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CHAPTER 3: CAL USER PANEL
The positive (+) and negative (–) pins carry the input as a dif-
ferential signal. The shield (S) pin is connected to earth
through a 1 kOhm, 1000 pF, 15 V clamped network. This cir-
cuitry provides virtual ground lift for audio frequencies while
allowing unwanted signals to bleed to ground. When assem-
bling cables, make sure all three pins are connected on both
ends. Telescopic grounding is not recommended, and short-
ing an input connector pin to the case may cause a ground
loop, resulting in hum.
Looping CAL Loudspeakers
The Analog input connectors allow multiple CAL loudspeak-
ers to be looped from a single audio source. Connect the
loop output pins of the first loudspeaker to the input pins of
the second loudspeaker, and so forth. The loop output pins
are wired in parallel to the input pins and transmit the unbuf-
fered source signal even when the loudspeaker is powered
off.
From audio
To first
source
loudspeaker
To second
loudspeaker
Phoenix cable wired for looped audio
To avoid distortion when looping multiple CAL loudspeak-
ers, make sure the source device can drive the total load
impedance of the looped loudspeakers. In addition, the
source device must be capable of delivering 20 dBV
(10 V rms into 600 ohms) to yield the maximum peak SPL
over the operating bandwidth of the loudspeaker.
To calculate the load impedance for the looped loudspeak-
ers, divide 10 kOhms (the input impedance for a single CAL)
by the number of looped loudspeakers. For example, the
load impedance for 10 CAL loudspeakers is 1000 ohms
(10 kOhms / 10). To drive this number of looped loudspeak-
ers, the source device should have an output impedance of
100 ohms or less.
NOTE:
Most source devices are capable of
driving loads no smaller than 10 times their
output impedance.
16
NOTE:
Make sure that cabling for looped loud-
speakers is wired correctly (shield to shield,
positive to positive, and negative to negative) to pre-
vent the polarity from being reversed. If one or more
loudspeakers in a system have reversed polarity, fre-
quency response and coverage can be significantly
degraded.
Digital AES/EBU (4)
AES/EBU
4
S
+
-
AES/EBU Input Connector
The digital input uses a Phoenix 6-pin male connector and
accepts an AES3 digital audio signal. The digital audio
source is received via the connector's top three pins (shield,
positive, and negative). The connector's bottom three pins
are not used. The pins for the digital connector are clearly
labeled on the CAL user panel.
NOTE:
The AES/EBU port accepts single-
channel (mono) digital audio sources. When
connecting AES/EBU audio sources to CAL, you
must specify in the Compass control software
whether the left channel (AES L) or right channel
(AES R) will be used.
ON/STATUS LED
On/
Status
On/Status LED
During normal operation, CAL's On/Status LED is green. If
the loudspeaker's internal temperature reaches 75° C
(167° F), the LED turns solid yellow and the loudspeaker's
gain is reduced by 3 dB. Though CAL will continue to oper-
ate normally with the lower gain, when the On/Status LED is
yellow, this is an indication that the loudspeaker is reaching
its maximum heat dissipation and a reduction in SPL is rec-
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