Automotive Subwoofers Owner’s Manual GT100 GT100D GT120 GT120D GT150 GT150D
GT SERIES
™
Thank you for purchasing a
new JBL GT Series subwoofer.
Subwoofer installation requires
woodworking skills and some
experience disassembling and
reassembling automotive interiors.
If you lack the tools or necessary
skills, have your subwoofer installed
by an authorized JBL dealer.
Warning: Playing loud music in
an automobile can permanently
damage your hearing as well as
hinder your ability to hear traffic.
We recommend listening at low
levels while driving. JBL accepts no
liability for hearing loss, bodily injury
or property damage resulting from
use or misuse of this product.
GT Series subwoofers are optimized
to perform best in small, sealed,
vented and prefabricated bandpass
enclosures. While infinite-baffle
mounting of GT Series subs is
possible, power handling will be
greatly compromised because
there’s no enclosed volume of air
to prevent the speaker’s cone from
moving past its limit. For this reason,
we do not recommend infinite-baffle
mounting for GT Series subwoofers.
You should choose the enclosure
you will use based on the type of
music you listen to, how much
amplifier power you will use for the
subwoofer and how much space
inside the vehicle you can devote
to a subwoofer 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 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 and there are
many prefabricated sealed
enclosures available. An optimum
sealed enclosure is always smaller
than other types of enclosures
optimized for a particular speaker,
so they require the smallest amount
of space inside the vehicle.
Vented enclosures provide better
efficiency in the 40Hz –50Hz range
but this efficiency comes at the
expense of sound in the lowest
octave (below 40Hz) and at the
expense of some control and power
handling. 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. While
there are some prefabricated
vented boxes available, matching a
prefabricated box to a particular
woofer is difficult. 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 often
provide the most 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 bandpass
enclosure. Bandpass-enclosure
design is very tricky and the aid
of a computer and enclosure
design software is necessary. If
you are an experienced installer
or have some woodworking
experience, you may wish to build
the enclosure described in the
enclosure design sheet included
with this woofer. Fortunately, there
are many prefabricated bandpass
boxes available and they are all
optimized to extract the most
output possible from any woofer.
Bandpass enclosures can be quite
large and may require a lot of space
inside your vehicle.
02
Choosing an Enclosure JBL GT Series
03
Connecting Your Subwoofer to Your Amplifier JBL GT Series
JBL GT Series subwoofers
are available in two different
configurations: as a single 4-ohm
voice coil or as dual 4-ohm voice
coils. Depending on the amplifiers
you are using, you may use either
single-voice coil or dual-voice coil
subwoofers in singles or multiples
to maximize the power available
from your amplifiers. To achieve
the maximum amplifier output
possible, you should design a
speaker system that provides
the lowest impedance that
your amplifier is rated to drive
safely. When designing a
subwoofer system, consider
the following rules:
1. Don’t mix different subwoofer
or enclosure types in the same
system (use all single-coil
woofers or all dual-coil woofers).
2. You may connect the coils of a
dual-voice coil woofer in series,
but we recommend that you
avoid connecting separate
woofers in series. The amplifierdamping factor (the amplifier’s
ability to control the motion of
the woofer) is expressed as a
ratio of terminal impedance
(the sum of speaker impedance,
wire resistance and the D.C.
resistance of any crossover coil
connected to the woofer) to
amplifier-output impedance.
Therefore, connecting separate
woofers in series reduces the
damping factor of the amplifier
to a value less than 1. This will
result in poor transient response.
3. You must use both coils of a
dual-voice coil woofer connected
either in series or in parallel.
4. Most amplifiers deliver exactly
the same amount of power
bridged into a 4-ohm load
as they do running a 2-ohm
stereo load.
To design a subwoofer system
that maximizes available amplifier
power, keep the following rules
in mind:
1. The total system impedance
of woofers in parallel can be
calculated using the formula:
Impedance =
1
1+1+1
...
w1w2w
3
where w is the nominal
impedance of the woofer.
2. The total system impedance
of voice coils (or woofers) in
series can be calculated using
the formula:
Impedance = w1+ w2+ w3...
The diagrams at right show parallel
and series speaker connections.
Figure 1. Parallel connection
POS ( + )
NEG ( – )
RED
STRIPE
POS ( + )
BLACK
STRIPE
NEG ( – )
Figure 2. Series connection
POS ( + )
NEG ( – )
RED
STRIPE
POS ( + )
BLACK
STRIPE
NEG ( – )
GT100 GT100D GT120 GT120D GT150 GT150D
10" Automotive 10" Dual-voice coil 12" Automotive 12" Dual-voice coil 15" Automotive 15" Dual-voice coil
subwoofer automotive subwoofer subwoofer automotive subwoofer subwoofer automotive subwoofer
Power handling (RMS) 250 Watts 250 Watts 250 Watts 250 Watts 250 Watts 250 Watts
Power handling (Peak) 1000 Watts 1000 Watts 1000 Watts 1000 Watts 1000 Watts 1000 Watts
Sensitivity (2.83V/1m) 90dB 90dB 93dB 93dB 95dB 95dB
Frequency response 28Hz – 500Hz 28Hz – 500Hz 23Hz – 450Hz 23Hz – 450Hz 20Hz – 400Hz 20Hz – 400Hz
Impedance 4 Ohms Dual 4-ohm voice coils 4 Ohms Dual 4-ohm voice coils 4 Ohms Dual 4-ohm voice coils
Mounting depth 5-3/4" (147mm) 5-3/4" (147mm) 6-1/4" (159mm) 6-1/4" (159mm) 6-3/4" (172mm) 6-3/4" (172mm)
Cut-out diameter 9-1/8" (232mm) 9-1/8" (232mm) 11-1/8" (283mm) 11-1/8" (283mm) 14-1/4" (362mm) 14-1/4" (362mm)
JBL Consumer Products • 250 Crossways Park Drive, Woodbury, NY 11797
1.800.336.4JBL (4525) • www.jbl.com
Features, specifications and appearance are subject to change without notice.
©2002 JBL, Incorporated • JBL is a registered trademark of JBL, Incorporated
Part No. GTSUBSEROM
Specifications JBL GT Series
Declaration of Conformity
We, Harman Consumer International
2, route de Tours
72500 Chateau-du-Loir
FRANCE
declare in own responsibility, that the products described in this owner’s manual are in
compliance with technical standards:
EN 50081-1:1992
EN 50082-1:1997
Emmanuel Millot
Harman Consumer International
Chateau-du-Loir, FRANCE. 7/02
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