400 GTi - JBL Car Audio User Guide / Operation Manual. Page 8

that the 400 and 500GTi should always be
connected in the same polarity as the tweeter
however. It is possible, that due to the
difference in the distance the sound travels
from the woofer/midrange to your ears
compared to the distance from the tweeters in
a typical system, and the short wavelengths of
sound at the crossover frequency, that a
connection where the tweeters are connected
in reverse polarity from the other drivers in the
system may actually result in better sound.
Because there is no way to accurately predict
this before installation, we recommend that
you try the connection both ways, and leave it
in the polarity that gives the smoothest audible
transition between the woofer/midrange and
tweeter.

There are a variety of system options

available with the 400 and 500GTi. The
simplest configuration is to use the 400 and
500GTi connected in parallel to a tweeter
which includes a high-pass crossover such as
the 08GTi, GT03 or GT07. Because the 400
and 500GTi is specifically designed for mid

frequency operation, it should have its high
and extremely low frequencies blocked by
electrical means in order to achieve the best
system fidelity and the widest dynamic range.

For the best performance, we recom-

mend that an active crossover with a
minimum of 12dB per octave slope be used
for the transition point between the subwoofer
and the 400 or 500GTi. The optimum
crossover frequency for this transition is de-
pendent on the specific components used, the
vehicle, and other installation details. As a
general rule, the crossover frequency should
be as low as possible to achieve the best sys-
tem imaging. You can fine-tune the crossover
after the installation is complete for the best
sound. A good place to start your tuning
process is between 50Hz and 150Hz when
using the 500GTi and between 80Hz and
150Hz when using the 400GTi. In 4-way sys-
tems using a midbass driver such as the
600GTi, the crossover point may be raised
higher without detrimentally affecting imaging
as long as the midbass drivers can be 
mounted reasonably close to the midranges.
This higher crossover fre-quency will allow the
system to play louder. Since no crossover is

perfect, it is advisable to keep your crossover
points away from the range where your 
hearing is most sensitive. Therefore we 
recommend that you try to keep the high-pass
frequency below 250Hz and the low-pass
above 2500Hz. This lets the 400 or 500GTi
reproduce the entire range of frequencies,
covering the most important vocal and 
lead instrument fundamentals without a
crossover point.

If you prefer to use all passive

crossovers, you will need to construct or
purchase either a low-pass or band-pass 
filter for the midrange driver and match it 
to a high-pass filter for the tweeter. When a
matched GTi Competition Series system 
is used, the best crossover choice is the 
laboratory-optimized, system-matched
crossover which is included with the 408GTi or
508GTi system. If you have not yet installed
your components, we suggest that you 
consult your dealer for this system package.

The most advanced system designs

use active electronic crossovers such as
the JBL GTX2, GTX4 or GTX47 at both the
subwoofer(or midbass) to woofer/midrange
transition point and at the woofer/midrange

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400/600 MANUAL.QXP  7/17/98 11:10 AM  Page 8