Setting UP the GTI Amplifier, Setting Phase

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 maxi- mum (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 max- imum 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 pro- vide the highest SPL when measured with an SPL meter.

DBO HP FREQ Control

HP FREQ

(adjusts cut-off

frequency)

80Hz

20Hz

–3

–6

–9

–12

Freq. (Hz)

DBO BOOST Control

BOOST

(adjusts boost amount

at cut-off frequency)

MIN

MAX

–6

–12

Freq. (Hz)

Figure 13. Frequency response curves show typical DBO control ranges for the JBL A6000GTi or A3000GTi amplifier.

SETTING DBO

DBO (or Dynamic Bass Optimizer) is

a 12dB/octave high-pass filter with vari- able 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.