A Technical Introduction to Audio Cables
What is so important about cables anyway?
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.
How a cable itself affects the audio signal
Now, going back to the ways that the cable itself can change
the signal going through it, let's consider both types of
cables separately.
As stated previously, interconnect cables carry a very small
amount of current. Relative to the current the voltage is
large. Because of that fact, capacitance is important, but
inductance is relatively unimportant. As the voltage
oscillates between being positive and negative, the
capacitance slows the voltage changes down, and causes
delays. This can cause audible distortion in the sound.
Because interconnects have very little current, resistance
is not much of a factor. Even an interconnect with extremely
high resistance will only remove an infinitesimally small
amount of energy.
The signal in loudspeaker cables is essentially the opposite
of the signal in interconnects. Both cables have the same
information, but in loudspeaker cables, the voltage is small
and the current is large, relatively speaking. Because of
the high current, both resistance and inductance are
important in loudspeaker cables. The higher the resistance,
the greater the amount of energy that will be absorbed by
the cables. The resistance will not cause any distortion,
but it will decrease the volume of the sound. The inductance
on the other hand, can cause distortion. As the current
oscillates between being positive and negative, the
inductance slows the current changes down, and causes
delays.
How a cable lets outside sources of energy affect the signal
As stated previously, the second fundamental way of altering
a signal passing through an audio cable is to introduce
outside sources of energy. This outside energy is typically
termed "noise". By definition, if any energy is absorbed by
the signal, the signal has been distorted.
There are many potential sources of noise around audio
cables. Some of the more common sources of noise, such as
radio frequency waves, are familiar to most people. When
wiring up a radio, frequently a consumer must attach an
antenna. Antennae are intentionally designed to channel
radio frequency energy into a stereo. Just like an antenna,
it is entirely possible for an audio cable to pick up radio
frequency energy. If you are not intending to listen to the
radio, this is not a welcome effect.
Electronic components, electrical cords, sound waves, and
even the sun, are all capable of creating noise. Electrical
cords create electromagnetic fields around them that can
transfer energy to a cable. Sound waves create mechanical
vibrations that can be transformed into electrical energy
that is added to an audio signal. Because there are so many
different types of noise, there are many methods used to
prevent a cable from picking up noise. Shielding, twisting
of conductors, and mechanical damping are all common noise
protection methods in cables.
While noise affects both interconnects and loudspeaker
cables, generally the effects are far more significant in
interconnects. This is because the signals in the
interconnects have far less energy. Since most forms of
noise are inherently low energy to begin with, this means
that it is far easier for them to modify the low energy
interconnect signals than the high-energy loudspeaker cable
signals.
Macro vs. Micro
The parameters discussed so far have been primarily "macro"
effects. These are for the most part the top-level
parameters that effect cables. These parameters as well as
others not discussed here also exist at a "micro" level.
Taking capacitance as an example, a given cable will have an
overall capacitance that can be measured. This overall
capacitance is a "macro" level parameter. The same cable can
also be analyzed as 1000 separate but connected pieces. Each
piece will have a local capacitance. These local parameters
are "micro" effects and can have their own impact on the
signal separate from the "macro" effects.
The impact that the "micro" level parameters have on an
audio signal is usually less than the impact of the "macro"
level parameters. However, they do still make a difference
in the signal transfer. The various ways that audio
companies choose to either mitigate or ignore these "micro"
level details is, in part, responsible for the vast array of
different cable designs. From cryogenic treatments and
precious metal wires, to fine silk insulation and fluid
filled cable jackets; extreme cable designs abound.
Will I hear the difference?
The fact of the matter is that cables do alter the sound
going through them, and that it is audible. You do not need
to be an expert, or an audiophile, to hear the difference.
To demonstrate this point, simply listen to your stereo. If
you close your eyes, does it sound like the music is being
played live right in front of you? This is what audiophiles
strive for, and unless you have a very high-fidelity system,
your answer to this question will most likely be no. You may
have a hard time describing what exactly does not sound
right about your system, but you know that it doesn't sound
like a live performance.
Of course, the reason why the music does not sound live
cannot be blamed solely on the cables. The degradation of
the sound occurs in every component of your system. However,
the point here is that even a casual listener can detect the
subtle distortions that can prevent music playback from
sounding live. Improving the quality of your audio cables
will improve the sound quality of your system.
It is fairly safe to say that no matter what cable you use,
the modifications to the sound will be small. Audio cables
will never cause a listener to hear a piano when a flute is
being played. However, it is the small detail that makes all
the difference between good and bad quality sound. That is
why very strong opinions are formed about various cables.
As audio systems continue to improve in accuracy, listening
to a "live" performance in your living room gets closer to
reality. Cables are an enabling factor for advancements in
audio reproduction and can play a remarkably important role
in your system.
Written by: Adam Blake CEO / Co-Founder Pear Cable, Inc.
www.pearcable.com
For a more detailed explanation of cable design theory that
Pear Cable thinks is relevant, see the "cable design" white
paper available on pearcable.com
About the Author
Adam Blake is CEO and Co-Founder of Pear Cable, Inc., a manufacturer of high-fidelity audio cables. www.pearcable.com |
