408 Chapter 14
Balanced lines work because they have a transformer
at each end, a device made of two coils of wire wound
together. Many modern devices now use circuits that act
electrically the same as a transformer, an effect called
active balancing. The highest-quality transformers can
be extremely expensive, so high-performing
balanced-line chips have been improving, some getting
very close to the coils-of-wire performance.
It should be noted that virtually all professional
installations use twisted pairs for audio because of their
noise rejection properties. In the consumer world, the
cable has one hot connection and a grounded shield
around it and is called an unbalanced cable. These
cables are effective for only short distances and have no
other inherent noise rejection besides the shield itself.
14.9.1 Multipair
As the name implies, multipair cables contain more than
one pair. Sometimes referred to as multicore cables,
these can just be grouped bare pairs, or each pair could
be individually jacketed, or each pair could be shielded
(shielding is outlined below), or the pairs could even be
individually shielded and jacketed. All of these options
are easily available. Where there is an overall jacket, or
individual jackets for each pair, the jacket material for
each pair is chosen with regard to price, flexibility, rug-
gedness, color, and any other parameter required.
It should be noted that the jackets on pairs, or the
overall jacket, has almost no effect on the performance
of the pairs. One could make a case that, with individu-
ally jacketed pairs, the jacket moves the pairs apart and
therefore improves crosstalk between pairs. It is also
possible that poorly extruded jackets could leak the
chemicals that make up the jacket into the pair they are
protecting, an effect called compound migration, and
therefore affect the performance of the pair.
Table 14-11 shows a common color code for paired
cables where they are simply a bundle of pairs. The
color coding is only to identify the pair and the coloring
of the insulation has no effect on performance. If this
cable were individually jacketed pairs, it would be
likely that the two wires in the pair would be identical
colors such as all black-and-red, and the jackets would
use different colors to identify them as shown in Table
14-12.14.9.2 Analog Multipair Snake CableOriginally designed for the broadcast industry, hard-wire
multipair audio snake cables feature individually
shielded pairs, for optimum noise rejection, and some-
times with individual jackets on each pair for improved
physical protection. These cables are ideal, carrying
multiple line-level or microphone-level signals. They
will also interconnect audio components such as multi-
channel mixers and consoles for recording studios, radio
and television stations, postproduction facilities, and
sound system installations. Snakes offer the following
features:- A variety insulation materials, for low capacitance,
ruggedness, or fire ratings. - Spiral/serve, braid, French BraidTM, or foil shields.
- Jacket and insulation material to meet ruggedness or
NEC flame requirements. - High temperature resistance in some compounds.
- Cold temperature pliability in some compounds.
- Low-profile appearance, based mostly on the gage of
the wires, but also on the insulation.
Table 14-11. Color Codes for Paired Cables (Belden Standard)
Pair
No.Color Combination Pair
No.Color Combination Pair
No.Color Combination Pair
No.Color Combination1 Black/Red 11 Red/Yellow 21 White/Brown 31 Purple/White
2 Black/White 12 Red/Brown 22 White/Orange 32 Purple/Dark Green
3 Black Green 13 Red/Orange 23 Blue/Yellow 33 Purple/Light Blue
4 Black/Blue 14 Green/White 24 Blue/Brown 34 Purple/Yellow
5 Black/Yellow 15 Green/Blue 25 Blue/Orange 35 Purple/Brown
6 Black/Brown 16 Green/Yellow 26 Brown/Yellow 36 Purple/Black
7 Black/Orange 17 Green/Brown 27 Brown/Orange 37 Gray/White
8 Red/White 18 Green/Orange 28 Orange/Yellow
9 Red/Green 19 White/Blue 29 Purple/Orange
10 Red/Blue 20 White/Yellow 30 Purple/Red
Courtesy Belden