High-end audio cable
High-end audio cables are intended to improve the sound quality of high-fidelity audio systems. Since the audio signal passes through cables on its way from the source to the amplifier, or from the amp to speakers, the cables will affect that signal. Because audio cables possess known and measurable electrical properties, they will always alter the audio signal some amount. The amount of change will depend upon the design and materials of the cables, the electrical properties of the components on either side of the cables, and the length of the cables.
Controversy
There is controversy surrounding the impact that cables have on audio systems. While it cannot be argued that cables change the audio signal, the audibility of the changes is questioned by some.
On one side of the controversy are some cable manufacturers who are willing to provide evidence of the impact that their cables make. The frequency response plot shown by this cable manufacturer is a direct measurement of the difference that cables can make in the playback of a system. The large high frequency roll-off of the audio signal can be explained by the reactance of the cables used in the system. Reactance is an electrical engineering phenomenon that is a product of energy abosrbtion caused by capacitance and inductance. In short, the reactance of cables will cause them to absorb energy from the audio signal, causing attenuation.
On the other side of the controversy are claims [1] [2] that indicate that even among audiophiles, in a double blind test it is difficult or impossible to distinguish extremely expensive, exotic speaker cables from ordinary lamp cords or budget 12awg copper speaker wire.
It should be noted as potential anecdotal evidence that the audio cable industry has grown substantially over the last 20 years as customers purchase more and more high-end audio cables with the goal of improving their audio systems. In addition, virtually all major high-fidelity audio publications regularly review audio cables for their sonic attributes.
Cable theory
There are almost as many theories as to how an audio cable improves the sound as there are manufacturers.
In his 2001 master’s thesis, “A New Methodology for Audio Frequency Power Amplifier Testing Based on Psychoacoustic Data that Better Correlates with Sound Quality”, Daniel Cheever points out a number of flaws in conventional testing that indicate the ear is extremely sensitive to tiny signals well above the normally-expected range of human hearing. The high-order harmonics to which he refers exert an influence on our perception of the sound that is vastly disproportionate to their strength, to the point that research from as far back as 1937 indicates that high-order harmonics may actually exceed the subjective effect of their lower-order cousins. Since higher-order harmonics can be of much higher frequency and much lower amplitude than normal audio measurements measure, they provide one explanation for the apparent insufficiency of conventional electrical engineering theory in explaining the influence of high-end audio cables. Since this is but one theory, though, it is important that the reader familiarize himself or herself with the basics of audio measurement.
Common theories of cable design
Some manufacturers of low- to medium-end cables as well as do-it-yourself cable designers stick to the basics of capacitance, resistance, and inductance. (Hereafter referred to as a group by LCR, where L is the symbol for inductance and C for capacitance and R for resistance.) They are also noted for their critical approach to selecting materials based on dielectric properties (for insulators) and resistive properties (for conductors) and all electrical properties for geometry.
LCR theory dictates that low-level signal cables such as line-level interconnects be designed to minimize their capacitance and inductance.
The conductors are generally at least made from high-purity copper or even silver. (Some see silver as having a "bright," "harsh" sound with "glare," though this may simply be the synesthetic effect due to the color of the metal. Many silver-based cables have been subjectively reviewed as sounding completely unlike this common characterization.) Often, manufacturers will use oxygen-free, "long-crystal," or high-purity copper, though the particular benefits of these traits in an electrical sense are unproven with regards to audio transmission.
These cable designs are often easy to make at home, with popular "recipes" for budget high-end audio cables published by Jon Risch.
Higher-end cables are often characterized by expensive and exotic materials, as well as exotic geometries. They are usually manufactured for the vendor, whereas many lower-end cables are handmade from raw stock or incorporate ready-made cable types from vendors such as Belden or Canare.
Missing from most of these is the fact that the shield should be connected ONLY at the source end to prevent circulating currents in the shields! This fact is well established in circuits involving critical measurements.