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Enclosure Design
Follow the simple steps below to design an
optimum ported box for your GTi driver.
1. Determine the maximum enclosure size
available for your installation by measuring
and multiplying the height x width x depth (in
inches) and then dividing by 1728. This will tell
you exactly how many cubic feet your enclosure
will be.
2. To determine the volume of an irregularly
shaped box, divide the box into sections, calcu-
late the volume of each section individually, then
add the separate volumes to determine the total
box volume. Here are some useful formulas to
help you calculate volumes:
USEFUL FORMULAS
1 cubic foot = 1728 cubic inches
1 cubic foot = 28.32 liters
1 liter = 0.353 cubic feet = 61 cubic
inches = 1000cm
3
Radius = 1/2 diameter
Box volume = height x width x depth
Volume of triangular box section = 1/2 base x
height x length
Volume of tubular duct = area of circle x length
pi (π) = 3.1416
2
Area of circle = pi (π) x radius
Diameter of circle = 2 x area / pi (π)
Area of square = height x width
3. Now that you have calculated the internal box
volume, you should subtract the DRIVER DIS-
PLACEMENT (listed on the specification sheet)
while also subtracting approximately 0.1 cubic
feet for the port tube (if one is being used). If
you'd like, you may calculate the exact dis-
placement of the port tube by utilizing the for-
mula listed above (Volume of tubular duct).
4. Using the GTi Enclosure chart (shown on your
GTi driver specification sheet), choose a desired
box volume on the vertical chart axis, which fits
within the size limit you have established. Draw
a line across from this point until it intersects the
recommended tuning frequency. Draw a line
down to the horizontal axis and read the corre-
sponding tuning frequency. We have drawn an
example on the chart.
5. Use the Port Nomograph on the Driver Specifica-
tion sheet to determine the port diameter and
length based on the enclosure volume and tuning
frequency determined in step 4. Follow these
steps to determine the port.
Port Dimension Calculation
1. Draw a line from the chosen enclosure volume to
the desired tuning frequency. Continue this line
until it intersects with the Lv/Sv construction line
(Lv = port length, Sv = port opening surface
area). This is called the construction point.
2. Draw a horizontal line starting from the con-
struction point straight through the chart. Note
that the Lv/Sv axis also appears at the right of
the chart to help keep your line parallel all the
way across the chart.
3. Select the curved line with the port diameter
you would like to use. Locate the point where
this curved line intersects with your horizontal
construction line and draw a vertical line from
this point down to the bottom of the chart.
NOTE: Try to use a port tube no smaller than 1/3 the
diameter of your speaker. Using a smaller diameter
port can result in "whistling" or "breathing" noises.
4. The required port length is found at the point
where the vertical line you've drawn intersects
with the scale at the bottom of the chart.
NOTE: The recommended port tube dimensions
should be considered a starting point. Since it is
impossible to predict "in-car" response exactly, you
may find that a port length slightly longer or shorter
than that recommended may produce slightly better
results. Experiment!
Lay out plans for your box using the information
determined in the above steps and the box con-
struction tips listed on page 6.
5
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