Sound System Design 1295The XLR-type connector is an industry standard for
lo-Z balanced microphones. Unfortunately, in the past,
the wiring of these connectors was not completely stan-
dardized. Although pin 1 on the connector was almost
always connected to the cable shield, some manufac-
turers used pin 2 as high or + and other manufacturers
used pin 3 as high or + (with the remaining pin low
or). Today, most manufacturers use pin 2 as +.
However, older microphones may still use pin 3 as +.
Use of two microphones with different polarity to mic
the same instrument or voice can result in undesirable
phase cancellations. For this reason, it’s wise to check
the polarity of older products.
34.5.1.4.9 Microphone Snake Cables
A snake cable is actually a group of microphone or
line-level cables all in one outer sheath. These cables
use foil shields to reduce their overall diameter to a rea-
sonable size. Because of the fragility of the foil shields
in a snake cable (and because of the high cost per foot),
extra care must be taken in their handling.
34.5.1.4.10 Cable and Connectors for Line-Level
Devices
Line-level devices normally use the same type of cable
and connectors as microphones and other low-level
devices. That is, balanced line-level devices normally
use XLR-type connectors and unbalanced line-level
devices normally use ¼ inch phone plug connectors or
RCA-type phono connectors. Some balanced line-level
devices use three-conductor, ¼ inch tip/ring/sleeve
(T/R/S) connectors.
Like older microphones, the polarity of XLR
connectors on older line-level devices was, unfortu-
nately, not standardized. Either pin 2 or pin 3 may be
the + pin (pin 1 will almost always be the shield).
34.5.1.4.11 Cable and Connectors for Loudspeakers
Loudspeaker cable carries much higher levels of electri-
cal power than either microphone or line-level cable. For
this reason, loudspeaker cables use larger gauge wire.
Typical loudspeaker cable uses anywhere from number
18 gauge wire to as large as number 10 wire (or even
larger). Number 18 gauge wire is suitable only for
low-level loudspeakers (like the hi-fi loudspeakers in
your den). Number 16 gauge wire is suitable for short
runs (less than 25 ft) of low- to medium-level pro-audio
loudspeakers. Number 14 gauge wire is suitable for most
pro-audio work unless loudspeaker runs are longer than
about 75 ft. In that case, number 12 gauge wire should
be used. For very long runs of high-power loudspeaker
cable, use number 10 (or even number 8) wire. A better
way to handle long loudspeaker cable runs, however, is
to move the power amplifier closer to the loudspeakers
and run line-level signals over the long distance. Alter-
nately, use a 70 V (or 100 V) distribution system.
One apparent way to reduce loudspeaker cable
requirements is to use powered loudspeakers that do not
require any loudspeaker cable (only signal cable and ac
power). However, unless ac power already exists at each
loudspeaker location, the ac cable and conduit require-
ments may be more expensive than loudspeaker cable
for nonpowered loudspeakers.
A connector developed by the Neutrik company,
known as the Speakon, has become a de facto standard
among most loudspeaker manufacturers. The Speakon
connector, Fig. 34-57 is, in many ways, an ideal loud-
speaker connector. It is a high-current twist-lock
connector that is unlikely to fall out of its socket. It is
self-wiping to keep its contacts clean. It is easy to
assemble and is made from tough, lightweight plastic.
In addition, it is relatively inexpensive in comparison to
high-current metal connectors.Except for very high-quality types, ¼ inch phone
plugs are not suitable for the high-current use they get in
pro audio. Thus, ¼ inch phone plugs are only suitable for
low- and medium-level loudspeakers (perhaps up to
200 W or so per loudspeaker). Some power amplifier
outputs use dual banana connectors, also called five-way
binding posts. XLR connectors are sometimes used for
loudspeaker connectors, but their current capacity, like
the capacity of a phone plug, is limited, and they should
not be used for higher-power capacity systems.Figure 34-57. The Neutrik Speakon, a four or eight wire,
high-current, twist lock loudspeaker connector. Courtesy
Neutrik USA, Inc.