Cable Design


Background

Cable design and performance has been surrounded by controversy amongst audiophiles, most manufacturers claiming enhanced system performance and somehow improving the signal.

Truth is, that all cables degrade the original signal and cables, like all components should be selected by their lack of signal distortion.

This distortion shows itself by either a sonic character change or loss of information; both of these will also depend on the cables suitability within a given system. It is also important that the signal is not corrupted by outside influences such a mains radiated fields or RFI (Radio Frequency Interference). In our research however we have found that while effectively transmitting the signal, equipment performance could be improved when cable earthing allows increased signal flow, reducing signal distortion within the equipment itself, more on this later.


Interconnects

Firstly it must be understood that interconnects perform a completely different task than speaker cable. Interconnects transmit low level signals, whilst speaker cables transmit high level and high current signals and this effects their design. The elements of an interconnect usually consist of a conductor, dielectric, screen, return, sheath and terminations. We will look at each and explain why each is used.


Conductor

The two most common conductor materials in use today are copper and silver. Different processes from annealing to cryogenics alter the conductor performance however tests show that either material has its limitations, especially when transmitting low-level signals. In recent years other materials have been developed which, whilst not offering the same performance in electrical conductivity, offer better performance in how they transfer the multi-octave signal (music) without distortion.

What causes this distortion? Several things; electrical resistance, skin effect, dielectrics and electrical/magnetic fields. In a normal conductor, an electrical signal may be visualised as a sea of electrons moving across a heavy ionic lattice. The electrons are constantly colliding with the ions in the lattice and converted into heat. As a result, the energy carried by the current is constantly being dissipated. This phenomenon is called electrical resistance. Resistance is hardly useless as it allows us the benefits of an electric fire in winter! But for the purpose of a high performance audio conductor it causes problems and signal distortions.

The situation is different in a superconductor. These days research into electrical signal transfer goes beyond simple movement of positive and negative electrons and delves into the subatomic particles of fermions and bosons. For many years it has been known that 'superconductors' have the ability to conduct high levels of current under the right conditions. Under extreme cold and pressure most material can become a superconductor, where molecular vibrations are slowed down sufficiently to facilitate unimpeded electron flow. The characteristics of superconductivity only appear when the temperature is lower than its critical temperature, which is always lower than when we would be frozen solid, not very user friendly. These are mostly called Type I superconductors.

In recent years development in this area has produced what is called Type II superconductors, were the characteristics of superconductivity appear at higher temperatures. Whilst this is still much lower than can be used in domestic situations, some of the properties of superconductivity remain at room temperatures where the signal is very low, most notably a wide linear bandwidth with low distortion. It is this Type II superconductor that is used in the construction of our interconnect cables.


Multistrand or single core?

In our cables we use single core for two reasons; 1. Skin effects and 2. Molecular interference.

All electric currents generate magnetic fields that in turn can affect the current (this is the principle behind electric guitar pickups). With an alternating current (AC) there is a delay in the magnetic field's response to the change in current and the 'old' magnetic field tends to push current towards the outside of the conductor. As frequency increases, so does the effect until at very high frequencies the entire current flows in a very narrow skin on the conductor, hence the name.

Skin effect reduces current density at distances away from the surface, which is true of either single or multistrand cables, and there is some disagreement as to whether it is relevant at audio frequencies, however the size of the conductor is important and if the conductor is small enough it will push skin effect induced audible distortion out of the audio range. In our cables the conductor size has been determined by its sonic benefits, electrical properties and its interaction with other components of the cable design.

We also use a single conductor and not multistrand to avoid electrical distortion caused at the interface when the two conductors come into contact with each other. The conductor as it passes an electric current, generates a magnetic field around its surface. The screen, which surrounds the conductor, also passes an electrical current and generates its own magnetic field. To minimise interaction between these two fields the conductor does not run through the middle of the cable but off centre.


Dielectric

The main conductor is separated from its return or screen with an insulating material, which is called the dielectric. The electrical behaviour of dielectrics in low level signal cable is very important as it acts like a capacitor, absorbing energy from the conductor, which it stores and later releases. The less energy it absorbs the better and energy that is absorbed should convert into heat and not be reflected back to the conductor causing phase and frequency shift problems. The ideal conductor is one with no insulation except for air and we use a pre-extruded PE, which is excellent for this purpose and is larger than the conductor so there is minimal contact with the dielectric, as if suspended in air, and it therefore has little influence on the sonic performance of the conductor.


Direction and 'burn-in'.

Both interconnect and speaker cables are marked for signal direction. As mentioned before the electrical signal is carried with positive and negatively charged electrons, which polarise in a certain direction over time, something commonly referred to as 'burn iní. This affects the cables performance and whilst the cables can be reversed and burnt in the other way, the cables are marked for ease of use. Moving cables from one system to another will also require a burn in period as the electrical properties of the cable conform to the properties of the equipment being use. Again in this opinionated world of audio many people would disagree with this, however our experience both sonically and testing would indicate that this is true.


Return & Screen.

A much-overlooked subject in cable design, but possibly the most important is the return signal.

This not only affects cable performance but the equipment it is connected too. Whilst electrical signals pass through equipment additional noise is produced in the earth supply, which appears as low level noise or electrical hash. Some amplifier manufactures claim to eliminate this, however electron movement will always create this and it will build up within the equipment unless effectively drained. In our interconnect cables the physical amount of material employed assists this process and is partly responsible for the 'inky black' backgrounds commonly associated with our turntables.

Comparisons with other cables can be difficult if not done with care, especially as our cable can improve equipment performance in the short term, therefore if another cable is placed into the system immediately afterwards it will benefit from our cables results.

Another major issue with cables is external interference from RFI or electrical mains. Many times we have experienced radio 'something' from another country, the local taxi company or interference from mains leads attached to equipment. For this reason our SCT Black cables use a full metal jacket screen, giving 99%+ electrical screening and the sonic effect is instantly noticeable. Gone is the high frequency interference which some consider the 'airy sound', images become more distinct and etched in space, improved soundstage, treble less harsh and bass/midrange tighter.


Termination.

This part of the cable is just as important as the other elements involved. The termination plug must form a good non-oxidising contact with the socket and should also provided sufficient contact so that electrical signal can pass unimpeded. As such we use locking WBT connections, which importantly provide a large earth contact area, which becomes more efficient when locked to the socket assisting the flow of negative electrons away from equipment.


Speaker Cable

As mentioned, speaker cable conducts higher voltage and current levels than interconnect, which directly effects design, however our development work on interconnects has influenced our ASC speaker cables.

It's not possible to use the same conductor material as in our interconnects as this is only suitable for low-level signals. The higher current in speaker cables makes it impossible to use a single conductor as the wire gauge would be much thicker and would consequently suffer from electromagnetic flux problems, creating the skin effect and the sonic distortions it would create. As a result we employ several high purity copper wires, each one of these wires within its own dielectric chamber of a larger diameter. This means that most of the wire is suspended in air, the best dielectric, which reduces phase and frequency shift problems associated with dielectrics. As the signal passes through the wire, both on the surface and within its core, it is important that nothing occurs to prevent this. Copper's surface will oxidise over time and as the wire is suspended in air, this will reduced the electrical properties of the wires surface and reduce electron flow, causing distortion, consequently each conductor is gold plated to prevent this problem. An alternative is silver, however this was rejected, as the transmission properties are too dissimilar to copper and would of caused frequency time phasing issues.

An important issue with cables is inductance and capacitance. Reducing these increases bandwidth and frequency response. Within its frequency response an audio cables' capacitance remains fairly constant with frequency, but the inductance in the cable varies with frequency. This is due to the inductance being dependant on the diameter of the conductors and the configuration of the conductors within the cable. These changes in inductance cause audible differences, which will be different with different output/input impedances, hence cables should be suitably match to equipment correctly. When the electromagnetic field (inductance), which varies with frequency, interacts with the electrostatic field (capacitance), this causes different electrical resonances and filtering effects within the cable interface. Depending on the diameter and configuration of the conductors within the cable, the amount of inductance will vary considerably and the sound will be audibly affected.

Using small conductors, openly spaced from each other reduces series inductance, while to reduce parallel capacitance it is necessary to space the positive and negative conductor apart from each other. This will increase the cables bandwidth and improve linearity with frequency, ensuring less system interaction because of the reduced electrical characteristic of the cable, neutrality.

To this end, our wires are held in a 'Litz' type of configuration, where the wires are equally spaced apart, without contact, which also prevents magnetic interaction and surface interface problems, leading to distortions. The positive and negative conductors are also fully screen from each other and from external influence such as RFI and electrical mains, preventing interaction between positive and negative conductors, while making sure the signal remains pure, uninfluenced by external factors.

Our speaker cables are clearly marked for signal direction, as with our interconnects, and recommend a 'burn in' period of at least 72 hours.

As the earth screen would be effectively floating, its potential benefits are not fully used. Our unique earth block, where all screens are connected allows for an independent earth to discharge the screen. This is achieved through our isolated mains plug and links to the cable earth block. Improved bass response and reduced noise levels are achieved, especially noticeable in the midrange and treble. Earthing also reduces the influence of the screens magnetic field on the conductors supporting dielectric, which then further reduces phase and frequency shift issues.

Terminations are just as important as on interconnects. Despite the higher current, signal transfer is vitally important and were possible we would always recommend spade connections as they provide the largest contact area, however locking banana connection offer a small compromise but excellent convenience, especially if they are constantly removed. Either can be supplied with no cost difference.

Lastly, whether to bi-wire or not?

If you can, do it, no question. Bi-wiring substantially reduces distortion, as the cable connected to the treble/midrange no longer has to handle the large magnetic fields caused by the high current needed to supply the bass units. The overall sound will improve, especially in the treble/midrange, which will become more open and transparent, with the bass definition becoming better as its defined in the upper frequencies as with ambience.

What ever your view, concerns, or prejudice, the best proof of the value of well designed and executed cables is to try them for yourself in your given system, until that time you cannot and will not be able to pass judgement of any brand of cable. So life is that simple, listen and judge for yourself, and purchase for the right reason, your musical enjoyment. Unless trophy value is more important to you, we feel you'll enjoy the benefits of our development and the SCT and ASC cables.