Articles and whitepapers

Wiring for High-Quality Audio (3/11/2005)

By Darren Smith, Clearer Audio

As wireless technology has advanced, so too has its use in home entertainment - especially with digital audio systems that give access to a wealth of music at the touch of a button. Wireless solutions remain however, relatively expensive, and are prone to limitations. Audio performance can not only be affected by the technology itself, but by certain building materials that can restrict the wireless radio waves, and by interference from other wireless systems as well as electromagnetic interference (EMI).

Cables on the other hand, offer far greater audio performance and reliability. Having dedicated cabling installed is also desirable, and can increase the value of a property.

Types of cable

When wiring a house for audio, the main considerations are which rooms require audio. However many this is, it is always best to have the main audio equipment such as the CD player, amplifiers etc, located in, or as close as possible to, the main listening room. This ensures that the shortest cable lengths are used, resulting in considerably better audio performance.

There are many different types of audio cable available, but the most common types are analogue and digital interconnects and speaker cables. Interconnects are used to transmit either analogue or digital audio signals, and can be unbalanced, pseudo-balanced or balanced.

Unbalanced cable

Unbalanced interconnects (often referred to as coaxial interconnects) are the most common, and are used in both the analogue and digital domains. In the coaxial design, an inner signal conductor is referenced to 'ground' via a concentric, cylindrical outer conductor (screen) which also acts as a shield against unwanted radio frequency interference (RFI). Any interference however, that results in induced current flowing through the screen conductor, will result in these currents being added to the audio signal. Thus, although the cable is screened, an unbalanced cable offers very little protection from such interference.

Pseudo-balanced cable

A pseudo-balanced interconnect uses identical conductors to carry both the signal and ground, but the dedicated ground conductors have been electrically connected to the shield at the source end. This results in an active grounded shield, resulting in significant EMI and RFI noise rejection and significant improvements in sound quality over unbalanced cables.

Balanced cable

A balanced cable has two inner conductors (often referred to as hot and cold). These carry the same audio signal which is in anti-phase, as well as a ground wire and/or a separate braided screen which acts as a shield. The braided screen is grounded, but unlike the unbalanced cable, the screen is not a part of the signal path. Thus any interference that makes it to the screen will not affect the signal directly, and if it is going to externally influence the signal, it will be cancelled out. Balanced interconnects use an XLR plug and will only work with equipment that accepts this type of plug.

XLR connector

As a result of the better noise cancellation, a balanced interconnect almost always sounds better than an unbalanced one. There are exceptions however. An unbalanced interconnect can sound better if the equipment is not truly balanced in design, but uses phase splitters and unbalancing amplifiers to convert an unbalanced signal into a balanced one.

Diagram showing properties of unbalanced cable and balanced cable.

Optical digital interconnects

Optical digital interconnects use an optical fibre to transmit the digital signal in the form of light pulses. The main disadvantage is that it requires conversion from an electrical digital signal to light pulses and back again, which results in degradation of the signal and consequently poorer audio performance. It is therefore best to use a coaxial digital interconnect instead.

Speaker cables

Speaker cables come in many different configurations and their performance depends on a number of general factors. As with all audio cables, speaker cables should be low in resistance and capacitance, especially when used in long runs. Some speakers can also be bi-wired, i.e. two lengths of speaker cable are run to drive the treble and bass drivers respectively. While this results in better audio performance, it also doubles the cost of speaker cabling, so in multiroom installations, it may be more cost-effective to bi-wire the main listening room(s) and single-wire other less important ones.

Cable performance

There are many factors that can affect an audio cable's performance, but most critical are conductor material, dielectric material, geometry, shielding and connections.

The most common conductor used in audio cables is copper - a relatively cheap yet highly-conductive material. To increase performance, the conductor in some audio cables is silver-plated, since silver is more conductive than copper. Indeed the very best audio cables are made from pure silver. Whatever the conductor material used, it must be at least oxygen-free copper (OFC) with a purity of 99.9%. Conductors such as linear crystal oxygen free copper (LC-OFC) and Ohno Continuous Casting (OCC) reduce the grain boundaries in the material and offer even greater levels of purity (typically 99.999%, but sometimes 99.9999%) and consequently better audio performance.

The Clearer Audio Silver-line Optimus Interconnect Cable with Super-Pure Silver (99.9999%), FPE insulation and Eichmann Silver Bullet RCA plugs.

Dielectrics (insulation) significantly affect sound quality. Many audio cables use polyvinylchloride (PVC) because it is cheap, but it offers poor audio performance due to a high dielectric constant. The dielectric constant is the amount of electrical energy stored in a dielectric. The higher the constant, the higher the electrical energy storage, the less audio signal will get through to its destination. Where possible, opt for (in order of performance): foamed polyethylene (FPE), polyethylene (PE), polytetraflurothelene (PTFE - Teflon) or Fluorinated Ethylene Propylene (FEP - Teflon).

Dielectric constant and dissipation factor/losses for common dielectric insulators.

There are many different types of geometry, and each one can affect the performance of an audio cable. The most common is a twisted-pair design. This reduces cable inductance and the effects of RFI - both important advantages for long cable runs. Twisting does however, tend to increase cable capacitance, although this can be minimised through the geometry design.

The environment around us is full of EMI and the subtype RFI, caused by a multitude of devices such as radio transmitters, mobile phones, electrical appliances, fluorescent lights, dimmer switches, thermostats, computers, wireless devices and broadband Internet connections. Such interference can adversely affect the performance of any type of cable, so proper shielding is of critical importance. Without this, all other aspects of cable design are of little consequence. What is the use of high-purity conductors if they can be easily contaminated with noise?

Spectrum of electromagnetic frequency and radio frequency.

Connections

There are many different types of connector available for various applications. Analogue interconnects can be terminated with RCA (for unbalanced and pseudo-balanced configurations) or XLR connectors (for balanced configurations). Digital interconnects can also be terminated with RCA connectors (for unbalanced 75-ohm coaxial cable) but they must be impedance-matched to prevent data loss. Less common are BNC connections (also for unbalanced 75-ohm coaxial cable) which offer a more secure locking termination. Digital interconnects can be terminated with XLR connectors (for balanced 110-ohm cable) although this is mainly used in professional applications for the AE3 digital standard. Speaker cables can be terminated with a variety of different types of connector, but the main ones are 4mm banana plugs, spades and BFA (also known as camcon) connectors. Banana plugs are the most common type of connector but spades offer a better airtight connection.

RCA connectors

Banana plugs

Spades

BFA connectors

The importance of good connectors is often overlooked as they are the final link in the signal path. Poor-quality ones, such as the commonly-used low-conductive gold- or nickel-plated brass, will act like a bottle-neck for the audio signal, restricting electron flow. Any audio connector, be it RCA or spade, should be made from gold-plated copper (ideally oxygen-free copper with a minimum purity of 99.9%) which will give optimum signal transmission and prevent long-term oxidisation.

Long cable runs

Finally, for very long cable runs, it is imperative that the highest quality cable be used. Cables over long runs should always be shielded to ensure minimum interference from EMI and RFI. Most interconnects are shielded, but if possible, opt for pseudo-balanced cables instead of unbalanced cables as this gives significantly better shielding. Another critical factor here is the type of dielectric used. Cheaper dielectrics such as PVC offer very poor performance, even in short runs, and when used in long runs, result in significant signal loss.

Summary

A home that is properly wired with high-quality audio cable will enjoy reliable, high-performance audio, long-term satisfaction and an increase in value.

When considering wiring a property for audio, the first thing to do is prioritise where your budget should be spent. Spend more on interconnects between critical source components and amplifiers because this is the first link in the audio signal chain. Then focus on speaker cabling. For multiroom systems, always spend more on the main listening room - again first on interconnects, then on speaker cables. You may then, for example, decide to spend less on speaker cabling to in-wall kitchen speakers than on speaker cabling to a reception room that has higher-quality dedicated bookshelf speakers. Whatever you decide, always bear in mind that if you want to gain maximum pleasure from your expensive audio system, don't skimp on the cabling!

Darren Smith is Managing Director of Clearer Audio Ltd, manufacturer of hand-made audio cables which feature advanced materials and shielding technologies.

www.cleareraudio.com