PREAMP OUTPUT SECTION
The 450/4 incorporates a pass-through preamp
output section, so that additional amplifiers can be
added to the system.This pass-through pre-amp
output can be configured three different ways
using the switch labeled
“Signal From”
in the
“Preamp Output Section”
.
1) “1&2”:
The preamp output delivers the
same signal that is connected to the 450/4's
CH 1&2 Inputs. This mode is useful for feeding a
subwoofer amplifier when the 450/4 is being used
to drive front and rear speaker systems.This
preamp output mode will track the signal level of
CH 1&2, allowing fading of the rear channels
without affecting the subwoofer level.
2) “3&4”:
The preamp output delivers the same
signal that is connected to the 450/4's CH 3&4
Inputs. This mode is useful for feeding a subwoofer
amplifier when the 450/4 is being used to drive
front and rear speaker systems.This preamp output
mode will track the signal level of CH 3&4, allowing
fading of the front channels without affecting the
subwoofer level.
3) “ALL”:
This mode delivers a sum of the signals
being fed to the
“CH 1&2 Input Section”
and
“CH 3&4 Input Section”
of the amplifier.This signal is
not affected by the
“LF Boost”
or
“Infrasonic Filter”
processing selected for the amplifier or by any
crossover filter selected (if the input signal is full-
range, the preamp output will be full-range).When
the 450/4 is being used to drive front and rear
speaker systems, this preamp output mode will
deliver a summed front/rear signal to the subwoofer
amplifier, while permitting fading of the front and rear
speaker systems from the source unit.
NOTE:
The signal level of the
“Preamp Output”
is
affected by the setting of the
“Input Voltage Range”
switches (of the input section(s) chosen by the
“Signal From”
switch). See the
“Input Voltage
Range”
section (page 6) for details on
“Input
Voltage”
settings.The preamp output level is not
affected by the “Input Sens.” rotary controls.
CH 1 & 2 BASS CONTROL
This section provides two basic bass processing
tools for CH 1&2: a 24 dB/octave infrasonic filter at
30 Hz and a +6 dB boost circuit centered at 48 Hz.
Activation of either feature automatically
sums the CH 1&2 input signals to mono.
(These features should only be used when
driving subwoofer(s) from CH 1&2).
1) “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. 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.The infrasonic filter can be completely
defeated by selecting the
“Off”
position on the
“Infrasonic Filter”
switch.This bypasses all signal
from flowing through the circuit.
2) Bass EQ:
This switch allows the user to
activate a 6 dB boost centered at 48 Hz.
3) Remote Bass Port:
Allows you to connect an
optional remote boost knob (sold separately,
JL Audio Model RBC-1) that can be mounted in the
front of the vehicle. With the RBC-1 connected, the
boost is no longer limited to 0 or +6 dB, allowing a
range of 0-15 dB of boost to be selected.
The
“Bass EQ”
and
“Infrasonic Filter”
features
will only operate when the CH 1&2 filter is
activated and in low-pass mode. If you are using an
external active crossover and would like to use the
“Bass EQ”
and
“Infrasonic Filter”
features, set the
I M P O RTA N T
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JL AUDIO
450/4
9
“24dB”:
Configures the filter for CH 1&2 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. Experiment to find
the slope which best matches the acoustic
requirements of the system.The sharper
“24dB”
setting will do a better job of protecting small
speakers with limited power handling.The shallower
“12dB”
octave setting allows the rear speakers to
reproduce more low-frequency content.
3) “Freq. Range” Control:
When thrown to
the right, this switch multiplies the cutoff
frequency selected by the rotary
“Filter Freq.
(Hz)”
control by a factor of 10. In the
“x1”
position, the range of the rotary control is
50 - 500 Hz (as marked). In the
“x10”
position, the range of the rotary control is
500 Hz - 5 kHz (5000 Hz).
4) “Filter Freq. (Hz)”
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 A
(page 20) of this manual.
CH 3&4 Filter Section:
1) “High-Pass Filter” Control:
This switch allows
you to defeat the CH 3&4 filter or select from two
different filter slopes.
“Off”:
Defeats the filter for CH 3&4 completely,
allowing the full range of frequencies present at the
inputs to feed that pair of channels.This is useful for
systems utilizing outboard crossovers or requiring
full-range reproduction from these channels.
“12dB”:
Configures the high-pass filter for CH 3&4
to attenuate frequencies below the selected filter
frequency at a rate of 12 dB per octave
(Butterworth alignment).
“24dB”:
Configures the high-pass filter for CH 3&4
to attenuate frequencies 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 speakers
in the system. Experiment to find the slope which
best matches the acoustic requirements of your
system.The sharper
“24dB”
setting will do a better
job of protecting small speakers with limited power
handling.The shallower
“12dB”
octave setting
allows the rear speakers to reproduce more low-
frequency content.
2) “Freq. Range” Control:
When thrown to the
right, this switch multiplies the cutoff frequency
selected by the rotary
“Filter Freq. (Hz)”
control by
a factor of 10. In the
“x1”
position, the range of the
rotary control is 50 - 500 Hz (as marked). In the
“x10”
position, the range of the rotary control is
500 Hz - 5 kHz (5000 Hz).
3) “Filter Freq. (Hz)”
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 A
(page 20) of this manual.
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JL AUDIO
450/4
