System information

X-Array Touring Loudspeaker Systems – Applications Notes – Page 24
HELPFUL HINT: When setting up an X-Array system, if the console and/or drive electronics are clipping
and the DN8000 input-level LEDs indicate a low input level, turn up the DN8000 input-level knob. The
input-level LEDs indicate dB from clipping.
Output-Level Adjustments
The DN8000 output-level controls (both the output-level knobs and the "Main" menu output-level set-
tings) are in the digital domain and are used to adjust for the relative efficiency differences between the
SUB, LF, MB and HF sections of the loudspeaker systems. The DN8000 output-level settings shown in
the included spreadsheets provide a nominally flat frequency response for a single system. As discussed
in the general-signal-processing section, the SUB and LF sections tend to couple and build up level more
than the MB and HF sections when multiple systems are arrayed. The balance may be restored by a
combination of turning down the SUB- and LF-output levels, and turning up the MB- and HF-output lev-
els. The output levels may be adjusted either by the output-level knobs or by the encoder from the "Main"
editing screen. Note from the digital-parameter spreadsheets that the starting point for the output-level
knobs is the maximum-clockwise (0-dB-gain) position. The output-level display on the front panel should
be referenced to dB from limit (in other words, full-scale 0 dB is the threshold that the limiter is activated
and gain reduction will occur). See the “Options Menu Parameters” section earlier in this appendix for
setting the output-display reference.
Optimizing the Gain Structure
For the best signal-to-noise ratio, the analog- and digital-gain structure of the DN8000 should be ad-
justed for maximum performance. As noted in the general-signal-processing section of these applications
notes, that means adjusting levels so that the analog-to-digital (A/D) converters and digital-to-analog
converters (D/A) are operating at levels high enough to utilize their full dynamic range.
The first step is to make sure that the input levels are high enough to use the full dynamic range of the
A/D converters. This can be done through a combination of adjusting the drive level of the mixsite (con-
sole or front-of-house/control-room outboard processors) or the input-level controls of the DN8000 until
the DN8000 input display shows instantaneous program peaks of –5 to –10 dB below clipping. (The 0-dB
LED on the input display corresponds to A/D-converter clipping.)
The next step is to make sure that the output levels are high enough to use the full dynamic range of the
D/A converters. Full output of the DN8000 D/A converters is +9.75 volts rms; however, most amplifiers
require only between 0.5 to 1.0 volts rms to be driven to full power – some 20 dB below the full-dynamic
range of the D/A converters. In a previous section of these applications notes, it was recommended that
the user choose from the “Options” menu the option for a 2.45-volt-rms-maximum-output level. This op-
tion inserts 12-dB analog pads at the each of the DN8000 outputs, resulting in the D/A converters being
driven 12 dB harder. Thus, in this configuration, typical amplifiers are driven to full power about 8 dB be-
low the full-dynamic range of the D/A converters, improving the dynamic range and the signal-to-noise
ratio.
With the DN8000 operated in the 2.45-volt-rms-maximum-output configuration, the user must avoid using
excessive digital gain or digital equalization boosts that could result in in-processing digital. The head-
room in the digital controller can be verified by temporarily changing the output display from the “Options”
menu to display “dB from Clip”. In the “dB from Clip” display mode the 0-dB red LED indicates clipping.
After verifying the digital headroom, the display should be returned from the “Options” menu to “dB from
Limit” for normal operation. In the “dB from Limit” display mode the 0-dB red LED indicates that the limi-
ter threshold has been exceeded and that the limiter is reducing gain to protect the loudspeakers. The
“dB from Limit” mode is preferred for normal operation because the user has a more accurate represen-
tation of how hard the loudspeakers are being driven.