8
| JL Audio - 250/1
v2
Owner’s Manual
9
2)
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.
3) Defeating the Amplifier Filter:
The Low-
Pass filter can also be defeated completely,
by switching the “
Mode/Slope
” switch to the
“
Off
” position. This is useful if you are using
an external active crossover in the system.
Keep in mind that turning the internal
crossover off also defeats the “
Bass Boost
”
processing (see next section for details). With
the internal crossover turned off, the 250/1v2’s
upper frequency response limit is 250 Hz, due
to its bass-specific Class D design.
bass Control seCtion
The 250/1v2 includes a basic bass processing
section consisting of two primary components:
a fixed-frequency, 24 dB/octave infrasonic filter
and a fixed-frequency/“
Q
”, single-band equalizer
centered at 48 Hz.
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 affecting
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)
“
LF (Low-frequency) Boost
”: This feature
allows the user to control the boost of a
fixed “
Q
”, fixed-frequency equalization
band centered at 48 Hz. The “
LF Boost
”
control knob determines how much boost
(in dB) you are adding to the bass signal.
A range of 0 - 15 dB of boost is available.
If no boost is desired, rotate the “
LF
Boost
” knob fully counterclockwise.
The
“Remote Bass Port”
allows the
connection of an optional remote boost knob
(the RBC-1) that can be mounted in the front of
the vehicle. This optional control takes the place
of the
“LF Boost”
knob on the amplifier when
connected and bypasses the
“LF Boost”
rotary
control on the amplifier.
IMPORTANT
!
The “LF Boost” and “Infrasonic Filter” features
will only operate when the subwoofer channel's
filter is activated with the “Sub LP Filter”
switch in the “12dB” or “24dB” position. These
features will not work with the “Sub LP Filter”
switch in the “Off” position. This is to prevent
cascading the processing of multiple amplifiers
when configured in a master / slave
arrangement. If you are using an external
active crossover and would like to use the “LF
Boost” and “Infrasonic Filter” features, set the
“Amp LP Filter” switch on “12dB” and rotate
the frequency selection knob fully clockwise to
the “200 Hz” position. This will activate the
bass processing features without significantly
affecting the crossover point selected by the
external active crossover.
3) Input Sensitivity Adjustment
: Located
next to the “
Input Voltage
” switch, in the
“
Amplifier Input Section
”, is a rotary control
labeled “
Input Sens.
”. Once the appropriate
“
Input Voltage
” range has been selected, this
rotary control can be used to match the source
unit’s output voltage to the input stage of the
amplifier 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 the amplifier
for maximum clean output, please refer to
Appendix A (page 12) in this manual. After
using this procedure, you can then adjust
the level of the amplifier by adjusting the
input sensitivity downward, if the amplifier
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 A (page
12). Doing so will result in audible distortion
and possible speaker damage.
CrossoVer Controls
Crossovers are groups of individual electronic
filters which allow only certain frequency
ranges to pass through them by attenuating
frequencies outside the selected range. These
filters allow the user to specify what frequency
range will be sent out of each channel section
of the amplifier. This, in turn, allows each
speaker system to only reproduce a range of
frequencies it is well-suited for, resulting in
reduced distortion and improved fidelity.
amPliFier low-Pass Filter
The 250/1v2 employs a sophisticated, state-
variable, low-pass active filter for its internal
channel. This feature is designed to attenuate
frequencies above its filter frequency, so that the
system’s subwoofers do not reproduce any audible
midrange content.
1)
Filter Operation:
The low-pass filter in the
250/1v2 is fully variable between 40 Hz and
200 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 “
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.
