JBL 508GTI manual System Connections, Figure M

OdB	Tweeter Level Adjustment Switch
–2dB
–4dB

Figure M

System Connections

There are a variety of system options available with the 408 and 508GTi. The simplest configuration is to use the 408 and 508GTi full range. Although this will yield good sound, the best performance will be achieved in a high-end system which includes subwoofers and, optionally, midbass transducers. Because the 408 and 508GTi are specifically designed

for mid and high frequency operation, they should have their extremely low frequencies blocked by electrical means in order to achieve the best system fidelity and the widest dynamic range. Full range

use may be obtained at slightly lower power handling levels.

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 408 or 508GTi. 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 60Hz and 150Hz when using the 508GTi and between 80Hz and 150Hz when using the 408GTi. 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 woofer/midranges. 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 408 or 508GTi 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 woofer/midrange transition point and install it in-line ahead of the 408 or 508GTi 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- woofer/midrange transition point and at the woofer/midrange-to-tweeter transition. Set the high crossover frequency at or above 5kHz if a 12dB per octave crossover is

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