System information

X-Array Touring Loudspeaker Systems – Applications Notes – Page 13
capability with reasonable degree of loudspeaker protection. The digital-limiter thresholds may be ad-
justed lower, but should not be increased because of the increased risk of loudspeaker failure. If amplifi-
ers other than the Electro-Voice P3000 are used (other Electro-Voice P-series amplifiers or amplifiers
from other manufacturers), the limiter thresholds must be calibrated for those amplifiers as described
below. Furthermore, if the digital controller has the analog output level adjusted to a gain other than 0
dB, the limiter threshold must also be recalibrated.
Whenever possible, the digital controller should be set up so 0 dB on the output-level display is refer-
enced to the limiter threshold (i.e., dB from limit). In this configuration, the 0-dB LED will light when the
limiter threshold in that frequency band has been exceeded and gain reduction has occurred, giving the
operator an accurate representation of the power levels being delivered to the loudspeakers. During loud
portions of program material, it would be typical to see these LEDs flashing. The limiter parameters in the
spreadsheets will allow a small amount of amplifier limiting and/or clipping on instantaneous peaks; how-
ever, the limit/clip indicators on the amplifiers may not turn on when the digital controller 0-dB LEDs turn
on, because the response time of the amplifier LEDs may not be fast enough.
HELPFUL HINT: When tuning an X-Array system, it is essential that the digital limiter thresholds be
calibrated to protect the loudspeakers. The limiter thresholds in the included digital-parameter spread-
sheets have been calibrated for the Electro-Voice P3000 power amplifiers and post-limiter output gain of
0 dB. If amplifiers other than the P3000 are used, the limiter thresholds must be recalibrated. Further-
more, if the digital controller has a post-limiter gain other than 0 dB, the limiter thresholds must be recali-
brated. The user may turn the limiter thresholds lower for additional driver protection, but should not turn
the thresholds higher because of the increased risk of loudspeaker failure. It would be typical to see the
0-dB LED flash during loud portions of the program material, indicating that threshold of the limiter has
been exceeded and gain reduction has occurred.
Calibrating the Digital-Controller Limiters
The limiter thresholds in the digital-parameter spreadsheet are calibrated for the Electro-Voice P3000
power amplifiers which have a gain of 42 dB. Those limiter thresholds have also been calibrated for 0 dB
of post-limiter gain (both analog and digital). If amplifiers with a gain other than 42 dB are used, or if the
post-limiter gain is not 0 dB, the digital limiter thresholds must be recalibrated to provide sufficient pro-
tection of the loudspeakers and to minimize amplifier clipping.
The digital limiter is used for two purposes. The first is to limit the maximum voltage allowable to reach
the loudspeakers; thus, protecting the loudspeakers from extremely high voltage peaks that could dam-
age the drivers. The second is to minimize amplifier clipping; thus protecting the loudspeakers from se-
vere square waves that could damage the drivers.
The digital limiter thresholds should be calibrated as follows.
1. Disconnect the loudspeakers from the power amplifiers. Connect outputs of the digital controller to
the power-amplifier inputs.
2. Set the post-limiter gains (either digital or analog) to the level at which the system will be operated.
3. Set the amplifier controls for maximum gain.
4. Disable the digital-controller limiters by adjusting the thresholds for their maximum value.
5. Connect a sine-wave oscillator to the input of the digital controller. Select the frequency indicated for
the specific frequency band from the chart below and connect an oscilloscope to the amplifier output.
6. For amplifiers that do not have internal compressor/limiters - Turn the oscillator output level up until
the amplifier just barely begins to clip. If the amplifier is clipping at a voltage that is greater than the
voltage shown in the table below, turn the controller-limiter threshold down so that the amplifier volt-
age is reduced to that shown in the table below. If the amplifier is clipping at a voltage less than that
indicated in the table below, adjust the controller-limiter threshold so that the clipping Is eliminated.
7. For amplifiers that do have internal compressor/limiters - Turn the oscillator output level up until the
amplifier limiter just barely turns on. If the amplifier is limiting at a voltage that is greater than the volt-