TM
PROPOWER
Automotive Subwoofer Owner’s Manual W10GTi W12GTi W15GTi
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Choosing an Enclosure
Because a sealed enclosure provides the
most control over the woofer’s movement, a
woofer mounted in a sealed enclosure will
handle more power at low frequencies than
a woofer mounted in another enclosure
type. Sealed enclosures provide more
accurate sonic reproduction than other
enclosure types, so they are well suited
to all types of music. Sealed-enclosure
construction is straightforward. An
Vented enclosures provide better efficiency
in the 40Hz – 60Hz range, but this
efficiency comes at the expense of sound
output in the lowest octave (below 40Hz)
and at the expense of some control and
power handling below box tuning. If you
are using a small amplifier, a vented box
will provide more bass output from less
power. Vented enclosures are also well
suited to a variety of music types. Because
vented enclosures require the volume
of the enclosure and the size of the port
to have a specific relationship with the
characteristics of the woofer, the enclosure
must be built exactly to the specifications
provided. If you wish to use a vented
enclosure, we strongly recommend having
your authorized JBL dealer build it; or
verify that your design is correct if you
wish to build it yourself. An optimum
vented enclosure is always larger than
the optimum sealed box for the same
woofer, and will require more space
inside the vehicle.
Bandpass enclosures can provide the
greatest output available from any amplifier
and subwoofer combination – at the
expense of sonic accuracy. If sheer SPL
(sound pressure level) is what you desire
most, choose a vented or bandpass
enclosure. Bandpass enclosure design is
very tricky and the aid of a computer and
enclosure design software is necessary if
you wish to design the enclosure yourself.
Like a vented enclosure, a bandpass
enclosure must be built exactly to the
specifications provided. Bandpass
GTi Series subwoofers are optimized to
perform best in small sealed, vented and
bandpass enclosures. While infinite-baffle
mounting of GTi Series subs is possible,
power handling will be compromised since
there will be no enclosed volume of air
to help the speaker’s suspension control
the motion of the woofer’s cone. For this
reason, we do not recommend infinite-
baffle mounting for high-power applications.
optimum sealed enclosure is always smaller
than other types of enclosures that are
optimized for a particular speaker, so they
require the least space inside the vehicle.
You should choose the enclosure you’ll use
based on the type of music you listen to,
how much amplifier power you’ll use to
drive the subwoofer, and how much space
inside the vehicle you can devote to a
subwoofer enclosure. If you’ll be using your
GTi Series subwoofer for SPL competition,
please see the document titled “GTi as SPL
Competition Subwoofers” (included with
your woofer).
enclosures can be quite large and may
require a lot of space inside your vehicle.
03
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The Official Brand of Live Music
®
Enclosure Construction
5. Use PVC or ABS plastic pipe for ports.
Keep in mind that the openings at either
end of the port must be at least one port
diameter away from any obstruction.
6. Use the 10/24" machine screws and
T-nuts provided to mount the woofer to
the baffle. See Figure 1.
Dual Coil Versus Differential Drive
(patent pending)
Figure 2. Conventional dual-voice-coil design
Please observe the following suggestions
when building an enclosure for GTi Series
subwoofers.
1. Choose an enclosure design from the
Enclosure Design Sheet included with
your subwoofer.
Conventional dual-voice-coil woofers use
a pair of voice coils “interwound” on the
former and centered in the magnetic gap.
The two coils may be connected in series
or parallel in order to maximize an
amplifier’s output power. Both coils drive
the cone forward and rearward. Xmax
(one-way-linear) is determined by the
amount of voice coil exposed above
and below the top plate. A conventional
voice coil is made up of several layers of
windings, each transferring heat to the
winding next to it until the heat is finally
dissipated by the outside layer through
the top plate, magnet and backplate. This
arrangement is inefficient, and results in
low thermal power handling. See Figure 2.
CONE
BOTH COILS
SPIDER
DRIVE CONE
FORWARD
AND
2. Use at least 3/4" (19mm) MDF (medium
density fiberboard) or marine birch
plywood to build the enclosure.
Enclosures for 12" and larger
subwoofers and smaller woofers driven
by high-power amplifiers should be
constructed using 1" (25mm) material.
3. Join pieces of wood with glue and
screws; do not use nails. Once the box
has been tested, seal all joints inside
the box with silicone caulk.
4. Fill the enclosure with damping material
(dacron, fiberglass insulation or
long-fiber wool) according to the design
you have chosen from the Enclosure
Design Sheet. “0% fill” indicates
that no damping material
OVERHANG DETERMINES
Xmax
REARWARD
TOP PLATE
MAGNET
POLE PIECE / BACKPLATE
Figure 1. Mounting the GTi woofer
in its enclosure
JBL GTi Series subwoofers employ
Differential Drive, a technology developed
by JBL Professional. Differential Drive
employs two voice coils positioned at
opposite ends of the former, each
suspended in a separate magnetic gap.
These two coils may be connected in series
or parallel, like a conventional DVC woofer,
to maximize an amplifier’s output power.
Both coils MUST be connected to the
amplifier in correct polarity! At low power,
both voice coils drive the woofer’s cone,
and any motor nonlinearities are cancelled
by the out-of-phase coils and gaps. As
power input increases so that one coil rides
completely out of its gap, force is still
applied to the cone by the other coil. At
extremely high power, each coil will enter
should be used; “50% fill”
indicates that all interior walls
except the baffle should be
lined with 1" thick damping
material, and “100% fill”
indicates that the box should
be loosely stuffed with
damping material.
10/24"
SCREWS
(PROVIDED)
T-NUTS
(PROVIDED)
04
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TM
PROPOWER
Figure 5. Connecting the voice coils in
parallel (3 ohms)
the other coil’s magnetic gap. This will
cause magnetic braking, which will slow
the cone’s motion and prevent damage
due to overexcursion. For a GTi Series
woofer, Xmax is determined by the amount
of voice-coil overhang between the first
and second top plates. See Figure 3.
Thermal power handling is far superior
to a conventional DVC woofer using
voice coils of a similar diameter and
length because Differential Drive provides
twice the heat-dissipating surface area
and two top plates to transfer heat to
the magnet-cover fins.
Connecting Your Subwoofer to
an Amplifier:
Note: Unlike conventional DVC
subwoofers, the two sets of terminals
are configured so that both positive (+)
terminals are on one side of the frame
and both negative (–) terminals are on
the other side. GTi Series subwoofers are
shipped with terminal jumpers installed
which configure the two 6-ohm voice
coils in parallel for a 3-ohm load.
Note: Connect the coils in parallel if you are
connecting a single woofer to an amplifier.
Configuring the voice coils:
TERMINAL
JUMPER
INTACT
TERMINAL
JUMPER
INTACT
Figure 4. Terminal locations
RED
BLACK
TERMINAL
TERMINAL
Note: Both voice coils MUST be
connected to the amplifier in series
or parallel.
+
Figure 6. Connecting the voice coils in
series (12 ohms)
Figure 3. JBL dual-gap design
CONE
TERMINAL
JUMPER
REMOVED
TERMINAL
JUMPER
REMOVED
TOP COIL
IN GAP #1
DRIVES CONE
FORWARD
SPIDER
RED
BLACK
TERMINAL
TERMINAL
1st
GAP #1
GAP #2
TOP PLATE
MAGNET
POLEPIECE
OVERHANG
DETERMINES
Xmax
+
2nd
TOP PLATE
BOTTOM COIL
IN GAP #2
DRIVES CONE
REARWARD
ALUMINUM
COVER
05
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The Official Brand of Live Music
Configuring multiple woofers for
connection to a single amplifier:
Figure 7. Connect two woofers in parallel
(with coils in parallel) for a 1.5-ohm load
Figure 8. Connect three woofers in parallel (with
coils in series) for a 4-ohm load
Figure 9. Connect four woofers in parallel (with
coils in series) for a 3-ohm load
TERMINAL
JUMPER
REMOVED
TERMINAL
JUMPER
REMOVED
TERMINAL
JUMPER
REMOVED
TERMINAL
JUMPER
REMOVED
BLACK
TERMINAL
RED
TERMINAL
BLACK
TERMINAL
RED
TERMINAL
TERMINAL
JUMPERS
INTACT
TERMINAL
JUMPERS
INTACT
RED
BLACK
TERMINAL
TERMINAL
+
+
06
+
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PROPOWER
Specifications
W10GTi
W12GTi
W15GTi
10" Automotive subwoofer
12" Automotive subwoofer
15" Automotive subwoofer
Power handling (peak)
Power handling (avg.)
Frequency response (in-car)
Impedance
3000W
4000W
5000W
600W
700W
800W
20Hz – 1kHz, 3dB
3 or 12 ohms
18Hz – 1kHz, 3dB
3 or 12 ohms
16Hz – 1kHz, 3dB
3 or 12 ohms
Sensitivity (2.83V/1m)
Overall diameter
90dB
91dB
92dB
10-1/2" (267mm)
12-1/4" (312mm)
15-1/4" (388mm)
Cut-out diameter
Mounting depth
9-3/16" (234mm)
9-1/8" (232mm)
.108 cu. ft. (3.06 L)
11" (280mm)
13-7/8" (353mm)
10-1/4" (260mm)
.174 cu. ft. (4.93 L)
10-1/4" (260mm)
.149 cu. ft. (4.23 L)
Basket displacement
07
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Declaration of Conformity
We, Harman Consumer International
2, route de Tours
72500 Chateau-du-Loir
FRANCE
JBL Consumer Products • 250 Crossways Park Drive, Woodbury, NY 11797
declare in own responsibility, that the products described in this owner’s manual are in
compliance with technical standards:
©2000 JBL, Incorporated • JBL is a registered trademark of JBL, Incorporated
EN 50081-1:1992
EN 50082-1:1992
Made in USA Printed in USA 9/00
Part No. W10,12,15GTIOM
Lutz Uphoff
Harman Consumer International
Chateau-du-Loir. FRANCE. 9/00
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