Multicore cables get their name from the multiple cores in their construction. The term multicore is used in reference to the standard and not merely as an indication of the number of cables. It is applied only when the number of cores exceeds the usual construction otherwise used in that type of cable. So, if a cable with 14 cores will not be considered multicore if the typical construction in that category has 14 cores. But even a four core cable is deemed multicore if the typical construction has only two.
These cables are used when we need multiple functions from one cable. For instance, in AV cables, we need video and audio cores. A multicore cable has many advantages, the chief being that it combines multiple functions in one cable. In that way it helps us to connect complicated devices with multiple functionalities and save space. There are many places where these cables are used, including AV instruments and medical devices.
Given its wide applicability, it is important to know how to select the right multicore cable. There are two important factors to be considered when selecting multicore cables: signal systemand signal level. Here we see the importance of signal system when electing multicore cables.
There are broadly two types of signal system that we deal with: a balanced system and a system with some amount of unbalance.
Usually an unbalanced system can be identified by the number of connectors. It usually needs two conductors at the connector. This kind of cable connector with conductors, which are connected via two special cores — the signal wire and the ground wire. The signal wire lies at the centre of the cable construction. The ground wire surrounds it. The function of the ground wire here is twofold —it acts as a part carrier for signals, while protecting the main signal carrying core from outside interference.
For instance, it will partially protect an audio carrying core from interferences from outside noise from other devices as well as radio waves. So, it can both carry and reject noise. On the flip side, it can sometimes end up acting as antennae, attracting noise! So, unbalanced cables work great in carrying signals safely, but when their length exceeds the beyond a certain limit (4 to 6 mts), their inability to suppress interference starts to show. This is all the more evident in a more ‘noisy’ environment where interference from multiple sources can disturb the output.
In a balanced cable we have two signal wires instead of one along with the ground wire. Just like the unbalanced system, the ground wire surrounds the signal wires. However, the difference lies in the way the extra signal wire is utilised. Both the signal wires carry the signal, but with reversed polarity. The result is that when these are taken together, the two reversed polarities cancel out each other, leaving silence!
The output instrument reverses the inverted signal, coming back to the original signal. So, why go through the process and hassle of two signal wires only to flip them back? The reason lies in the way the noise is handled! Along with the signal, the wires also carry the noise, only this noise is identical. The signal, which is flipped at the receiving instrument, now cancels out the noise. So, we have the pure original signal with all the noise cancelled out! This makes balanced system more suitable in case of long cable runs.
Balanced or Unbalanced
While it may seem that the balanced system ought be universal, actually they both have their uses. As explained above, an unbalanced system will be perfectly adequate over short distance in most circumstances. We need the balanced system when it is particularly noisy or when it is a long cable run.
One must also keep in mind that a balanced system needs proper gear. The receiving end must be equipped with gear to ‘flip’ the original signal. Hence, a balanced cable cannot be used in a system that is designed for an unbalanced cable. However, the reverse is not true. An unbalanced cable can be used in a balanced system, albeit with less sound quality.
Hence, the presence or need for a balanced or unbalanced cable decides our selection of the multicore cable construction.