8
0
0
.
4
1
0
0
0
.
4
1
2
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4
1
5
0
0
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4
1
8
0
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4
G
T
i
”
By sending in
cone motion is controlled by a synthetic rip-stop
suspension which resists tearing for safe, effortless
high-power use. The cone is driven by a massive
motor structure utilizing a 3" or 4" edge-wound
OFC copper wire, high temperature fiberglass,
voice coil. This motor structure includes JBL’s
patented Symmetrical Field Geometry (SFG) to
create a uniform magnetic flux field through the
coil and thus lower distortion. The frame and cone
are contained in a high strength die-cast aluminum
frame for maximum rigidity and higher magnetic
energy concentration on the coil.
What does all this technology add up to? A
driver with smooth frequency response, excellent
transient response, high output efficiency and high
power handling in a rugged package able to deal
with the rigors of high performance car audio. The
result is exceptionally powerful, dynamic and accurate sound reproduction that cuts through the road
noise and provides a solid musical foundation.
Unleash Maximum Performance
Because this is a high performance product
which may be used in many different configurations, we strongly recommend that you have the
subwoofer professionally installed to unleash its
full performance potential. However, if you feel
you have the skills necessary to build a subwoofer
box, read the following information on enclosures
before proceeding.
Enclosure Basics
The enclosure you build plays a profound role in
the performance of your subwoofer. The size and vent
tuning frequency, where applicable, determine the
low-frequency performance and output capability of
the subwoofer system. Your GTi subwoofer will provide excellent performance when used in Sealed,
Vented, Infinite Baffle, and Band-pass applications
that are properly designed. Each of these applications
have limits and advantages that should be considered.
GTi woofers are most commonly used either in
Vented enclosures or Infinite Baffle. Instructions which
follow will give you a simplified design method to build
a Vented enclosure for your subwoofer. Another
option is the Infinite Baffle (free air) installation which
doesn’t require complex design and construction, and
can sound very good when solidly installed. However,
because there is no enclosure to control cone motion,
the power handling and maximum output level of an
Infinite Baffle installation is reduced from that of a
Vented enclosure. Refer to the “Points on Power
Handling” section for more information.
For more complex designs, such as single and
dual-vented Band-pass types, we suggest you optimize your design with JBL SpeakerShop, a speaker
system design software for a P.C. running Microsoft
Windows, available from your JBL dealer. If JBL
SpeakerShop or a similar program is not available,
the JBL Customer Service department will be happy
to assist you.
3
3
2
3. Now that you have calculated the internal box
volume, you should subtract the DRIVER DISPLACEMENT (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 displacement of the port tube by utilizing the formula 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 corresponding tuning frequency. We have drawn an
example on the chart.
5. Use the Port Nomograph on the Driver Specification 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 construction 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 construction tips listed on page 6.
5
l
over excur-
Speaker Connection
and Combination
GTi subwoofers are 4 ohms nominal impedance. If you are connecting two speakers in
parallel to an amplifier channel, make sure your
amplifier will drive a two ohm load.
If your amplifier
will not drive a
two ohm load, we
recommend that
you connect the
two speakers in
series to create
an 8 ohm load as
shown here.
Four woofers can also be wired (as shown below)
in parallel/series or series/parallel so that the
amplifier will see four ohms nominal impedance.
Please consult your JBL dealer for information on
more complex speaker combinations.
7
–
+
–
+
(+)
2 ohms
Nominal
Impedance
(–)
–
+
–
+
(+)
(–)
8 ohms
Nominal
Impedance
Parallel Wiring
Series Wiring
Parallel/Series
Wiring
Series/Parallel
Wiring
4 ohms
Nominal
Impedance
–
+
–
+
(+)
–
+
–
+
(–)
4 ohms
Nominal
Impedance
–
+
–
+
(+)
–
+
–
+
(–)
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