Audio Cable Shielding Explained
Posted: 16 March 2011
Synopsis: Audio shields are one of the most crucial defenses against unwanted noise in your sound system. However, with the different types of audio shield cables, the choice between them can seem daunting. Here, the three main types of audio shield cables are disc
The basic function of an audio cable is, obviously, simple: to transport an audio signal from one point to another. However, there is another component of what we expect of our cables that requires them to also attempt to keep any unwanted noise from entering that original audio signal. And when determining the best type of cable that will fit your needs, the amount of unwanted noise reduction will be a crucial factor.
Unwanted noise typically enters the path of the audio signal by way of radio-frequency interference (RFI) or electromagnetic interference (EMI) along the length of the cable. Naturally, the longer the cable, the higher the probability that interference will join the original audio signal and produce itself in the output source in the form of hum, static, or other unwanted sounds. The defense from RFI and EMI comes in the form of audio cable shields.
Audio cable shielding literally shields the core wires (conductors) that are transporting the original audio sound from outside interference. Cable shields are generally made from copper stands and also perform the function of 'grounding' the audio signal. There are a few types of shielding options you will want to be informed on before deciding which will best suit your particular application.
As its name would suggest, a braided shield protects the original signal conductor by surrounding it with braided copper strands. Advantages to braided shields include the fact that the coverage area the shield protects can be varied depending on the angle of the braiding, the number of picks and the rate at which they are applied. Therefore, the coverage can range from less than 50 percent to nearly 97 percent. Additionally, the coverage is extremely consistent; therefore, it is particularly adept at blocking interference from RFI sources, which have very short wavelengths that can sometimes permeate other kinds of shields.
The two main drawbacks to braided shields come in the forms of cost and flexibility. Braiding the copper strands together require machines that work at relatively low rates of speed because of the intricacy of the process, resulting in higher manufacturing costs. Additionally, while the complexity of the woven braids provides more effective reflectivity of unwanted noise, it also leads to a less flexible cable that is more susceptible to damage by twists or kinks in the cable.
Sometimes known as a spiral-wrapped shield, a serve shield is designed similarly to a braided shield, except that a flat layer made of copper strands is wrapped around the original signal conductor in a single direction. Serve shield cables are more flexible than compared to their braided counterparts and generally more suited for live performances.
Consider the needs of a live guitarist. Part of his performance is trotting up and down the stage, jumping off the drum riser and throwing his guitar in the air. As these activities (even some adventurous) can easily result in the twists and kinks in the cable. The flexibility of a serve shield means that such twists in the cable are far less damaging to the shield, resulting in a cable with a longer lifespan.
The downside is that serve shields will not provide as much protection as braided shields, particularly against RFI—and though they last longer than braided shields in live situations, their shield capabilities are weakened over the lifetime of the cable.
Serve shield cables are also less expensive than braided shields, as the manufacturing process is much shorter and less copper is used.
Foil shields offers maximum protection at 100 percent coverage. The shield achieves this by putting a thin layer of Mylar-backed aluminum foil against a copper drain line. This metal-to-metal contact (provided by shorting fold construction) increases the foil's range of effectiveness to include higher frequencies. While foil shield cables will be lightweight and inexpensive, the copper drain line prevents flexibility and the shield will break down quickly under repeated flexing. Foil shields are generally used on multicore cables and digital audio cables.
Shielding has become one of the most important aspects to consider when building a sound system. And as with most products in the audio world, the best type of shielding for you will be entirely dependent on your specific needs. When it comes down to it, most will require serve shields for live performance needs, while braided or foil may be better for cables that will remain stationary in a home or studio. But equipped the above knowledge, you can quickly have the exact products you require to produce an audio sound system that meets your every need.