A Technical Introduction to Audio Cables
What is so important about cables anyway?
One of 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 hardware in 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 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 loudspeaker cable (this is wire going from receiver or amplifier to speakers). It is important to realize that both types of cables are carrying 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 information from source, for example a CD player, to amplifier. The low energy requirement means that signal in interconnects has very little current (usually in range of thousandths of an amp).
Loudspeaker cables on other hand, carry a large amount of energy. All of energy required to move speaker cones and make sound must come through loudspeaker cables. Because of high-energy requirement in these cables current is relatively high (currents can reach 10 amps or more).
The very basic reason why audio cables are important is because they change signal going through them. There are two different, fundamental ways that an audio cable can change signal. The cable itself can change signal, or cable can allow outside sources of energy to change 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 combination of voltage and current. Every signal has some amount of voltage and some amount of current. The larger difference in voltage between two places, say beginning and end of a cable, larger amount of current, and vice-versa. The direct analogy to voltage and current is flow of water through a hose. The amount of water flowing through hose is analogous to current. The water pressure in hose is analogous to voltage. The higher amount of water pressure, more water will flow through hose. The higher amount of voltage, more current will flow through 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 scope of this article, a basic description of relevant effects of these three properties can be given.
- Resistance opposes current. The higher resistance greater amount of energy that is removed from current and turned into heat.
- Capacitance opposes changes in voltage. If a voltage is increasing, capacitance will cause voltage to increase more slowly. If a voltage is decreasing, capacitance will cause voltage to decrease more slowly.
- Inductance opposes changes in current. If current is increasing, inductance will cause current to increase more slowly. If current is decreasing, inductance will cause current to decrease more slowly.
The final piece of background knowledge that is needed for this article is what audio signal looks like. If one were to take speaker cover off a speaker to look at speaker cone while music is playing, you would see that it is moving back and forth. In order to move speaker cone back and forth, electrical signal must push and then pull cone in rapid and repeating fashion. This is accomplished by having an Alternating Current, or AC. Alternating Current simply means that voltage oscillates between positive and negative. Because voltage drives current, this means that current also goes positive and negative. In other words, current is going back and forth in wire, just like speaker cone. The subtle variations in how fast voltage and current go back and forth creates different sounds that we hear when listening to music.
How a cable itself affects audio signal
Now, going back to ways that cable itself can change 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 current voltage is large. Because of that fact, capacitance is important, but inductance is relatively unimportant. As voltage oscillates between being positive and negative, capacitance slows voltage changes down, and causes delays. This can cause audible distortion in 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 opposite of signal in interconnects. Both cables have same information, but in loudspeaker cables, voltage is small and current is large, relatively speaking. Because of high current, both resistance and inductance are important in loudspeaker cables. The higher resistance, greater amount of energy that will be absorbed by cables. The resistance will not cause any distortion, but it will decrease volume of sound. The inductance on other hand, can cause distortion. As current oscillates between being positive and negative, inductance slows current changes down, and causes delays.