One of the most common questions asked by consumers faced
with purchasing cables for their audio or home theater
system is, “What is so important about cables anyway?” They
can cost as much or more than some of the hardware in the
system and to many it is difficult to understand why wire
isn’t just wire.
To begin to understand how audio cables work, we have to
start with the two fundamentally different types of audio
cables you are likely to have in your system. The first type
of cable is called an interconnect, which is used to connect
various components together (such as a CD player to a
receiver). The second type of cable is called the
loudspeaker cable (this is the wire going from the receiver
or amplifier to the speakers). It is important to realize
that both types of cables are carrying the same information,
just with different amounts of energy.
Interconnects carry a signal with very little energy. These
cables only need just enough energy to convey the
information from the source, for example a CD player, to the
amplifier. The low energy requirement means that the signal
in interconnects has very little current (usually in the
range of thousandths of an amp).
Loudspeaker cables on the other hand, carry a large amount
of energy. All of the energy required to move the speaker
cones and make sound must come through the loudspeaker
cables. Because of the high-energy requirement in these
cables the current is relatively high (currents can reach 10
amps or more).
The very basic reason why audio cables are important is
because they change the signal going through them. There are
two different, fundamental ways that an audio cable can
change the signal. The cable itself can change the signal,
or the cable can allow outside sources of energy to change
the signal.
In order to understand how these two situations can occur,
some basic background electrical knowledge is needed.
Signals in all types of wires are conveyed by the
combination of voltage and current. Every signal has some
amount of voltage and some amount of current. The larger the
difference in voltage between two places, say the beginning
and the end of a cable, the larger the amount of current,
and vice-versa. The direct analogy to voltage and current is
the flow of water through a hose. The amount of water
flowing through the hose is analogous to current. The water
pressure in the hose is analogous to voltage. The higher the
amount of water pressure, the more water will flow through
the hose. The higher the amount of voltage, the more current
will flow through the wire.
Every cable has a set of electrical properties that can be
measured using standard electrical testing equipment. The
three most basic properties are resistance, capacitance and
inductance. While a detailed description of these three
different electrical properties is outside the scope of this
article, a basic description of the relevant effects of
these three properties can be given.
– Resistance opposes current. The higher the resistance the
greater the amount of energy that is removed from the current
and turned into heat.
– Capacitance opposes changes in voltage. If a voltage is
increasing, capacitance will cause the voltage to increase
more slowly. If a voltage is decreasing, capacitance will
cause the voltage to decrease more slowly.
– Inductance opposes changes in current. If current is
increasing, inductance will cause the current to increase
more slowly. If current is decreasing, inductance will cause
the current to decrease more slowly.
The final piece of background knowledge that is needed for
this article is what the audio signal looks like. If one
were to take the speaker cover off a speaker to look at the
speaker cone while music is playing, you would see that it
is moving back and forth. In order to move the speaker cone
back and forth, the electrical signal must push and then
pull the cone in rapid and repeating fashion. This is
accomplished by having an Alternating Current, or AC.
Alternating Current simply means that the voltage oscillates
between positive and negative. Because the voltage drives
the current, this means that the current also goes positive
and negative. In other words, the current is going back and
forth in the wire, just like the speaker cone. The subtle
variations in how fast the voltage and current go back and
forth creates the different sounds that we hear when
listening to music. ul3271
