For the best performance, we
recommend that an active crossover with
a minimum of 12dB per octave slope be
used for the transition point between the
Subwoofer and the 404 or 504GTi. The
optimum crossover frequency for this
transition is dependent 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 system
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 504GTi and
between 80Hz and 150Hz when using the
404GTi. In 4-way systems using a midbass
driver such as the 600GTi, the crossover
point may be raised higher without
detrimentally affecting imaging as long as
the woofer/midbass drivers can be
mounted reasonably close to the Coupled
Components
TM
. This higher crossover
frequency 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. This lets the 404
or 504GTi reproduce the entire range of
frequencies covering the most important
vocal and lead instrument fundamentals
and their harmonics.
If you prefer to use all passive
crossovers, you will need to construct
or purchase a high-pass filter for the
subwoofer to Coupled Component
TM
transition point and install it in-line ahead
of the 404 or 504GTi Crossover. For
the best system dynamic range, we
recommend that a minimum slope of 12dB
per octave be used.
The most advanced system designs
use active electronic crossovers such as
the JBL GTX2, GTX4 or GTX47 at both the
subwoofer (or woofer/midbass)-to-Coupled
Component
™
transition point and at the
woofer/midrange-to-tweeter transition. This
is possible with the coupled component
system because the tweeter and
woofer/midrange are accessible separately
through the individual sets of terminals.
Set the high crossover frequency at or
above 5kHz if a 12dB per octave
crossover is used and at or above 4.5kHz
if you are using an 18 or 24dB per octave
crossover. In this configuration, the
crossovers supplied with the 404 and
504GTi are not used. For tweeter
protection, a 1.5A fast acting fuse should
be installed in series with the tweeter.
The maximum recommended RMS
amplifier power routed directly to the
woofer/midbass driver is 125 watts for the
404GTi and 150 watts for the 504GTi.
When used with the appropriate crossover
and fused as recommended above, the
tweeter can be connected to amplifier
channels of the same power rating
although there is little point in using an
amplifier in excess of 50 watts when
driving the tweeter alone.
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