L-Acoustics V-DOSC, Руководство оператора

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L-ACOUSTICS V-DOSC Manual Version 4 6/29/2005 Page 58 of 158
GENERAL GUIDELINES REGARDING SYSTEM PROTECTION
As supplied by L-ACOUSTICS, limiter thresholds for all V-DOSC OEM factory presets are initially set
at +9, +8, +9 and +9 dBu for sub, low, mid and high sections, respectively. These limiter thresholds
are matched to the input sensitivity of the L-ACOUSTICS LA48a (+9.5 dBu) and the recommended
power handling for each section so that system protection is performed by a combination of the
limiting circuits of both power amplifier and digital signal processor.
NOTE: Setting limit thresholds to the amplifier input sensitivity is important since this calibrates the output
meter display of the crossover to correspond to the amplifier clip point. This gives the system operator a
direct visual indication as to how hard the system is being operated.
The L-ACOUSTICS LA48a is an excellent power match for the V-DOSC system and power amplifier
clip limiting circuitry is sonically very transparent. The LA48a clip limiter works by monitoring the
output signal and comparing the distortion produced between the input and output of the amplifier. If
the distortion exceeds 1% THD for any reason (voltage or current clipping), the limiter reduces the
input signal proportionally (2 msec attack, 150 msec release). Under normal operation, LA48a clip
limiting is inaudible and L-ACOUSTICS recommends leaving the Channel A and B clip limiters
switched ''on'' (rear panel button depressed) at all times.
Limiter thresholds are user accessible and exact settings will depend on individual engineer
preferences and the type of music or application which, in turn, determines how hard the V-DOSC
system is being operated. When additional protection is desirable, limiter thresholds can be lowered
to match the rms power handling for individual sections according to the tables below:
Table 10: Recommended Limiter Threshold Settings
LIMITER THRESHOLDS CALIBRATED TO RECOMMENDED POWER AMPLIFICATION
(2 x RMS Power Handling for Sub/Low/Mid and 4 x RMS = Peak Power Handling for Hi)
ENCLOSURE NOM LOAD RMS POWER PEAK POWER REC'D POWER EQUIV Vrms dBu EQUIV
LIMITER
MODEL (ohms) (W) (W) (W) (volts) (32 dB gain) SETTING *
SB218 4 1100 4400 2200 93.8 9.62 9 dBu
V-DOSC LO 8 375 1500 750 77.5 7.95 8 dBu
V-DOSC MID 8 600 2400
1200
98.0
10.00 9 dBu
V-DOSC HI 16 300 1200 1200 138.6 13.01 9 dBU
* AMP CLIP IS AT 9.5 dBu
LIMITER THRESHOLDS CALIBRATED TO RMS POWER HANDLING
ENCLOSURE NOM LOAD RMS POWER PEAK POWER RMS POWER EQUIV Vrms dBu EQUIV LIMITER
MODEL (ohms) (W) (W) (W) (volts) (32 dB gain) SETTING
SB218 4 1100 4400 1100 66.3 6.61 6 dBu
V-DOSC LO 8 375 1500
375
54.8
4.94 5 dBu
V-DOSC MID 8 600 2400 600 69.3 6.99 7 dBu
V-DOSC HI 16 300 1200 300 69.3 6.99 7 dBU
NOTE: The LA48 has a comparatively low input sensitivity (9.5 dBu) and, in practice, it can be
necessary to equally scale up the individual crossover channel output gains in order to have sufficient
drive capability (note: this has been done for Version 7 preset library release). It is far better to use
the output drive capability of the DSP digital-to-analog converters (DACs) and analog output section
rather than overdrive the input analog-to-digital converters (ADCs) so do not be afraid to increase the
channel output gains uniformly in order to achieve a comfortable gain structure. Whether this is
necessary will also depend on how ''hot or cold'' the FOH mix engineer likes to run his console. When
in doubt, disconnect all loudspeaker cables and run pink noise from the console at nominal level
through the crossover to the power amplifiers and examine crossover input/output levels, crossover
limiter indicators and amplifier clip indicators to verify system protection and gain structure.