Audio multicore cable
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An audio multicore cable is a compact cable, typically about the diameter of a coin, used in the audio recording and entertainment fields, which contains typically 4-64 individual shielded pair microphone cables all housed by one common outer jacket. The name is frequently abbreviated to multicore, multi or core. In North America, the term snake is commonly used.
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[edit] Cable construction
The inner microphone cables are each a pair of insulated, twisted-pair, multi-strand wires, surrounded by shielding made of foil or tightly-braided wire mesh. The cable may be plenum rated making it strong but difficult to handle and roll. More expensive cables use finer wire and wire braid shield rather than foil and the outer jacket is soft making it flexible and easy to roll. A cotton filler runs down the middle of the cable and helps it to maintain its shape. The cable is normally rolled in an over-under manner such that when pulled out of the packer it won't have developed twists.
Different Cable manufacturers use different methods of identification for the shielded pairs of cable. Belden have a sequenced color code and a number for each of the conductors in their products of up to 52 pair cables, for their plenum cables each pair is covered with their patended Belfoil shield, that is only conductive on the inner surface. For their portable cables they use a French Braid. Canare, Mogami, and GEPCO mark numbers on the PVC insulation of the individual pairs.
[edit] Composite multicores
Composite multicores combine different types of signals in the one cable. They may contain coaxial cores for video , twisted pair for data or low voltage cores for mains power. Composite multicores are usually used to connect video cameras, but they are now gaining usage in live sound with the introduction of the Yamaha PM1D which uses a composite cable to connect it to the stage box.
[edit] Audio multicore
The multicore cable runs from the stage box or Microphone Splitter and then to the Front of House sound desk or mixing console. Permanent installations have stage boxes mounted in the floor or side of stage and the cable runs through the roof or floor to the console, located either in the auditorium or the bio-box.
For temporary shows the stage box is placed at the side or rear of the stage and generally 75% of the connectors are female XLR with the balance male XLR. The male XLR are used as returns to the stage for foldback (on-stage monitoring) or FOH at line level. Larger multicores have male and female connectors for each channel at the stage box end giving it more flexibility. In this system the male XLRs may be used to give a split to the foldback desk. The foldback desk is connected by a cable with tails at both ends. The console end always has the opposite sex XLR connector. Larger shows tend to use a system with subsnakes which plug into the main stage box so you can use shorter mic leads on stage and have less clutter.
[edit] Tails
The end of the multicore where the channels fanout is called the tail and it generally goes at the mixing desk end. Tails used to connect a foldback desk to a microphone splitter have all females at one end and all males at the other. Tails used for patching may have male TS or TRS connectors on both ends.
[edit] Breakout cables
An audio multicore may also function as a breakout cable, if it has a compound connector on one end and component connectors on the other. This is more common in short multicores meant for in-studio connections, such as audio engines. 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.
[edit] Multipin multicores
The ideal system uses multipins to connect the subsnakes to the main stage box (which may be rack mounted) and multipins to the main cores. This allows the system to be expanded by channel count or length. The multipin connectors are based on the MIL C5015 standard and are made by companies like Link in Italy or Amphenol in the United States. Alternative connectors like EDAC and Burndy are also used but lack the reliability of the alloy mil-spec style connectors. Examples include;
| Multicore | MIL C5015 Multipin | Sends/Returns |
|---|---|---|
| 8 core | 25 pole | 8/0 |
| 12 core | 37 pole | 8/4 |
| 16 core | 54 pole | 12/4 |
| 24 core | 85 pole | 20/4 |
While the sound reinforcement industry generally uses proprietary multicores depending on the application, the television industry has standardized on a 12-channel snake with a common 36-pin connector on each end known as DT-12. DT-12 snakes are commonly built into sports venues and run from where the TV truck is parked to areas such as the press box or playing field where audio is required by the TV production. The truck can then simply run a DT-12 patch snake between the truck and the house cabling, with actual XLR connectors then only being required at the very end of the snake in order to plug in microphones.
Snake cables can be replaced by using audio over Ethernet, and similar multichannel digital audio technologies such as AES10 (MADI).
[edit] Digital multicores
State of the art systems can now use digital multicore systems whereby the audio signal is encoded to digital using Analog-to-digital converters, the channels are bundled together to be transported on a single wire to a destination then re-converted back to analog using D-to-As. Such systems are branded under names such CobraNet or EtherSound (respectively manufactured by Peak Technologies and Digigram) and licenced to many companies. Sometimes all that is run to the mix positions is control and all audio processing occurs in the Mix Box, or Stage Box.
The main problem with digital multicores is latency, the time taken to encode into digital and then back into analog at the mixing console. Most stand alone digital consoles take their inputs in analog format and the cumulative latency is too great to go unnoticed. The second problem is cost, it is currently much more expensive to use a digital multicore for small systems. Most multicore systems use ethernet wiring as the physical medium, but the system must be as close to synchronous as possible and cannot share the same cable as data systems due to the risk of collisions.
[edit] MADI
[edit] CobraNet
The first viable ethernet based audio multicore suffers from excessive latency and is only really being used for permanent installs. It is acceptable for the sound to the lobby to be delayed from the FOH as you cannot hear the direct sound from stage. CobraNet cards are available for Yamaha digital consoles.
[edit] EtherSound
The most recent ethernet based system is rapidly gaining acceptance for live sound because of its low latency. Ethersound cards are available for Yamaha digital consoles but the slots in Yamaha desks are limited to 16 inputs and outputs. When digital consoles come fitted with EtherSound, digital multicores will gain widespread acceptance.
[edit] Roland RSS Digital Snake
Roland Corporation RSS Digital Snake is a 40-channel digital audio transmission system using one standard CAT 5e cable. It features high quality remote controllable microphone preamps, configurable inputs and outputs and immunity to RF and electrical interference. A remote control unit allows users to easily adjust input gain and also features “scene” recall of preamp settings including level and phantom power status. The system offers built-in cable redundancy, automatically switching to a backup cable should the main cable be compromised. The system inputs can be “split” using approved Ethernet fast switching hubs providing for multiple “transformerless” audio feeds to monitor consoles, recording devices, and broadcast facilities.
