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XLR

The A-Zed of Audio

Lynyrd Skynyrd band logoEvery name has a story; some names have strange ones and others are more boring than you think. The rock group Lynyrd Skynyrd took its name from a high school gym teacher who made a point of enforcing the school’s policy against men wearing their hair long. The rock group changed the vowels and added a D to the end of Leonard Skinner’s name to avoid a lawsuit, and made him the most famous gym teacher in history (and got a ton of mileage out of the letter Y acting as a vowel).

There are other names with less colourful histories which take words and compress them down so they roll off the tongue a little more smoothly – Nabisco, from National Biscuit Company, or Adidas, from the founder’s name: Adolf “Adi” Dassler.

The humble XLR cable, used so commonly in the audio world, is a bit of a surprising acronym, maybe because anything that starts with an X sounds like it should be drinking Red Bull and doing backflips off high cliffs. But as it turns out, the name is a bit of a bore.

The cable was invented by James H. Cannon, and was colloquially known as the Cannon Plug. It’s not such a bad name, since the connector looks a bit like a cannon with its cylindrical barrel. That old name could at least have lent itself to the confabulation of some myth about how the first prototype was made of iron from a cannon whose fuse was lit by General Robert E. Lee during the American Civil War.

But that’s not the case either.

The official name of the Cannon Plug was the X-series. In the 1950s a latching mechanism was added to the cable to avoid it disconnecting accidentally. Shortly after the latch was introduced, rubber was added to surround the female contacts on the cable. And this is how the Cannon X with Latch and Rubber – or XLR cable – was born.

BLT sandwichThe name says exactly what’s there, but in acronym form. It’s like a BLT : no surprises at all, just syllabic efficiency.

An alternative cable was also produced that used plastic for insulation instead of rubber, and was called XLP. You can imagine arriving in an alternate universe where this connection caught on and thinking that someone had stolen the supporting leg from all the Rs. But your anti-self – that is, you but completely opposite and made of anti-matter – would tell you that the P actually stands for plastic and the rubber version never caught on in this world, and he’d pat you on your head at which point there would be the biggest explosion in the universe since the big bang.

Yet before that all happens it’d be good if you have a bit of information about how XLR cables work in this universe so you can at least compare notes with your anti-self before your cataclysmic explosion. 

XLR cableTo start out, XLR cables have male ends and female ends , much like our electrical cables do. The major difference is that the signal flows in the direction that the prongs point. In our electrical system, the electricity flows the other way and for good reason. Can you imagine if the wall had prongs jutting out which would electrocute you if you accidentally brushed past them? This is the sort of world that Red Bull would love to sponsor, but wouldn’t be too fun to live in, especially when fumbling around for a pair of lost sneakers at the back of a dark closet.

Other than the pins showing you clearly which direction the signal flows, what’s nice about XLR cables is that you can couple them together to reach longer distances without buying new cables. Yet sending a signal along a cable for a long distance can be a problem, unless the cable is balanced. Fortunately, XLR cables – like the TRS cables we learned about back in the Jack post – are balanced.

Balanced? We’re talking about cables here, not trapeze artists. But balanced signals are one of the most elegantly simple systems that lets us send clean, loud audio signals from one point to another much like FedEx would have you believe about the work they do.

There are three pins at the end of an XLR cable. Pin 1 is the ground, which sets a reference for the signal. “Ground” can be confusing when you hear it in electrical jargon, but it’s just like in painting – there’s the figure (which is the object of our attention) and the ground, against which the figure is defined. It’s the same thing here, except we’re talking about electrical impulses and not ducks sitting on a pond. 

Milli VanilliPin 2 in the XLR cable sends the signal – let’s imagine our cable is plugged into a microphone (which is the most common XLR use) and the signal is Milli Vanilli lip sync’ing at the other end. Pin 3 sends the exact same signal but inverted. This doesn’t mean that Milli Vanilli is magically singing through pin 3 – that’s impossible because Milli Vanilli never sings. What it means is that the pulses and gaps of the signal are reversed relative to the signal coming through pin 2.

The pins connect to cables which run through the rubber housing that you probably call the cable. So a standard XLR cable is made up of 3 cables. The thing about running metal cables for any length is that unless they’re perfectly shielded – wrapped in lead or some terrible metal and buried deep underground – they act as antennas. The longer they are the more likely they are to pick up interference. 

Although some may argue this point, interference in this case is anything that’s not Milli Vanilli’s beautiful, pitch-perfect lip sync’ing.

When we talk about sound, we’re talking about air molecules that move back and forth. If we have one air molecule moving back-and-forth and another moving forth-and-back by the exact same distance, the two of them are out of phase. If they’re perfectly out of phase you get a much less violent version of the obliteration when matter and anti-matter come into contact – but it’s the same end result: silence.

After Milli Vanillis’ lip sync’ing travels our XLR cable and arrives at the other end, we have two signals perfectly out of phase with one another, and on each signal there’s the exact same interference that has been picked up along the journey, which is perfectly in phase. The final step is you take the inverted signal, flip it around, and combine it with the uninverted signal. The two versions of interference completely cancel each other out, because they’re out of phase. You’re left with a signal that’s louder and punchier than it’d otherwise be because you’ve combined it with another version of itself. In the case of Milli Vanilli, I’m not sure what that actually leaves you with, but you get the idea.

Twisted SisterA balanced signal is a beautiful thing. Instead of developing some insanely complex shielding mechanism to prevent interference from affecting our cables, we run a pair of opposites together and in the end, have a great, clean, beautiful result. Think of that in terms of your old gym teacher who wouldn’t let you have long hair. Maybe he’s not as opposite to you as your anti-self would be but if you can figure out how to do that final flip that balanced signals do, you and your nemesis become a bigger, purer, and better version of what each of you are on your own. As Lynyrd Skynyrd would have it, if you want to be as free as a bird, you have to figure out how that bird can change.


Jordan Mandel is a Creative Media Instructor at the UW Stratford Campus, and writes for this blog regularly. His hobbies include discovering soil acidity testing, odd-numbered pages, and appraising Civil War memorabilia. More of his work can be found at jordanmandel.com/blog, which is home to the award-winning satire rag, The Outa Times.

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