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Welcome to Club GTi .........................................................................3
About this Manual ..............................................................................3
Autosound at its Best .........................................................................3
Designing Your System ......................................................................4
Component Placement.......................................................................5
Installation Warnings and Tips ...........................................................5
Mounting Instructions .........................................................................6
Installing the GTi System Crossover ..................................................6
Woofer/Midrange Driver Mounting .....................................................7
Mounting the 408 and 508GTi Tweeter ..............................................8
Tweeter Surface Mounting Instructions ..............................................8
Tweeter Surface Angle Mounting Instructions ....................................9
Tweeter Flush Mounting Instructions ...............................................10
Tweeter Flush Angle Mounting Instructions......................................11
Wiring ...............................................................................................12
Crossover Tweeter Level Adjustment...............................................12
System Connections ........................................................................13
Speaker Break-In .............................................................................14
A Note on Power Handling ...............................................................14
In Case of Difficulty ..........................................................................14
Specifications ...................................................................................16
Thiele-Small Specifications ..............................................................17
Mounting Templates .........................................................................19

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Thank you for purchasing the finest

Automotive Component Systems JBL has
ever produced. As a GTi Competition
Series owner, you are a member of a
select group of people who enjoy the most
advanced mobile audio products available.
We call this group “Club GTi.” By sending
in the customer information card, which
you will find attached to your warranty, we
will automatically register you as a Club
GTi member which will give you access to
exclusive Club GTi apparel and other
special offers we will make available from
time to time. We suggest you fill the card
out at your earliest convenience.

Also, be sure to save your sales

receipt in a safe place. It will be necessary
to use this document as proof of purchase
in the event that you ever need warranty
service. It is also useful for insurance
purposes and for establishing value when
you re-sell your vehicle. 

Because of the performance capability

of your GTi Competition Series product,
and the variety of potential system
configurations, we strongly recommend
that you have the system professionally
installed. You will also get a better warranty
if your equipment is professionally installed
by an authorized GTi dealer and you have
your warranty card stamped. This manual
provides information on installation and
usage to help a skilled technician get the
most from your GTi Competition Series
product. This manual does not cover basic
information about installation which is
common knowledge to a professional
installer, except for information which is
unique to the 408 and 508GTi systems.

If you feel you possess the necessary

skills, and prefer to install the equipment
yourself, this manual will provide you with
the necessary specifics to properly use the
408 or 508GTi in typical installations.
Consult your JBL dealer, or a qualified
technician, for more information.

The 408 and 508GTi systems are built

to meet the same rigorous standards of
construction and performance that have
long established JBL’s renowned home
and professional speaker systems. The
408 and 508GTi Woofer/Midranges
incorporate advanced JBL woven Kevlar
cones which are especially suited to the
unique acoustic and environmental
conditions which characterize automotive
sound. The 408 and 508GTi Tweeter
incorporates advanced JBL pure titanium
technology which is especially suited to
the unique acoustic environment of
modern vehicles. The 408 and 508GTi
have been engineered to provide excellent
power handling, good dispersion and
balanced frequency response, along with
minimum size and flexible installation
options for optimizing placement within the
vehicle.

The small size of the GTi Drivers is

made possible through the use of a
Neodymium magnet assembly with JBL’s
Stray Field Containment Geometry. By

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minimizing stray magnetic fields, this
closed circuit magnetic assembly design
concentrates the magnetic field on the
voice coil where it provides superior
performance. In the woofer/midrange
drivers, this high concentration of magnetic
power is coupled to a 2" Edge-wound
Aluminum Wire Voice Coil on a High
Temperature Fiberglass Former. This voice
coil uses lightweight aluminum wire to
maintain the agility to reproduce high
frequencies while its large diameter and
fiberglass former assures extremely high
thermal power handling.

Treated Kevlar fiber cones are used

because of their combination of low 
weight, high stiffness and resistance to
resonances. The 408 and 508GTi
Woofer/Midranges are topped off with a
treated fabric inverted dome for smooth
reproduction of upper midrange
frequencies.

The cone motion of these high

excursion designs is controlled by a
Aromatic Polyamid Fiber Spider. This new
material is able to control the 0.6" motion 
of the cone while maintaining musical

accuracy because it is 3 times stronger
than conventional spider materials.

The tweeters in the 408 and 508GTi

feature domes made from pure titanium.
Pure titanium has long been known to have
a very high stiffness to weight ratio, making
it ideal for treble reproduction. However,
only JBL has “tamed” titanium through a
special manufacturing process. The dome
of the 408 and 508GTi Tweeter is created
using special nitrogen gas cooled forming
machines which can create a uniformly
paper-thin dome without the work-
hardening or deformation which causes
resonances in domes made without benefit
of this process

Equally important is the 408 and

508GTi crossover design. Each crossover
was meticulously optimized in JBL’s state-
of-the-art acoustic laboratory to guarantee
a seamless blend of the woofer/midrange
and tweeter output. Unlike generic or
general purpose crossovers, the design of
the 408 and 508GTi Crossovers was
performed with a full knowledge of the
performance characteristics of each driver,
allowing frequency, phase, and power

response to be completely optimized for
each combination.

What does all this technology add 

up to? A system with ideal frequency
response, excellent off axis response, 
and high output capability all in a small 
and elegant package. The result is
exceptionally smooth and detailed music
reproduction over the full range of
frequencies and clean sound that cuts
through road noise.

The overall quality of any system

design is a result of how well all of the
components work together, not just the
result of the performance of any one
component. JBL GTi Series woofer/
midbass or subwoofer transducers are 
the ideal companion products to your 408
and 508GTi systems. Each of the GTi
Competition Series products are designed
to complement the others to provide the
highest performance with the simplest and
most predictable system design. To use the
408 and 508GTi as the woofer/midrange

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and high frequency transducers in a high
quality system, we recommend you use
either a high quality active crossover 
such as JBL’s GTX47, GTX4 or GTX2 
to provide optimum matching to your
subwoofer or woofer/midbass loudspeaker.
If you prefer passive crossovers, we
recommend that you use only high quality
audiophile grade film-type capacitors 
and Low DCR inductors to get the most 
out of your system. The most popular
system configuration is a hybrid using 
an active crossover for the subwoofer to
woofer/midrange crossover point, and a
passive crossover for the woofer/midrange
to tweeter crossover. Your GTi Competition
Series Dealer is uniquely qualified to help
guide you on the best system configuration
for your needs.

The location of each of the

loudspeakers plays a vital role in achieving
proper frequency response and spacious
imaging. Because the 408 and 508GTi
systems have an extremely wide and

smooth dispersion pattern, excellent
performance may be achieved in any
vehicle. Due to the wide variety of vehicles,
there is not one “right” way to locate the
408 and 508GTi, however knowledge of
the following considerations will help you
get the most from your system:
1.

The most spacious stereo image is
achieved when the speakers are placed
as wide apart as possible.

2.

The best center image will be achieved
when the distance from the left speaker
to your left ear is as equal as possible to
the distance from the right speaker to
your right ear. This is most easily
achieved by placing the 408 or 
508GTi as far forward as you can.

3.

The best system integration is achieved
when the woofer/midrange is mounted
close to the tweeter. Installing the
tweeter close to the woofer/midrange
helps smooth the transition from
woofer/midrange to tweeter at the
crossover point.

4.

You will get the best frequency
response when the path from the
speakers to your ear is unobstructed.

5.

Because of the high acoustic energy
capability of the 408 and 508GTi, the
woofer/midrange drivers must be
securely mounted in a rigid panel which
is free from resonances, rattles and air
leakage.

•

Be careful not to cut or drill into fuel
tanks, fuel lines, brake or hydraulic
lines, vacuum lines or electrical wiring
when working on your vehicle. Inspect
behind panels before you cut or drill.

•

Be sure to check for clearance of
window, cranks and linkages when
mounting speakers in door panels.

•

Do not use the speakers unmounted.
Failure to securely mount this product
could result in damage or injury,
particularly in the event of an accident.

•

Although the materials used on the 408
and 508GTi are inherently water
resistant, do not mount the speakers
where they will get wet.

•

Always disconnect the ground wire
from the battery before doing any work
on the vehicle.

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