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Community VERIS Series - Operation and Installation Manual - Page 20
CONDUCTORS AND INSULATION
Solid conductor wire is slightly less expensive than stranded wire, but much more difficult
to pull through conduit. Also, it does not terminate to most speaker connectors as easily as
stranded wire. Therefore, we recommend using stranded THHN type wire for installations
that involve conduit.
Densely stranded cables, typically used for portable cordage, will coil up easily and lay flat
on the stage, making them a good choice for applications requiring portability such as floor
monitors. Typical examples are 14/2 and 14/4 SJO. Such cable is normally stocked in
many hardware stores.
Wire and cable insulation is always rated for a working voltage and a maximum
temperature. In power distribution systems, wire and cables can get very hot, making the
temperature rating extremely important. When used with loudspeakers, the temperature of
the wire or cable will hardly ever rise more than 10º C above ambient, and voltages will
never exceed 300V (which is the minimum rating of most industrial wire and cable).
Special cables are manufactured for installation in air plenums, while others are made for
direct burial. Use of such products can save a lot of time and expense compared to
installing conduit. However, local, state, or federal building codes may require that
loudspeaker cables are installed in conduits or in cable trays. Therefore, it’s a good idea to
check applicable regulations carefully, before beginning any installation.
In the United States, conductors are sized according to a numbering system know as the
American Wire Gauge, or AWG. Larger numbers, such as #22 or #24 indicate smaller
diameter wire, while smaller numbers such as #10 and #12 indicate larger diameter wire.
In other parts of the world, the metric system is widely used to define conductor diameter.
Metric equivalents can be converted to US AWG sizes, with only a small loss of precision.
The larger the diameter of the conductor, the lower the resistance will be for a given length.
Resistance is normally stated per foot , or per hundred feet of wire. For example, #10
stranded copper THHN has a resistance of .204 ohms per hundred feet, though this can
vary slightly among manufacturers.
The resistance of the wire, the impedance of the load, and the output voltage of the
amplifier will determine how much loss occurs in the wire. These parameters also govern
the damping factor of the amplifier/speaker combination (more on this later).
Below is a table that gives a quick look at the effect of wire size on line loss. These
numbers assume that the amplifier is producing a constant 48 Volts at its output terminals,
which is equivalent to 288 watts into an 8
Ω load or 576 watts into a 4 Ω load:
Size Length Load Z Loss in dB
#10 AWG 100’ 8 Ω -0.42 dB
#10 AWG 200’ 8 Ω -0.83 dB
#10 AWG 100’ 4 Ω -0.83 dB
#10 AWG 200’ 4 Ω -1.58 dB
#12 AWG 100’ 8 Ω -0.66 dB
#12 AWG 200’ 8 Ω -1.28 dB
#12 AWG 100’ 4 Ω -1.28 dB
#12 AWG 200’ 4 Ω -2.39 dB
#14 AWG 100’ 8 Ω -1.03 dB
#14 AWG 200’ 8 Ω -1.95 dB
#14 AWG 100’ 4 Ω -1.95 dB
#14 AWG 200’ 4 Ω -3.55 dB
The worst-case scenario shown above is the 200’ run of #14 AWG into a 4 ohm load. This
will result in a staggering loss of -3.55 dB, or more than half of the amplifier’s total power
output. Use of wire that’s one size smaller, #16 AWG, would cause a power loss of -5.11
dB. This approaches a 75% loss of total available power! As you can readily see, it’s very
important to use the largest gauge wire that you possibly can, particularly when long lines
are unavoidable. Note: NL4-compatible connectors easily accept #12 AWG.