JL Audio HD900/5 - Manual (Page 11)

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while the “Sub” channel filter is a low-pass filter
(attenuates high frequencies). For each filter, the
user can select from a shallow (12dB/octave) filter
slope or a more aggressive (24dB/octave) slope.
1) “High-Pass Filter” Controls (Front and Rear
channels) or “Low-Pass Filter” Control (Sub
Channel): These switches allow you to select filter
slopes or defeat the filter(s) completely.
“Off”: Defeats the filter completely. Useful when
using an external crossover, such as one built into
a head unit or signal processor.
“12dB”: Configures the filter to attenuate
frequencies above or below the selected
filter frequency at a rate of 12 dB per octave
(Butterworth alignment).
“24dB”: Configures the filter to attenuate
frequencies above or below the selected filter
frequency at a rate of 24 dB per octave (Linkwitz-
Riley alignment).
Depending on the speaker system and the
vehicle, different filter slopes may be required to
produce a smooth transition between the sound
of different speakers in the system.
In high-pass mode, the sharper “24dB” setting
will do a better job of protecting small speakers
with limited power handling. In low-pass
mode, the “24dB” setting can also help by more
aggressively removing lower midrange output
from a subwoofer system.
The shallower “12dB” octave setting
allows for more output overlap between
the speakers being crossed over. In many
cases, this will result in a smoother “blend”
or transition between speaker systems.
Experiment to find the slope or combination
of slopes which best matches the acoustic
requirements of your system.
2) “Filter Freq. (Hz)” Control:
This control selects the frequency at which the
filter begins to attenuate the signal and refers
specifically to the frequency at which output
has been attenuated by -3dB.
The filter frequency markings surrounding this
rotary control are for reference purposes and are
generally accurate to within 1/3 octave or better. If
you would like to select the filter cutoff frequency
with a higher level of precision, consult the charts
in Appendix B (page 18) of this manual.
“80 Hz” is a good starting point for most systems
where a subwoofer is connected to the Subwoofer
Channel and component systems or coaxials to
the four main channels.
inFrasonic Filter (subwoofer ch. only)
The “Infrasonic Filter” is a 24 dB/octave high-
pass filter, with a fixed cutoff frequency of 30 Hz.
This filter is designed to conserve amplifier power
and protect subwoofer systems, without audibly
degrading the sub-bass output.
With ported enclosures, the use of the
“Infrasonic Filter” is highly recommended to
protect the speaker(s) from excessive excursion
below box tuning.
With sealed enclosures, the use of the filter
is less necessary, but can still help protect the
speaker system from excessive excursion.
The “Infrasonic Filter” can be completely
defeated by selecting the “Off” position on its
switch. This bypasses all signal from flowing
through the circuit.