Choosing the Right Audio Cable

One of the most common types of cabling in professional audio systems is a shielded twisted pair. Generally used for mic and line level analog audio it can also be used for AES EBU digital audio. When using a shielded twisted pair for analog mic/line level signals, there are a couple factors to take into consideration, both of which relate to the cables flexibility and durability. We can break this down by the cables intended use. Generally for permanent installations the cable should utilize a foil shield with a UL listed jacket. These cables tend to be less flexible because of the materials utilized to make the jackets. Also, the foil shield offers a more cost effective cable. For portable or live use, the cable should utilize a braided shield, which offers a longer flex life. However, the jacket choice depends on the environment the cable will be used in. If the cable will be used outside it must have a jacket resistant to sunlight and water. This will make the cable less flexible. If the cable will be used for AES EBU signals the most important factor, yet again, is characteristic impedance. These cables should have 110 Ohm characteristic impedance.

A shielded quad conductor is generally used for microphone level signals where external interference is likely to be a problem. When terminated the conductors that are diagonally opposite are connected together. This is done to reduce EMI coupling by making the effective center of each conductor pair the center of the cable. This gives the cable a higher capacitance. Although the number of conductors and their physical relationship improves the cables EMI rejection, it does not make it useful for long runs. The most important aspect of this cable should be its shield. Since these cables are generally used for portable or patching purposes they must be flexible and utilize a braided shield for a long flex life.

2Be Con't...