Table of Contents
Advertisement
Speaker Wiring
USE THE APPROPRIATE WIRE
For speaker cables, use the largest practical wire size (the
lowest gauge number). Speaker cables, especially for portable
use, should be rugged. The type of wire normally used for
heavy-duty AC power cables ànd utility extensions (such as
for 240-volt industrial power tools). is a good choice; it has
heavy rubber or vinyl outer insulation, stranded conductors,
and is usually fairly flexible. Wire gauge is the most impor-
tant
consideration,
especially
for
long
speaker
cables.
Remember to always calculate the resistance based on twice
the distance to the speaker since the signal must travel up
one conductor and back the other to complete the circuit.
Table 1 shows nominal losses (in dB) for a 30 meter (100 ft)
cable run of different gauges driving a 4, 8, and 16 ohm load.
(Note: since there are 2 conductors,
and the signal flows
through both, the actual round trip cable run is 60 meters or
200 feet.)
For
an
"ideal"
unchanging
load,
these
relationships
are
logarithmic.
However,
for typical speaker
impedances
and
cables,
a linear calculation
will yield a reasonably
close
approximation of the signal loss. Thus 15 meters of wire (50
feet) would give about half the loss shown on the chart, and
so on.
For example,
ten feet of 10-gauge wire driving an
8-ohm studio monitor will produce a loss of 0.022 dB. If the
wire's resistance becomes significant compared to the overall
load impedance, heating will occur in the wire during high
power operation.
|
Large diameter
(small gauge number) wire is expensive, and
long cables made from it are heavy. Rather than running long
speaker cables, it is better to locate power amplifiers near
speakers
and
run
a line-level
signal cable
over
the long
distance to the amplifier. This approach eliminates most of
the
signal
loss due to speaker
cable's
resistance
so the
speakers will be fed al! the amplifier's power without the
need for heavy cables. It can actually save money in many
instances. Where speakers and power amplifiers are located
far away from the signal source (be it a console or a ргеатр),
"balanced line" signal cables are a wise choice.
19
Always use stranded wire for three reasons:
(1) It is more
flexible
and
less prone
to metal-fatigue
breakage.
(2) If an end is nicked while insulation is being stripped for
connection, only one or two strands will break, not the
entire wire, апа...
:
(3) There
is some
evidence,
though
disputed, that higher
frequency audio signals flow along the outside of each
conductor
(skin effect); if this is so, the more strands,
the
lower
the effective
cable
resistance
to high fre-
quencies.
CAUTION
NEVER USE COIL CORDS FOR SPEAKER HOOKUP,
not even temporarily.
Coiled guitar type cords usually
have higher internal resistance than the speakers them-
selves. High resistance is due to the thin wires used to
keep
the coil cords flexible.
These cords will prevent
most of the power from reaching the speakers. іп high
power operation, a coil cord can melt and cause a fire
hazard. As a general rule, guitar-type connecting cords,
both straight and coiled, make poor speaker cables.
CALCULATING SPEAKER SYSTEM LOAD
IMPEDANCES
Several speaker components having the same power handling
capability,
sound
dispersion
angle,
efficiency
or
other
characteristic
are
often
connected
in groups
to
make
a
system
that goes beyond
the capability
of the individual
units in that system.
There are two basic ways to hook up speakers so that power
is uniformly
distributed
and
it remains
relatively easy to
calculate the. resulting load on the amplifier. The easy way to
figure how much power a group of speakers, or drivers, can
handle is to multiply the power handling specification of one
of the drivers by the number of drivers. That part of the
process is always the same as long as all the connected drivers
are identical.
It is not recommended,
nor is it common
practice, to place
different types of bass drivers in a single enclosure, or to
connect different types of bass drivers in series, or parallel
because the power will not be distributed evenly among the
drivers. This same reasoning also applies to the connection of
various systems which have different rated impedances.
A group of speakers that are connected in series presents a
higher impedance
to the amplifier than
any
one of them
alone;
the total
impedance
is the sum
of the individual
impedances. A higher total impedance represents a lesser load
to the amplifier, and consequently
draws
(or receives)
less
power.
Advertisement
Table of Contents
