Crossover Controls; Infrasonic Filter - JL Audio HD750/1 Owner's Manual

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.
"input sens." Control
Located to the left of the "Input Voltage"
switch is a rotary control labeled "Input Sens.".
Once the appropriate "Input Voltage" range has
been selected, this control can be 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
Status
for a given input voltage). To properly set the
amplifier for maximum clean output, please refer
to Appendix C (pages 18, 19) in this manual.
80 120
60 200
12dB | 24dB Low | High
50 500
Filter Input Input
Slope Filter Freq. (Hz) Sens. Voltage
HD750/1 Monoblock Amplifier
After using this procedure, you can then adjust
the relative level by adjusting the input sensitivity
downward, if it requires attenuation to achieve
the desired system balance.
Do not increase the "Input Sens." setting for
any amplifier 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.
10 | JL Audio - HD750/1 Owner's Manual

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 HD750/1 has one filter, which can be
configured as a high-pass filter (attenuates low
frequencies) or as a low-pass filter (attenuates
high frequencies). Additionally, the user can
select from a shallow (12dB/octave) filter slope
or a more aggressive (24dB/octave) slope.
Status
80
60
O | HP | LP 12dB | 24dB
50
Filter Filter
Mode Slope Filter Freq. (Hz)
HD750/1 Monoblock Amplifier
1) "Filter Mode" Control: this switch allows you
to defeat or configure the filter into one of two
filter types:
0 | 180 deg. O | 30Hz
"Off": Defeats the filter completely, allowing
Output Infrasonic
Polarity Filter
the full range of frequencies present at the
inputs to feed the amplifier. This is useful
for systems utilizing outboard crossovers or
requiring full-range reproduction.
"HP" (High-Pass): Configures the filter
to attenuate frequencies below the selected
filter frequency. Useful for connection of
component speakers in a bi-amplified system.
"LP" (Low-Pass): Attenuates frequencies
above the selected filter frequency.
Useful for connection of subwoofer(s)
in a bi-amplified system.
2) "Filter Slope" Control: This switch allows you
to select from two filter slopes:
"12dB": Configures the filter to attenuate
frequencies above or below the selected
filter frequency at a rate of 12 dB per octave
(Butterworth alignment).
60
"24dB": Configures the filter to attenuate
O | HP | LP 12dB | 24dB
frequencies above or below the selected
Filter Filter
Mode Slope
filter frequency at a rate of 24 dB per octave
(Linkwitz-Riley alignment).
Depending on the speaker system and the
120
vehicle, different filter slopes may be required to
200
produce a smooth transition between the sound
Low | High 0 | 180 deg.
500
of different speakers in the system.
Input Input Output
Sens. Voltage Polarity
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.
3) "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.

inFrasoniC Filter

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.
80 120
200
Low | High 0 | 180 deg.
50 500
Input Input Output
Filter Freq. (Hz) Sens. Voltage Polarity
HD750/1 Monoblock Amplifier
With ported enclosures, the use of the
O | 30Hz
"Infrasonic Filter" is highly recommended to
Infrasonic
Filter
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.
O | 30Hz
Infrasonic
Filter
11