PA Basics: The 'Snake'/ Multicore and DI Boxes
Microphones and mixers are -of course- vital, but how they interface with together is down to two key items, the DI Box and Multicore.
The 'Snake'/ Multicore
The names basically describe the long wire which goes from the desk to the front. There's nothing clever about it, if it handles 16 channels then it has 16 cables or 'cores' in it, hence multicore. The 'Snake' is just because it's quite long and snake-like (see how clever sound people are!).
They're often made up of XLR inputs labelled 1 to say 16 with a few other channels called 'returns' or 'auxillarys', probably as instrument jacks. They can all go both ways but the intention is Channels 1 to whatever go to the board and the auxillarys go from the board to the front, eg. for monitors/foldbacks.
A few points:
- It sounds dumb, but try to plug mics into the core as you'd like them on the board, eg. leftmost mic in 1, the next mic over in 2 and so on. This will make your life so much easier.
- Multicores can be heavy, in fact beyond about 20m and half an inch thick core you'll probably need a rig with wheels as you will find it hard to lift
- You most likely to run it along the floor unless you have a strong structural element (like the scaffolding on a lighting rig)
- When connecting to a mixer, it can be tempting to let it hold its own weight but it will slowly ruin the connectors on the mixer and core
- Start at the multicore and go to the microphone, not the other way round. This avoids a big mess of cables at the multicore, which really matters when you're trying to resolve a problem, eg. which channel a mic is really plugged into.
- Try to avoid twisting the multicore too much as the cores are relatively thin inside (they don't have plastic coverings as thick as say a normal XLR cable)
- They're really easy to trip over, so tape it down well or possibly even get a rubber covering for heavy-foot-traffic areas (avoiding them is better)
- If wound onto a holder you'll probably find it's only just big enough and being really neat when you wind it in makes unwinding much easier
DI Boxes
Perhaps the least understood part of sound systems. If you're bored then read up here, but basically you put them between instruments like guitars, keyboards and the desk (well usually the multicore).
DI Boxes do three key things:
- turn an unbalanced signal (which is prone to distortion) to a balanced signal which won't be so easily distorted by interference, so a short cable from the DI box to the instrument is best
- can cut out portions of the signal, eg. low thudding noises the mic accidentally picked up with the button settings. It's also a usual suspect for why something isn't working, i.e. someone hit all the buttons on the DI box.
- as a transformer they cause a physical break between the source and the desk, which means if the source sends a massive electrical signal you're likely to fry the DI box but not the much more expensive desk/speaker/amps, etc. Disclaimer: don't rely on DI boxes of course, good electrical testing is key!
You might be surprised but there are sometimes batteries in DI boxes, usually a 9v, which lasts a lot longer than wireless mic battiers, like a guitar pedal.
Often you'll see a couple input jacks, for example 'Input' and 'Input Thru' for instrument jacks, you'll be best choosing 'Input'.
