2.1 Unprocessed copper - Tough Pitch Copper (TPC)

Tough Pitch Copper (TPC) is the name given to unmachined copper: it is the type normally used for general purposes and in low cost audio cables. The TPC is melted once, given the cylindrical shape of the conductor (wire), and left to cool. This wire is then repeatedly engraved to reduce it to the desired diameter.

TPC contains between 300 and 500 ppm of oxygen and other impurities, a quantity considered too high for important audio applications. When used for speaker cables or power cables, the result is a loss of fine detail, resulting in an opaque sounding system. This is due to the use of TPC and also, in part, to the quality of PVC insulation used in standard power cables.

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2.2 Oxygen Free Copper (OFC)

Oxygen free copper was designed in Japan around 1975, when it became increasingly apparent that the quality of sound was related to the quality of the copper and the treatment used during the production of the cable.

OFC copper is produced through an extrusion process, which takes place in an inert atmosphere free of oxygen and gas. This leads to a reduction in the content of silver oxide (10 ppm), compared to TPC, and an increase in conductivity measurable between 0.5% and 2% more than TPC. The OFC process, therefore, allows to produce audio cables of much higher quality than the production process used in TPC copper. High purity conductors sound clearer than their TPC counterparts, because there are fewer border areas between the copper crystals, which are the cause of sound degradation. Atlas Performance cables such as Element, Equator and Quadstar use pure OFCs.

2.3 Linear Crystal-Oxygen Free Copper (LC-OFC)

Also around 1975, Hitachi developed its own method for reducing the boundaries between neighbouring veins or crystals. LC-OFC is a production process patented by Hitachi exclusively for their products. After extrusion, the copper wire is reheated, reducing impurities between the boundaries of the crystals, as the copper crystal is arranged with a longer grain. A typical crystal (or grain) in an LC-OFC conductor with a diameter of 1mm is 130mm long compared to the length of only 4mm (typical) in TPC or OFC conductors. At Atlas cables we do not use LC-OFC copper, because we get better results with OCC copper.

2.4 Ohno Continuous Casting copper (Rame OCC)

In 1985, Professor Ohno of the China Institute of Technology developed his own patented method for extruding a grain-free copper wire. (Technical documentation is available from "Japan Inst. Metals" and "Chapman & Hall" publishers)

When a pure metal solidifies, its crystals are arranged following a precise geometric pattern (typical of that metal) radiating from the core, a bit like the dendritic growth pattern typical of trees. The increased size of metal crystals can be varied by repeatedly heating the metal, as is done in the LC-OFC process. The structure of a copper wire can be compared to that of a sugar sachet. Every grain of sugar has a boundary in the crystal. In a conductor, these boundaries of the crystal (potential barriers) act as a non-linear resistance to the passage of electrical current. It follows that the smaller the boundaries, the lower the incidence of the phenomenon on the electrical signal during its propagation from one end of the conductor to the other. The Reference series of Atlas cables, such as Mavros and Ascent, and Superior products, such as Hyper, use OCC copper.

The Ohno continuous casting method reheats the extrusion by releasing the molten copper from the mould, which slowly and gradually pushes down the granule or crystal along the length of the conductor, creating a 'monocrystalline' structure. In reality, as there is no 100% pure copper, there will always be some boundaries, produced by impurities. The frequency of the boundaries created is mostly insignificant. A typical crystal in a copper conductor reduced to 0.3mm using the OCC process has a length of 125 meters!

The advantages are obvious: with almost no boundary between the crystals, the audio signal is no longer hindered in its path along the copper wire and more information and more detail will be faithfully delivered to the receiving device.

Comparison of copper types (diameter 0.3 mm):
 TPCOFCOCC
Purity>99.9%>99.99%>99.999%
Specific gravity8.758.9268.938
Gas impuritiesO2200~500 ppm<10 ppm<5 ppm
H2<0.5 ppm<0.5 ppm<0.35 ppm
Average crystal size0.007 m0.02 m125.00 m
Crystals per meter150500.008

 

2.5 Silver Copper

Apparently good high frequency dynamics are considered typical characteristics of silver plated copper conductors. Silvered copper may give the illusion of bringing back to life an audio system with opaque tones, but this is always at the expense of good bass quality and bass performance. Silver-plated copper cables can also cause fatigue and irritation in the event of prolonged listening. Therefore, we do not recommend using silvered copper, or cables that use two materials with different resistance, both in the signal and speaker cables. It's also a cheap way to produce a signal cable that might initially sound exciting, as we don't want to use it in our home audio systems either, we at Atlas Cables refuse to supply silver-plated copper cables for analogue audio applications; the most frequent complaint we hear from those who contact us is that he's bought silver-plated copper cables and that his system has taken on such a bright and open tone that he can't stand it anymore. Better results are obtained with high quality copper processing and with the use of a dielectric with better properties.

2.6 Pure Silver

Silver, with its lower resistivity, is a better conductor than copper, but any conductor, be it silver or copper, when used in audio applications, must have a cross-section characterized by an adequate area.

Silver is a much more expensive material than copper and, in order to keep costs within reasonable limits, the cross-section area of silver audio cables is often compromised to such an extent that it results in a 'light bass' sound.

Good silver cables, however, are fast, dynamic, and have no interruption throughout the extension of the audio spectrum, providing exceptional detail and instrument resolution.

Atlas Asimi cables use silver OCC conductors and, in the case of the Asimi speaker cable, these conductors have an overall size of 3.5 sq. mm in order to provide high bandwidth definition. Our Asimi is probably the best cable available...anywhere!

The purity of materials used in audio cables

OFC, LC OFC, OCC and silver are conductive materials that, when used in place of TPC, result in greater sound fidelity. However, the choice of conductive materials is only one part of what is involved in the production process of an audio cable with great sonic qualities.

As in the culinary world, the choice of ingredients for a dinner is the sum of individual elements and the level of skill of the cook, which ultimately determine the sensations associated with the meal.

For cables, in addition to the conductor material, there is much more to take into account: there is the purity of the conductor itself, the type of conductor, the speed of propagation, the choice of dielectric, the construction of connectors ...

3.1 All about Nines!

The purity of a conductor is determined by the purity of the ingot from which it is made. The purity of the ingot is closely related to the number of neighbouring grains present in the resulting conductor.

The purity of a conductor is indicated in noni (N). For example, a 99.99% pure ingot will produce a four noni (4N) pure conductor, a 99.9997% pure ingot will produce a five noni (5N) pure conductor and so on. The highest degree of purity for a conductor is 7N (99.99999% purity).

The conductors used by Atlas in OFC-quality audio cables have a purity of 6N. Atlas OCC conductors have a purity equivalent to 7N

 AlSiSCrFeNiZnSeTeAgSbBiPb
4N0.954.79.90.03141.80.260.560.24110.320.151.9
5N0.180.261.1<0.010.03<0.01<0.03<0.05<0.050.1<0.03<0.01<0.01
6N0.040.200.03<0.010.02<0.01<0.03<0.05<0.050.02<0.03<0.01<0.01
7N0.010.030.01<0.01<0.01<0.01<0.03<0.05<0.050.03<0.03<0.01<0.01