P1242 - JBL Car Audio User Guide / Operation Manual

p1242 user guide / operation manual
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User Guide / Operation Manual
Car Audio

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Automotive Subwoofers Owner’s Manual 
P1040  P1042  P1240  P1242
Thank you for purchasing a new
JBL GTp 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.
GTp subwoofers are optimized 
to perform best in small, sealed,
vented and prefabricated bandpass
enclosures. While infinite-baffle
mounting of GTp 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 GTp 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.
Choosing an Enclosure 
JBL Pro Power GTp Series
JBL GTp subwoofers are available
in two different configurations: 
single 4-ohm voice coil and dual 
4-ohm voice coils. Depending on
the amplifier 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
amplifier. 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 NEVER connect separate
woofers in series. Because the
amplifier-damping 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, 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 = 1/(1/w
+ 1/w
...), where w is the
nominal impedance of the
2. The total system impedance 
of voice coils (or woofers) in
series = w
+ w
+ w
The diagrams below and at right
show parallel and series speaker
Figure 1. Parallel connection
Figure 2. Series connection
POS ( + )
NEG ( – )
POS ( + )
NEG ( – )
POS ( + )
NEG ( – )
POS ( + )
NEG ( – )
Connecting Your Subwoofer to Your Amplifier 
JBL Pro Power GTp Series
JBL Consumer Products • 250 Crossways Park Drive, Woodbury, NY 11797
1-800-336-4JBL (4525)  www.jbl.com
©2000 JBL, Incorporated • JBL is a registered trademark of JBL, Incorporated 
Made in USA   Printed in USA 3/00   
Part No. P1040-42/P1240-42OM
P1040 P1042 P1240 P1242
10" Automotive subwoofer
10" Automotive subwoofer,
12" Automotive subwoofer
12" Automotive subwoofer,
dual voice coil
dual voice coil
Power handling (peak)
1400 Watts
1400 Watts 
1400 Watts
1400 Watts
Power handling (RMS)
350 Watts
350 Watts 
350 Watts
350 Watts
Sensitivity (2.83V/1m)
Frequency response
20Hz – 500Hz
20Hz – 500Hz
18Hz – 500Hz
18Hz – 500Hz
4 Ohms
2 or 8 Ohms
4 Ohms
2 or 8 Ohms
Mounting depth
5-1/8" (131mm)
5-1/8" (131mm)
5-11/16" (145mm)
5-11/16" (145mm)
Cut-out diameter
9-1/8" (232mm)
9-1/8" (232mm)
11-1/8" (283mm)
11-1/8" (283mm)
JBL Pro Power GTp Series
Declaration of Conformity
We, Harman Consumer International
2, route de Tours 
72500 Chateau-du-Loir
declare in own responsibility, that the products described in this owner’s manual are in
compliance with technical standards: 
EN 50081-1:1992
EN 50082-1:1992
Lutz Uphoff
Harman Consumer International
FRANCE. 2/00
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