Monday, April 9, 2012

Cables - Use Them Correctly

I decided to write about this after I saw some classic abuse taking place where I work.  This is not an article about how hard we are on the intern, abuse is our language of love.  In fact if you ever find yourself on a crew and you aren't getting ribbed a little, you're probably about to get voted off the island.  This story does involve the intern though so I'll get on with it.

We were striking a temporary sound and video install for a class and I was helping him peel gaff tape off a temporary bundle he had made up.  I started to focus on what was actually in my hand and it seemed to be an inordinate number of extension cables.  Surely there are some power strips around here?

But upon closer inspection I saw that two of those bright orange puppies had 1/4" ends soldered on them.  I know, I know, somebody probably made those up in a hurry way back when and it saved the day.  I'm hoping that when they were originally made up they weren't being used for LINE LEVEL SIGNAL!!!

There's a reason for all these different types of wires and connectors kids.  Cable for power and speakers is a little more immune to noise and you can get away with just a pair of big conductors inside the jacket.  But when you've got signal that's less than one volt, you need to take a little more care with it.  Instrument or patch cable will at least have the ground braided around the hot wire in the center.  That lets any noise the cable collects drain harmlessly away when it reaches its destination.  Not really, but it helps.  Then you've got balanced cable which has the hot signal, along with that same signal but with the polarity (not phase) inverted and a separate ground braided around the outside.  Between shunting noise to the ground and a little trickery at the input using a transformer or other form of balanced input, you get nice clean signal.

There's a whole lot more to that idea, really there are lots of them that are much better written so take a look around and try and learn something about balanced cables if you're not already in the know.  Next I want to talk about connectors.  My first pet peeve is that because home stereo equipment uses 1/4" jacks for headphones, a TRS jack frequently gets called a stereo jack and a TS jack a mono.  The same connections when used in pro audio equipment (on everything except the headphone jack on a console) uses TRS (tip-ring-sleeve) jacks for balanced connections and TS cables for unbalanced ones.  Beyond that there's a common setup where you can use a TRS jack on a mixer with a Y-cable to create an insert loop.  The point is, it's a lot more complex than just stereo or mono and you should be studied right up on the uses of different connectors before you get your business cards printed up and start offering your services.

And speaking of connectors.  Years back guys that built their own speaker cabinets used to use other types of connectors for their wiring from the amps.  XLR was a common choice because they were a locking connector and could generally handle the wattage.  Also seen is the straight up adaptation of extension cords, Edison ends still on them, for speaker cables.  Yup, just wire the back of your amp rack with outlets and put tails or inlets on your speaker cabinets and you can use any three prong extension cord you want for a speaker cable.  The only problem is that some stage hand can come along and think he's plugging in somebody's amp and send 120 volts directly to your cones.  All sorts of odd possibilities crop up, plug a guitar amp into a PA amp output, do the same with a light, ugh.  Now that self powered speakers are starting to get popular, you just don't need the confusion.  And the good folks over at Neutrik have been kind enough to grace us with Speakon connectors which lock, and are generally only found on amps and speakers.

One last thing and I'll wrap it up.  What most people call an mic connector is actually an XLR connector, specifically a 3-pin version.  There are also versions with four, five and more pins in them.  Four pin can be found in parts of some intercom systems and have been used by color scrollers.  The reason, to keep special cables from being used for the wrong purpose.  Take DMX lighting control for example.  The standard is five pins, but you can buy an adapter that will make it work on 3-pin XLR, in fact a lot of cheap lighting equipment just comes with 3-pin to save you some trouble.  There are two reasons for the 5-pin setup.  The first is so that in complex situations you can actually run a second DMX universe on the extra two pins.  The second is that proper DMX cable has a different impedance than mic cable and in large setups good clean signal becomes really important.  There's also a third reason and it goes back to that unsuspecting stage hand.  Ever try to listen to DMX on a mic input?

I've barely scratched the surface on all the abuses and misuses of cables and connectors here.  I also didn't go very far in setting the record straight.  That's up to you.  I'm just priming the pump here, go do some research on your own so you can grow up big and strong and be a real sound guy some day.  And to those of you wearing knowing smiles right now... my Brethren of the Knob and Fader,  share the knowledge with someone getting started, set em straight before they learn bad habits.

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