The age-old argument of cable quality has raged between audiophiles for ages. Regardless of whether it is desktop or portable, some enthusiasts argue the quality of the cables is as just as important as the quality of the components in the set-up. Others chose not to indulge and purchase budget cables with the claim that premium cables make no difference to the sound quality whatsoever.
In this article, it is not my intent to address the difference between the two opposing camps but to offer an overview of cable wires jargons and provide insights necessary for your cable buying decisions.
What is earphone cable?
Earphone cable is the wire used to facilitate electrical connections between earphones and sources. As with other electrical cables, the earphone cable is characterised by three key electrical properties: Resistance, Capacitance, and Inductance. Cable ideally needs to be of low resistance, to minimise power loss during transmission.
Resistance and Performance
The resistance of the wire is affected by two key aspects: wire length and the cross-sectional area. The longer the length of the wire is, the more resistance it will have, and therefore the trick is to minimize the wire length required to facilitate different needs.
The cross-sectional area of the wire refers to the thickness of the wire, often referred to as the gauge of the wire. The thicker the wire, the lower the gauge, the lesser the resistance.
Copper is the most widely used material for cable wires due to its low cost and low resistance (1.72 μΩ/cm). The key disadvantage of copper is that when exposed to air, it oxidises and creates copper oxide (yes, the green stuff) which acts as a barrier affecting conductivity.
Silver offers a lower resistance than copper (1.59 μΩ/cm) and is the best conductor, however, the high cost of silver renders silver’s conductivity superiority almost irrelevant, as it offers a scant 8% more conductivity.
Gold has a resistance that’s 1.5 times of silver (2.44 μΩ/cm), however as it does not oxidise, gold is often used for open termination especially in circuit terminations.
More than just natural conductivity
Earlier, we looked at the different materials based on their natural conductivity. Using copper which is the most widely used, let’s take a look at how casting process and its resulting grains’ relationship with distortion.
High Purity Copper has about 1500 grains in each foot (5000/m) which means the signal must cross the junctions between these grains 1500 times in order to travel through one foot of cable. These grain boundaries cause the same type of distortion as current crossing from strand to strand.
Oxygen-Free High-Conductivity (OFHC)
The first grade above normal high purity copper is called Oxygen-Free High-Conductivity (OFHC) copper. OFHC is cast and drawn in a way that minimizes the oxygen content in the copper: approximately 40 PPM (parts per million) for OFHC compared to 235 PPM for normal copper. This drastically reduces the formation of copper oxides within the copper, this copper is not Oxygen-Free, and the correct term used should be Oxygen-Reduced. Coupled with longer gains (about 400 per foot), thus substantially reducing the distortion caused by the grain boundaries.
Linear-Crystal Oxygen-Free (LC-OF)
The next grade is Linear-Crystal Oxygen-Free (LC-OF) copper, also known as Mono-Crystal copper. These copper are cast and drawn in a process that results in only about 70 elongated grains per foot.
Ohno Continuous Casting (OCC)
Patented “UP-OCC” (Ultra Pure Copper by Ohno Continuous Casting Process) by Professor Atsumi Ohno of Chiba Institute of Technology of Japan in 1986, the Ohno Continuous Casting (OCC) is a unique process for casting metals with using a single crystal structure resulting in copper with grains of over 700 feet in length. The unique characteristics of the single crystal copper is that of unidirectional, free of impurity, flexible fatigue-resistance, low electric resistance with no crystal boundaries. This makes it an ideal material for audio application where distortion should be kept to the minimum.
In recent years, the “xN” reference have appeared in advertorials, where the “xN” refers the number of “Nines” of purity of the metal in question: Copper that is 0.9999 pure or 99.99% pure is depicted as “4N” pure.
The nomenclature of xN has no meanings on its own, all else being equal, higher purity is a straightforward benefit. However, grain structure has demonstrated that it can make more difference than an additional “9” or two. UP-OCC where purity can reach 99.9999% (6N) or higher, is probably the best material in a single crystal structure which one can get for audio application.