8
SETTING UP THE GTi AMPLIFIER
SETTING THE CROSSOVER
IMPORTANT: If you plan to use the
A3000GTi to drive full-range speakers,
set the crossover mode switch to FLAT
and skip to the next section, “Setting
Input Sensitivity.”
1. Depending on your system plan,
set the A3000GTi’s crossover mode
switch to LP (low-pass) or HP (high-
pass). The A6000GTi is a low-pass
amplifier only, designed to drive
subwoofers. No crossover switch
is provided.
2. The crossover slope has two
settings: 12 (dB per octave) or
24 (dB per octave). Select the
slope that best suits your taste, but
consider that a steeper low-pass
filter will make the subwoofers
sound less directional (since more
midrange will be filtered from the
signal). A steeper high-pass filter
will reduce a small speaker’s
unnecessary cone excursion at
the lowest frequencies, which
will increase power handling
and reduce distortion.
3. Set the A3000GTi’s HP FREQ control
to allow the speakers to make
as much bass as possible while
minimizing distortion caused by
small speakers trying to reproduce
the lowest frequencies. The best
setting is one where the speakers
produce crisp, clear impact without
being overdriven.
4. For either amplifier, set the LP FREQ
control so vocal information is not
reproduced by the subwoofers, and
the subwoofers’ sound blends with
the sound of the midrange speakers
without any missing information.
NOTE: The LP FREQ control can be
set to any frequency between 32Hz
and 320Hz.
SETTING INPUT
SENSITIVITY
NOTE: You can use the supplied
REMOTE LEVEL control to fine-tune
the input sensitivity or to adjust the
level of the bass according to the
program material after the amplifier’s
LEVEL control has been set properly.
Connect the remote module’s attached
cable to the REMOTE LEVEL (RJ45) jack
on the amplifier’s input panel. Start
with the REMOTE LEVEL Control in its
maximum (clockwise) position.
1. Initially, turn the amplifier’s LEVEL
control to the minimum (clockwise)
position.
2. Reconnect the (–) negative lead to
your vehicle’s battery. Apply power
to the audio system and play a
favorite music track.
3. Increase the source unit’s volume
control to the maximum listening
position. Slowly turn the amplifier’s
LEVEL control counterclockwise and
observe the I/OPT and E/OPT LEDs
(on the amplifier’s top).
• In the bridged or 2-channel mode,
at the ideal setting, the E/OPT LED
should flash on musical peaks to
indicate the amplifier is producing
maximum voltage. If the I/OPT LED
flashes in bridged mode, this
indicates the speaker system’s
impedance is lower than 2 ohms
and the amplifier should be
configured in the parallel mode.
• In the parallel mode, at the ideal
setting, the I/OPT LED should
flash on musical peaks to indicate
that the amplifier is producing
maximum current.
If either the I/OPT or E/OPT LED is
on steadily, the amplifier is being
overdriven and your speakers may
be in jeopardy. Turn the LEVEL
control back slightly until the I/OPT or
E/OPT LED flashes on musical peaks.
SETTING PHASE
1. Initially set the PHASE control to 0.°
Play a favorite audio track that has
significant bass output.
2. Continue listening to the music and
have another person slowly adjust
the PHASE control towards 180° and
back to 0° again.
3. Repeat Step 2 as needed until you
find a setting that produces the
most mid-bass output.
NOTE: For applications using multiple
GTi amplifiers where the highest SPL
is desired at a single point in the
vehicle (i.e., SPL competition), adjust
the PHASE controls on all amplifiers
so all speakers are in phase at the
microphone position. This will provide
the highest SPL when measured with
an SPL meter.
SETTING DBO
DBO (or Dynamic Bass Optimizer) is
a 12dB/octave high-pass filter with
variable frequency (20Hz to 80Hz)
and variable boost (0 to +12dB) at
the cutoff frequency.
NOTE: During DBO adjustment, you can
audition the effect by setting the DBO
switch to OFF and then back to ON.
NOTE: The A3000GTi can be used
to drive a pair of stereo mid-bass
speakers. In this case, use the DBO
to set the high-pass filter (from 20Hz to
80Hz) and use the crossover to set the
low-pass filter (from 80Hz to 320Hz).
For a
vented box
where a subwoofer
is prone to overexcursion below the
tuned frequency, set DBO to ON and
set the DBO HP FREQ control 10Hz
below the box’s resonant (tuned)
frequency (e.g., 30Hz for a vented
box tuned to 40Hz). Power typically
wasted in this region will now be
conserved and instead be available
for frequencies the enclosure can
reproduce. Use the DBO BOOST
control to boost the bass at the set
frequency by as much as 12dB, as
shown in Figure 13.
For a
sealed enclosure
, use DBO to
enhance the middle of the bass region.
Set DBO to ON, and then set the DBO
HP FREQ control to 35Hz to 40Hz.
Adjust the DBO BOOST control for a
big and full bass sound. Alternatively,
for a tighter-sounding bass, set the
DBO HP FREQ control between 45Hz to
50Hz and also adjust the DBO BOOST
control according to your preference.
For an
infinite baffle
application,
set DBO to ON, and then set the
HP FREQ control to the speaker’s Fs
value (to keep the subwoofer from
trying to create bass below the
resonant frequency). Adjust the DBO
BOOST control according to your taste.
–9
–6
–3
0
–12
20
80
Freq. (Hz)
dB
DBO HP FREQ Control
(adjusts cut-off
frequency)
–6
0
6
12
–12
20
80
Freq. (Hz)
dB
DBO BOOST Control
(adjusts boost amount
at cut-off frequency)
HP FREQ
20Hz
80Hz
BOOST
MAX
MIN
Figure 13.
Frequency response curves
show typical DBO control ranges for
the JBL A6000GTi or A3000GTi amplifier.
