Early ISC Speaker Processor
Owner's Information - all models ©2004 ARX®
Introduction
These notes have been compiled for the benefit of owners of older ART/ARX speaker processors. Please pay
close
attention to the section on connecting the I.S.C. leads to the processor. The colour code and channel selection is
particularly critical when putting the system together for the first time.
Severe speaker damage
can be caused by
incorrect wiring. So please, take it easy and check things as you go.
What is I.S.C?
I.S.C stands for
Interactive System Control
, ARX’s innovative Speaker and Electronics Interface.
ISC monitors the output of the power amplifier driving each set of Loudspeaker components and compares this signal
with an internal model of the SOA (safe operating area) of the driver. When the signal applied to the driver tries to
exceed that SOA, the signal is limited or held at a level which is safe for the driver to reproduce. As the driver signal
forms part of a feedback style loop this SOA can never be exceeded.
Why monitor the outputs of the amplifiers?
What interests us is the actual power being applied to loudspeaker components,
not the signal being applied to the input of the Power Amplifier. To measure this
accurately and allow the user their personal choice in Power Amplifiers we have
to access the outputs of the amplifier. This is used as the reference.
What size amplifier do I need?
ARX quote a “recommended minimum amplifier size” - we don’t quote power
handling. The ISC processor determines the amount of power supplied to each
speaker, ensuring this remains within the SOA of the driver. By recommending the minimum amplifier size we are
indicating that this is the
least
amount of available power required for ISC to operate in the way it was designed by ARX
engineers.
For example: If you operated a system from, say, a 100 watt per channel amplifier, and the ISC processor was designed
to begin operation at around the 200 watt level you would find the 100 watt amplifier completely squared off into
clipping (gross overload distortion) before the ISC processor was aware that any action was required, thus for all intents
and purposes cancelling out the system protection.
Where do I put the processor?
The processor is mounted with the Amplifiers in the amp rack. In most applications once the main frequency response
balance is set, system equalization is achieved by a Graphic or Parametric Equalizer, so there is no need to constantly
access the processor.
Channel A level trim
These controls let you adjust the input level to the unit. During normal operation it is set at the maximum (10) position.
Note: this is an attenuator only, not a gain control. Setting this level too low may reduce the headroom in the preceding
equipment.All remaining controls are recessed behind an acrylic security cover. Unscrew the knurled nut at each end of
the cover and lift off to make adjustments.
Low control
This control determines the Low Frequency output of your system. During normal operation it is set at the 0dB (unity)
position (12 o’clock). It also provides up to +6 dB of gain past unity.
Low ISC LED
This LED indicates that the ISC protection circuitry is operating on the Low output. During normal operation this LED
will light up on transients or peaks if the system is being used to achieve high SPL. This is normal, and should not be
taken as an indication that the system is being overdriven. However, if this LED is on for the majority of the time, then
the Low level is too high and should be reduced.
High control and High ISC LED
Same as for Low but applicable to High
VHF level trim control
This control determines the Very High Frequency energy output of your system. It provides control from -12 dB (Hard
LEFT) through to 0 dB/unity (Hard RIGHT). It should be set in the 0 dB position for a flat response, but for a more
musical response you can rotate it anti-clockwise until the desired roll off is achieved.
TYPICAL FRONT PANEL CONTROLS
Part A - Two Way Systems
