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8 | JL Audio - XD600/1 Owner’s Manual
FILTER CONTROLS
Most speakers are not designed to reproduce
the full range of frequencies audible by the human
ear. For this reason, most speaker systems are
comprised of multiple speakers, each dedicated
to reproducing a specific frequency range. Filters
are used to select which frequency range is sent
to each section of a speaker system. The division
of frequency ranges to different speakers can be
done with passive filters (coils and/or capacitors
between the amplifier outputs and the speakers),
which are acceptable and commonly used
for filtering between mid-range speakers and
tweeters. Filtering between subwoofer systems
and satellite speaker systems is best done with
active filters, which cut off frequency content at
the input to the amplifier. Active filters are more
stable than passive filters and do not introduce
extraneous resistance, which can degrade
subwoofer performance.
The active low-pass filter built into
the XD600/1 is designed to attenuate
frequencies above its filter frequency,
so that the system’s subwoofers do not
reproduce any audible midrange content.
This serves to improve tonal balance
and to avoid distortion. Correct use
of the filter can substantially improve
the fidelity of your audio system.
2) LP Filter Operation: The low-pass filter in the
XD600/1 is fully variable between 50 Hz and
500 Hz via the “Filter Freq.” control knob and
features the ability to select between a moderate
“12dB” per octave or a steep “24dB” per octave
slope via the “LP Filter Mode/Slope” switch.
Depending on the subwoofer system and
the vehicle, different slopes may be required
to produce a smooth transition to the mid-
bass speakers in the system. Experiment to
find the slope which best matches the acoustic
requirements of your system.
Tuning Hint: A trunk mounted sub whose
output has to “fight” through a rear deck or a
back seat often benefits from the 12 dB/octave
slope which lets more upper bass content pass
through. A sub that fires directly into the
listening environment is more likely to benefit
from a 24 dB/octave slope.
Note: The above hint is not “set-in-stone”…
You should always listen to the system carefully to
determine the best choice as vehicle acoustics and
other factors play a big role in choosing the most
appropriate filter slope.
3) Precise Frequency Selection: The filter
frequency markings on the front panel of
the amplifier are for reference purposes and
are generally accurate to within 1/3 octave
or better. If you would like to select the filter
frequency with a higher level of precision,
consult Appendix B (page 13) of this manual.
This chart gives you a more accurate frequency
for each of the forty detented positions of the
frequency selection control. This method can
be very useful if the amplifier is mounted in
a location where you can’t see the front panel
markings easily.
4) Defeating the LP Filter: The Low-Pass filter
can also be defeated completely, by switching
the “LP Filter Mode/Slope” switch to the
“Off” position. This is useful if you are using
an external active crossover in the system.
With the internal crossover turned off, the
XD600/1’s upper frequency response limit is
500 Hz, due to its subwoofer-specific design.