
money. Don’t try to fit a larger speaker in a box that is better suited
for the next size down. Our subs all have the same amount of throw, the
same force available, and the smaller sub in the right space will
outperform the larger sub in too small an airspace.

The first step
in getting major bass in your vehicle is to allocate the space for your
enclosure. If you really want to flex some sheet metal, the old adage
applies, “there is no substitute for cubic inches”. The more space you
make available, the higher the potential spl.

You don’t have to use a large amount of enclosure space to make a loud system; loud can be done with a single SoundQubed
sub. The amount of loud needs to be determined as you figure out what
space you plan to give up. Really loud bass, where you have to scream at
your passengers, can be done on a single or double woofer setup. Stupid
loud bass, where there is no point in trying to communicate in the
vehicle, takes more space and bigger/more subs. F@#$ing crazy loud bass,
where it is impossible for the car next to you to communicate inside
his vehicle, takes even more space, even more subs and a gazillion watts
of power.

A few tips on what to pay attention to when determining the box shape:

If
you plan to use a rear firing setup in a trunk car, make sure your box
doesn’t seal off the trunk from the passenger compartment. You need to
leave some space for the waves to pass back into the interior of the
car. Either make the box as low as possible so the wave passes over the
box and enters the cabin via the seatback and rear deck, or reduce the
width of the box so the wave can pass to the side and into the car’s
interior. A big, giant box may make your trunk extremely loud, but all
you’ll hear is muffled rattle if the box takes up the whole space behind
the rear seat and under the rear deck.

If you have a hatchback car, keep the box as far back in the vehicle as possible. Keep the port as far to the rear as possible.

Speaker Box Construction:

A strong box is essential in a high output system. Your box should be
free from air leaks and braced internally if the volume exceeds 2 cuft.
Internal cross bracing is far more effective in making a rigid box than
doubling the wood thickness. Doubling the wood thickness adds a great
deal of weight to your vehicle, and the added wall stiffness is less
than stiffness added by cross bracing. Try to cross the braces at the
same point so that they add strength to each other.

The inside
seams of the enclosure can be a source of air leaks and potential
weakness if the joints are not cut perfectly. One way to strengthen
these joints is to use gluing cleats on the inside seams.

 

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