Studio Technologies 240 - Manual (Page 25)

Model 240 User Guide Issue 1, August 2013
Studio Technologies, Inc. Page 25
As noted in the Configuration section of
this guide, each Model 240 is designated
as either secondary or primary. It’s impor-
tant that its companion unit has the opposite
setting. Once the data path has been estab-
lished and power is applied to both units,
mutli-unit operation will automatically take
place.
Grounding and Shielding
As previously discussed in this guide, the
pin 1 connections on the four 3-pin male
XLR connectors associated with the main
outputs are “floating,” i.e., not connected to
anything within the Model 240’s enclosure.
Some audio experts might take offense to
this, complaining that this should have been
left to the user or installer to be connected
or disconnected as desired. However, re-
peated field testing of predecessor products
found that floating pin 1 on these outputs
was often an important part of maintaining
quiet audio. From Fenway Park in Boston, to
the Orange Bowl in Miami, and then north-
west to Husker Stadium on the Nebraska
Plains, lifting pin 1 always did the trick.
A simple solution is available if an applica-
tion does require that a ground be avail-
able on the main outputs’ interconnecting
cables. All Model 240 XLR connectors have
a ground connection that is made to the
interfacing connector’s metal “shell.” And
most XLR connectors have a pin or connec-
tion point available to access its metal shell.
By connecting the cable shield to the mating
connector’s shell terminal, the common con-
nection typically found on audio intercon-
nections is created.
Intercom Channel Crosstalk
By the very nature of its design, a 2-channel
party-line intercom circuit is prone to exhibit
crosstalk. This occurs because the audio
paths are unbalanced (“single-ended”) and
are typically transported on a single shielded
twisted-pair audio cable. The primary causes
of the crosstalk are the common signal
return wire and the capacitance between
the wires in the cable pair. The greater the
capacitance, due to cable type and length,
the more crosstalk there will be. It’s not sur-
prising to find in sports broadcasting venues
that audio from one channel can be heard
“bleeding” into the other channel. Does this
generally create a problem? No. But it can
be a bit unnerving.
There are several ways of reducing inter-
com channel crosstalk. Probably the easi-
est way is to use cable pairs that are not
twisted. Twisted pairs are great for differen-
tial (balanced) signals, but not so great for
unbalanced transmission. This is generally
because the more twists in a pair the greater
the effective cable capacitance. In a stadium
or arena setting, choosing standard “telco”
pairs may actually work better than “high-
performance” audio or data cable!
Another option is to use two cable pairs
for each intercom circuit. If the pairs are
not shielded the wiring is simple. Common
would be connected to one side of each pair,
and then signal from each channel would
connect to the other side of the pairs. If the
pairs also contain shields the wiring could be
done somewhat differently. One option is to
connect common to both cable shields, inter-
com channel 1 (DC with audio) to one full
pair, and intercom channel 2 to the second
full pair. A better option might be to have
common connect to both shields and one
side of the pair that serves channel 2.
Intercom Audio Levels
The Model 240 was designed to function
well with intercom circuits associated with
standard broadcast and production party-
line (“PL”) intercom systems. These systems