1318 Chapter 34
with internal amplifiers and often with internal DSP
signal processing, which may include crossover, delay,
limiting, and equalization. If designed for portable use
(and suspension), these systems can eliminate the need
to carry racks of amplifiers and signal-processing gear.
However, they complicate suspended system design
because ac cabling must be included in the array.
34.6.1.3 Portable System Rigging
Rigging a portable system is much like rigging a perma-
nently installed system (see Section 34.5.3). Do not sus-
pend any loudspeaker system unless its manufacturer has
certified it for suspension. Get the entire rigging system
approved by a licensed architect or professional engineer
(PE). For each new venue, consult with the building
architect or a local PE to confirm that the building struc-
ture is capable of supporting the system with adequate
design factor (safety factor). Have the system rigging
performed by certified rigging professionals.
34.6.1.4 Cabling
The cabling system for a portable system must be every
bit as rugged and efficient as the packaging for the loud-
speaker systems. Solid-core wire is absolutely out of
consideration. High-quality, multistrand wire of a large
wire size (low gauge number) is highly recommended.
Loudspeaker connectors must be rugged, high
capacity, and easy to connect (but difficult to connect
improperly!). While smaller portable systems may
utilize high-current phone plugs, most larger systems
use a specialty type of twist-lock loudspeaker connector,
manufactured by Neutrik and known as the Speakon.
Some amplifiers even have Speakon connections.
Microphone and line-level signals require equally
rugged cable with the addition of a high-quality shield.
Wire must be stranded, and the shield should be a tight
braid of stranded wire. Foil shields will crack and break
from the continuous flexing of portable use. Micro-
phone cables should have a highly flexible outer sheath.
One exception to this rule is the snake cable, a group of
individually shielded, twisted-pair cables in one outer
sheath. The shields in a snake cable are foil to reduce
the overall diameter of the cable, and the outer sheath is
usually made of vinyl or some other plastic-type mate-
rial that is less flexible than the rubber sheath used on
microphone cables. These compromises demand special
care for the snake cable, especially considering its high
cost per foot. The cable must be coiled carefully in
storage and, when it is in use, a mat or other protection
must be placed over the cable in any area where it might
be walked on.
It’s a common, but risky, practice to run microphone
signals from a stage area to a mixing area through the
same snake cable used to feed line-level signals back to
the stage electronics. The snake provides a trans-
former-like coupling between the inputs and outputs of
the mixer. This can turn the mixer into a high-frequency
oscillator. The reason some popular music systems
seem to operate successfully this way is that the micro-
phone output levels are so high that the mixer gain is
low enough to prevent the oscillation. One low-level
microphone (like an acoustic guitar microphone),
however, is enough to cause the problem. Thus, separate
microphone-level and line-level snakes are recom-
mended. Some cable manufacturers are now offering
snakes that are specifically designed to reduce the prob-
lems caused by running microphone and line-level
signals in the same snake. These may be useful in
portable systems.
Microphone connectors are invariably XLR type for
good reasons. The XLR connector is rugged yet easy to
connect and disconnect. It has ample current capacity
for microphone and line-level signals, and it has limited
self-wiping (cleaning) of its contacts. Furthermore,
pin 1 of the XLR always connects first. This allows the
shields of the cables being connected to equalize their
static charge before the signal wires are connected and
thus helps avoid electrical (static discharge) transients.
Snakes with only a few cables are often terminated with
a group of individual XLR connectors. Larger snake
cables often have elaborate multipin connectors that
lead to either a group of XLRs or a metal box with a
group of chassis-mounted XLRs. Some tour companies
have adapted their mixers to accept a multipin snake
cable directly. This simplifies connections but elimi-
nates the ability to repatch the cables (at least at the
mixer) for a different stage setup, and it hinders quick
troubleshooting.
Digital cabling for sound systems borrows from
computer network standards. Unfortunately, computer
networking connectors such as RJ45 (Ethernet) and
fiber-optic connectors, are not rugged enough for
constant portable usage. Some manufacturers now offer
ruggedized versions of these connectors, Fig. 34-56, and
more such connectors will certainly appear in the future.