System information
X-Array Touring Loudspeaker Systems – Applications Notes – Page 9
When multiple systems are arrayed, the lower frequencies tend to build up due to mutual coupling and
increased directivity, resulting in the SUB and LF acoustic output being higher than that of the MB and
HF sections. The difference will depend on the number of subwoofer and bass boxes compared to the
number of mid/high boxes, the acoustic coupling of multiple subwoofer and bass boxes, and the acoustic
coupling of the subwoofer and bass boxes with the room (for example, flying versus ground stacking).
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 levels.
HELPFUL HINT: When tuning an X-Array system, the user should adjust the output levels to compen-
sate for efficiency differences between the frequency bands due to array coupling, room coupling and
room buildup. This usually requires adjusting the subwoofer and/or low-frequency output levels relative to
the mid-bass- and high-frequency output levels. The user is cautioned that substantial adjustments in
output levels and equalization could possibly lead to a gain-structure problem within the digital controller.
If, after the system has been tuned, the input is clipping and the output levels are low (as indicated by the
LEDs), the output level of each section of the digital should be increased. If, on the other hand, the input
level is low with the output levels are high (resulting in output clipping or excessive hiss and noise from
the crossover), the output level of each section should be decreased.
Optimizing the Gain Structure
For the best signal-to-noise ratio, the analog and digital gain structure of the digital controllers should be
adjusted for maximum performance. In general, this means adjusting levels so that all input analog-to-
digital (A/D) converters and output digital-to-analog (D/A) converters are operating at levels high enough
to utilize their full dynamic range. Most controllers feature provisions for manually programming the ana-
log output gain/attenuation stages, allowing the user to tailor the gain structure to make use of the full
dynamic range of the converters.
To maximize the signal-to-noise ratio, the user must first make sure that the input-signal level is high
enough to use the full dynamic range of the A/D converter. This is typically best achieved by having the
controller analog input gains set so that instantaneous program peaks are –5 to –10 dB below clipping at
the input A/D converter. Furthermore, the signal-to-noise ratio is maximized when output peaks are also
–5 to –10 dB below clipping at the output D/A converters. Without attenuation, this output drive level
would result in severe amplifier clipping. Thus, the output level must be attenuated in the analog domain
(post D/A). This is typically done from within the digital controller (although the same could be achieved
by turning down the power amplifier input-level knobs).
Caution must be exercised when setting up the gain structure within the digital controller to prevent in-
process clipping on instantaneous peaks that can degrade the sound quality or cause loudspeaker fail-
ure. The sharp corners of the square waves that occur when instantaneous program peaks are clipped
can result in excessive acceleration and deceleration forces that are mechanically harmful to a loud-
speaker – particularly HF compression drivers.
By their nature, HF compression drivers are fragile and are less tolerant of abuse than cone-type loud-
speakers. Thus, special care must be taken to prevent any in-process clipping in the HF audio path
throughout the controller. Repeated occasional clipping can reduce the life of the HF compression driv-
ers.
The 12-inch MB drivers are more tolerant of abuse than the HF drivers and, as such, repeated occa-
sional clipping will not typically reduce the life of the MB drivers. However, special care must also be
taken to prevent clipping in the MB signal path because it is usually audibly objectionable because the
MB section reproduces much of the vocal range.
The LF and SUB drivers in the X-Array™ systems are reasonably tolerant of abuse. Furthermore, the
acoustic design of the X-Array™ LF and SUB systems is such that the harmonic distortion that results