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A Technical Introduction to Audio Cables

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

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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