Articles and whitepapers

AV Cable and Connectors (8/6/2004)

By Dave Sprake

What are cables and what is their purpose?

In the simplest terms, cables are a conduit for the transfer of signals (analogue and digital) between electronic equipment. Their primary objective is to do this with the minimum of loss and alteration to the signal. Unfortunately, due to a variety of complex electrical interactions, this is often much more difficult than first appears. All cables, to a greater or lesser degree, act as filters due to capacitance and inductance characteristics. This means that they effectively remove often large portions of the transmitted signal, thus minimising picture and sound quality. Over distances of more than five metres, certain types of video cable can 'lose' up to 50% of the sent data. Imagine the detrimental effect this has on the final image quality. Therefore the choice of cable type for wiring any system for audio and video transfer can, and will, determine the overall final result.

As the investment in a home theatre, multiroom or hi-fi system is generally not inconsequential, it is imperative to allocate budget for, and use the highest quality of cabling that is relevant to the particular installation.

Cable and signal quality

In practice, there are many determining factors as to how well, i.e. with how little loss, a cable will transfer signal. One of the most influential, and generally destructive factors to signal, is the dielectric quality. The cheaper the dielectric, and consequently the finished cable, the greater the losses generally are. In order of quality, and starting with the worst are the following dielectric materials: PVC, polyethylene, silicone, PTFE, FEP and air. For cost reasons, a large proportion of installations are made with cables that use the first couple of materials. Unlike electronic components, you cannot see the intrinsic values in a piece of wire, but if cheaper cables are used, the overall system will never produce the results of which it is capable.

The vast majority of specialist cable manufacturers use the latter specified dielectric materials. These are significantly more expensive to use, but will virtually always guarantee a significant improvement in quality.

Nordost CinemaFlex loudspeaker cable with FEP dielectric

As well as the qualitative issues regarding the signal conduit, there are many other issues involving signal type which can, and will, have a very great bearing on the overall final quality. This is particularly true of video signals, where the method of processing and outputting the signal will have a significant impact in determining final quality. For example, running component or RGB rather than composite or S-Video will improve the resolution and contrast ratio due to the picture being transmitted in its segregated element form.

Nordost Silver Screen component cables

For digital audio, using a high-quality co-axial connection, rather than an optical cable, will again dramatically improve resolution since the former does not require the degrading conversion from an electrical signal to light and back again.

Nordost MoonGlo digital audio cable

Choosing the right cable

All signal transfer media have limitations. Understanding these and minimising their effects will make the overall qualitative difference to the finished project. Choosing and specifying the many various cables within a wiring loom can, and often is, a daunting task. This procedure can be made easier, and consequently more effective, by prioritising the signal transfer zones. The most important cables are, and will always be, the ones closest to the audio and video source - lose information here and it will be lost forever. To avoid this, determine the primary rooms for sound and vision, and invest more money in the wiring looms for these zones. Where long runs of cabling are required, especially for video signal, invest in the best quality cable, with the lowest available loss - some cables lose up to three times more signal than others! Also, bear in mind that a large proportion of these cables will be secreted within walls, under floors and in ceiling/roof spaces. With the exception of FEP and PTFE, all dielectrics will degrade over time. They will dry out, crack and delaminate - all of which will adversely affect the quality of reproduction.

Whilst using cables that have FEP and PTFE dielectrics may appear to be initially much more expensive, their lifespan will generally be significantly longer, as they are non-hygroscopic, friction resistant and self lubricating. Indeed most cables manufacturers using these materials offer a lifetime warranty.

Recent developments

There are other, newer, signal transfer media that are currently being adopted by a number of manufacturers. These involve moving the signal within the digital domain and having the processing done at the recipient end. These are DVI (Digital Video Interface) and HDMI (High Definition Multimedia Interface). The former only offers video signal transfer, whereas the latter offers video signal (<5GB/s - twice the requirement for high definition television) and up to eight channels of audio for surround sound. Currently, the only issues concerning these media are the questionable levels of loss over any significant distance, and the number of components that currently support the media - although this will dramatically increase over time.

Conclusion

The benefits of using high-quality cabling for all types of signal transfer are obvious - you get the finest resolution of picture and sound. These conduits are the arteries and veins of your installation's heart, and should never be constricted. Using standard, cheap cabling to wire your home entertainment system can be compared to buying a Ferrari, fitting 'remould' tyres and then driving it with the handbrake part way on... and you would never do that, would you?

Dave Sprake is Managing Director of Nordost (UK) Ltd, manufacturer of audio, video and digital cables using FEP dielectrics for all AV, hi-fi and installation applications.

www.nordost.com