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| JL Audio - MHD900/5 Owner’s Manual
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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
vessel, 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.
The output of the amplifier decreases for a
given input voltage when the “Input Range”
switch is placed in the “High” position. The
output increases with the switch in the “Low”
position. While this may sound counter-
intuitive, it is correct as described.
CHannel Control seCtions
To the left of the
“General Setup”
section on
the Control Panel of the amplifer are three sets of
controls: one for the
“Rear Channel Controls”
one for the
“Front Channel Controls”
and
one for the
“Subwoofer Channel Controls”.
In each of these sections you will find a
rotary control labeled
“Input Sens.”
(Input
Sensitivity). These controls are designed to match
the input sensitivity of each channel section of
the MHD900/5 to the specific signal source that
is feeding the amplifier. These controls must be
adjusted, with care, following the procedures
outlined in this manual. Failure to make correct
adjustments can result in weak output, excessive
distortion and/or undesirable noise in the audio
output of the amplifier!
Note:
The Channel Control sections also house
“High-Filter” or “Low-Pass Filter”
and
“Filter
Freq.”
controls. These are crossover filter controls
and will be discussed in the next section of this
manual. This section will explain the Input
Controls only.
“input sens.” Controls
Once the appropriate
“Input Voltage”
range
has been selected in the “General Setup” section
of the amplifier, the “Input Sens.” controls are
used to match the source unit’s output voltage to
the input stage of each pair of amplifier channels
for maximum clean output. Rotating the control
clockwise will result in higher sensitivity (louder
for a given input voltage). Rotating the control
counter-clockwise will result in lower sensitivity
(quieter for a given input voltage). To properly
set each pair of amplifier channels for maximum
clean output, please refer to Appendix C (pages
18, 19) in this manual.
After using this procedure, you can then adjust
the relative level of each channel pair by adjusting
the input sensitivity downward on any of the
channel sections, if they require attenuation to
achieve the desired system balance.
Do not increase the
“Input Sens.”
setting for
any amplifier or channel section in the system
beyond the maximum level established during
the procedure outlined in Appendix C (pages 18,
19). Doing so will result in audible distortion and
possible speaker damage.
Be aware that all three
“Input Sens.”
adjustments will need to be made, regardless
of how many input cables are feeding the
amplifier. These controls will allow you to set
the appropriate relative levels for the
“Front”
channels relative to the
“Rear”
channels and the
“Sub”
channel (and any other amplifier channels
in the system).
CrossoVer Controls
Crossovers are groups of electronic filters
designed to control the frequency ranges
that each speaker in a system will be tasked
with reproducing. Proper crossover setup is
critical to sound quality and reliability.
The MHD900/5 has three individually
adjustable filter controls, one for the
“Front”
channels, one for the
“Rear”
channels and
another for the
“Sub”
channel. The “Front”
and “Rear” filters are high-pass filters (they
attenuate low frequencies), while the
“Sub”
