thumb|A standard analog multicore cable with 12 sends and 4 returns
An audio multicore cable (often colloquially referred to as a multicore, snake cable or snake) is a thick cable which usually contains 4–64 individual audio cables inside a common, sturdy outer jacket. Audio multicore cables are used to convey many audio signals between two locations, such as in audio recording, sound reinforcement, PA systems and broadcasting. Multicores often route many signals from microphones or musical instruments to a mixing console, and can also carry signals from a mixing console back to speakers.
In audio engineering, the term multicore may refer to the several things:
- an unterminated length of multicore cable intended for analog audio signals (a type of cable harness)
- a terminated cable, with a multipin connector or many individual connectors
- the entire assembly of a terminated multicore cable and stage box
Applications
thumb|Typical live use of a multicore (thick cable on stage)
Multicores usually create a link between the stage and sound desk, or live room and control room. When used in sound reinforcement, the multicore cable runs from the stage box or microphone splitter to the front-of-house sound desk, where it connects to a mixing console. Portable multicore cables, stored loose or on a drum, enable sound systems to be set up at temporary outdoor locations such as music festivals. Permanent installations, especially recording studios, use stage boxes mounted in the floor or walls, with the multicore cable running through the ceiling or false floor.
Without a snake, a rock band performing onstage, for example, would require 20 or more individual microphone cables running from the stage to the mixing console (typically located at the rear of a venue). This would be harder to set up, would cause tangled cables, and it would be difficult to identify each cable.
Varieties
Terminations
Different termination methods can be used on each end to suit the application. When individual connectors are used, three pin XLR connectors are most common, although phone connectors are occasionally used. connectors.
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|+ Example balanced configurations Only 36 pins are used and sometimes the unused pin is omitted. DT12 snakes are commonly built into sports venues and stadiums for easy connection of outside broadcasting trucks.
thumb|right|An analog multicore cable on a reel, showing its EDAC multipin connector.
Subsnakes
A subsnake usually refers to a smaller multicore cable, or one not connected directly to the mixing console. This is more common in short multicores meant for in-studio connections, such as audio engines, analog-to-digital converters or digital mixing consoles. Multicore cables may also connect to either the front or back of patch panels, when the patch panel is used as an access point or breakout box for connecting external inputs and outputs. Some multicore cables designed for unbalanced audio are made, and they contain a number of single-core screened cables.
Core screening
The individual cables inside the multicore are usually screened independently. This reduces crosstalk between cables and also enables each cable to have a screen or ground that is isolated from other cables, significantly reducing the possibility of ground loops which can cause unwanted hum.
A foil-screen is typically used, comprising thin aluminium wrapped around the group of conductors. An uninsulated drain wire is contained inside the screen to facilitate ground connection. A less common construction is a lapped or braided screen comprising thin wires wrapped around the conductors. This gives improved flexibility, but less effective screening.
Core insulation
This describes the method used to isolate the screening between individual cores; two approaches are common. The first method has an extruded plastic sheath around each individual core, making the multicore appear like a number of individual audio cables bundled together inside an outer sheath. The second method dispenses with the individual sheath and typically wraps the screening with very thin plastic; in some cases this plastic is bonded to the foil sheath.
The individually sheathed construction has the advantage that individual cores can easily be terminated to individual connectors at the ends of the cable. Its disadvantage is that the size and weight of the cable are increased. When a cable without individual sheaths has to be terminated to multiple connectors, it is common practice to create individual sheaths using heat-shrinkable tubing.
Overall screening
A small number of multicore cables feature multiple twisted pairs with only a single overall screen. These are virtually obsolete and typically only found in older broadcast installations; the use of individual screens is now virtually standard. Some multicore cables do contain an overall braid screen in addition to the individual screens on each core. This also increases the mechanical durability of the cable.
Overall insulation
Multicore cables usually have a thick PVC or cross-linked polyethylene sheath protecting the bundle of individual cables. The PVC sheath is extruded around the inner cables, and solidifies to hold the cables in a tight group. This stops the cables from coming out of their tight braid (a phenomenon known as corkscrewing), for their plenum cables each pair is covered with their patented Beldfoil shield that is only conductive on the inner surface. For their portable cables they use a French braid. Canare, Mogami, Sometimes the only cable run between the stage and sound desk is a single digital cable, and all audio processing occurs in digital format at the mixing console and stage box.
Common protocols used for digital multicores include audio over Ethernet and AES10 (MADI).