About Those 'Other' Cables

Remember the old days? When you hooked up your audio with a shielded twisted pair? Some veterans will remember when it was all braid shield, and big bulky cable, before there was even foil shielded cable.
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Remember the old days? When you hooked up your audio with a shielded twisted pair? Some veterans will remember when it was all braid shield, and big bulky cable, before there was even foil shielded cable.

Now you have to choose between braid shields (sure, they still exist) and foil shields, analog or digital, shielded or unshielded (like using UTP data cables to carry audio), and networked formats (like running audio on Ethernet).

Broadcast engineers might be forgiven for finding the choices confusing.

I thought I would make everything just a little worse by mentioning some of the other cables that people use and why.

Multimedia Control

Like MIDI cable. If you're in a rock band or play a synthesizer, this is old stuff. MIDI is "musical instrument digital interface." The cable is one pair for data, and one pair for power. Often, the power pair isn't needed and you only need a data pair. Because the data is kilobits, you could probably use a Dixie cup and a string, so musicians often use mic cable to run MIDI, and it usually works just fine.

MIDI is a control architecture, not a music protocol. It's a way of connecting all these electronic whiz-bangs together. That includes foot pedals, which is where the power+data cables are required, because a foot-pedal rarely supplies power to run itself.

If you are going a long way or you want to install a permanent MIDI cable, buy something with a fire rating (for inside the wall), low capacitance on the data pair and a larger gage for the power pair.

In fact, the limiting factor for MIDI is the power pair. Just like any DC supply, it's the voltage drop that gets you. The data probably could run for hundreds, if not thousands, of feet. So the power pair on these cables is often 18 AWG.

Now if you open a catalog and look for "installable" MIDI, I'd bet you won't find any. Where you will find it is under something like "Multimedia Control" cable or maybe "Musical Instrument" cable. And where these cables are used most often is for touch panel controls, which require, you guessed it, a data pair and a power pair. Cables intended for system brands like AMX Axlink or Crestron CrestNet are exactly that, usually a 22 AWG shielded data pair and an 18 AWG unshielded power pair.

Another cable that might come in handy is another data+power cable, somewhat like the MIDI cable, but in this case we're talking real data (Category 5) and power conductors. The power conductors come in a number of conductors, usually two or four, and a number of gage sizes, 18AWG, 16AWG, even 14 AWG and often four to the bundle.

Now where in the world would someone use four big unshielded wires and a Cat-5? Why, in your ceiling, of course.

IR

This cable is intended to wire up ceiling-mounted speakers with the big unshielded stuff and to connect infrared remote control repeaters with the Cat-5.

You know how hard it is to hit the remote receiver with a remote control. If all you have to do is aim straight up, well, that exactly how you want to hold the remote!

Sure, we're talking kilobits again for the remote control, so Cat-5 is overkill for that. Another application is surveillance cameras, which often are wired with Cat-5 these days. Power and video.

But that doesn't mean it can't be used for something else. Let's say you have an application in which you have some data protocol, network protocol, and you also need to power up the device. This is the perfect cable. And since you know you can use Cat-5 for analog or digital audio, an audio device that needs to be remotely powered also would be a good choice for this cable. And you could do four channels of analog audio or eight channels of AES digital audio on those four data pairs.

You could also use the large wires for speakers, as they were intended. Now you have the inputs and outputs from a power amp.

The only caution I would sound is to make sure the audio pairs are well balanced (good CMRR) so they will reject any bleed from the speaker side.

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