408 GTi - JBL Car Audio User Guide / Operation Manual. Page 14

used and at or above 3.5kHz if you are
using an 18 or 24dB per octave crossover.
In this configuration, the crossovers
supplied with the 408 and 508GTi 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/midrange is
150 watts for the 408GTi and 200 watts for
the 508GTi. The maximum recommended
RMS amplifier power routed directly to the
tweeter is 125 watts.

The 408 and 508GTi Woofer/

Midranges use many high strength
materials which require a break-in period
before they will achieve top performance.
The drivers need to be broken in at a
medium volume level for about 1 hour
before maximum performance is achieved.

As a result of their high efficiency, all

JBL loudspeakers will produce reasonable
volume levels in the automotive environment
using very little amplifier power. However,
the use of a low-powered amplifier to attain
very high volume levels could lead to
overdriving the amplifier. This will generate
high distortion levels which can easily
damage loudspeakers, 

even if the rated

power of the amplifier is below the rated
maximum power handling of the
loudspeaker!

As a general rule, do not turn up the

volume control past the point where you
hear distortion in the form of either signal
distortion from an overdriven amplifier or
mechanical noise from an overstressed
speaker. 

For the best performance and

system reliability, you should select an
amplifier with an output rating greater than
the maximum power likely to be used to
generate the desired volume levels. If you
want your system “Loud + Clear,” we
suggest that you step up to a JBL power
amplifier which has an RMS power rating
equal to, but not exceeding, the 

Maximum

Recommended Amplifier Power listed in
the specifications of your specific JBL

speaker. This margin of reserve power will
ensure that the amplifier will not attempt to
deliver more power than its design allows.
Your dealer will be happy to point out
which high power JBL amplifiers are
optimum for your application and listening
habits.

Following these guidelines will provide

virtually distortion free sound reproduction
and long loudspeaker life.

The most common difficulties are

noise, distortion, and intermittent
connections.

System noise is usually not the fault

of the 408 and 508GTi. Hiss or “alternator
whine” is most often the result of faulty
grounding of the system electronics or
improper setting of amplifier level controls.
An exception to this is if the passive
crossover networks are mounted near a
source of radiated noise, the network may
pick up this noise with sufficient power to
drive the 408 and 508GTi. For this reason,
be careful not to mount any passive

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408/508 MANUAL.QXP  7/17/98 11:21 AM  Page 14