# Quad microphone cable?



## venuetech (Jan 18, 2012)

So i have some bulk Belden 1192a Quad microphone cable with 2 twisted pairs 
At this point I am assuming the correct wiring for 3pin xlr would be something like this.

pin 1 shield 
pin 2 white + blue/white stripe
pin 3 blue + white/blue stripe


cable twisted pairs
1 blue+blue/white
2 white+white/blue

is this the way it should be?


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## MNicolai (Jan 18, 2012)

I use the Whirlwind color code, where:

Pin 1 - Shield
Pin 2 - Whites
Pin 3 - Blues


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## venuetech (Jan 18, 2012)

somehow i do not find that code very descriptive
as there are three wires that involve "blue" and three wires that involve "white" yet i only have four wires
so it is not clear which goes where.
is a pair of "blues" blue+blue/white stripe or is it blue+white/blue stripe? and visa versa for the white?


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## MNicolai (Jan 18, 2012)

The quad cable we have in stock is the Canare stuff, which is actually two blues and two whites. My intuition says for the Belden stuff that has stripes, it would be appropriate to use:

Pin 1 Shield
Pin 2 [White + White (Blue Stripe)]
Pin 3 [Blue + Blue (White Stripe)]

That is what would make sense to me.


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## pmolsonmus (Jan 18, 2012)

This is from one of my fellow mods at recording.org, John Dutton. Some great advise

"Well, I was working with Canare star quad (L-4E5C) today. I had to remind myself about some helpful hints for dealing with the braid. One does not want to cut the braid at all so how to un-braid it? Dental pick. Actually what I have isn't quite a dental pick but it is close and a pick. Carefully cut the sheath and pull that off. Now gently push the braid back and forth a bit to begin to loosen it up. Now use the pick starting from the end and gently pull the braid loose into individual strands. Work all the way back to the sheath. For soldering to both pin 1 and to the connector shell, divide the now unbraided wire into two equal portions and then twist tight & tin the ends. Now is the time to slide any heat shrink on the wires if that is your procedure. Solder to the connector. Pull the shrink up over the prongs and heat slightly. Epoxy can be used instead of shrink tube as desired. Assemble the connector and do the other end. Before soldering any wire on the other end make sure you use a multi meter to not cross any pins. Voila. One professional looking cable. 

In my case I was soldering up a 5 pin XLR cable but the same procedure works for 3 pin XLR or TRS. The difference is you twist both blue wires together as one and both white wires together as one. 

Have fun with cables."


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## 65535 (Jan 18, 2012)

As long as you keep it consistant between the ends of the same cord IMO the color code isn't defined by any standard that I know of.

The Canare quad cable I've used is actually quad twisted and not twisted pair meaning that the 4 conductors are all wrapped together rather than twisted pairs. Twisted pair is used for data and not necessary for audio but works very well.


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## Chris15 (Jan 18, 2012)

As to which colours it is, I can't comment.
But to get the benefits of the Quad configuration, you need to be combinging diagonally opposite wires...

As to opening the braid - A sharp multimeter probe is what I tend to use - generally easier to find in a workshop / tool kit than a toothpick...


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## FMEng (Jan 18, 2012)

65535 said:


> The Canare quad cable I've used is actually quad twisted and not twisted pair meaning that the 4 conductors are all wrapped together rather than twisted pairs. Twisted pair is used for data and not necessary for audio but works very well.


 
Twisted pair is essential for the prevention of noise in balanced audio connections. Twisted pair for audio dates back to the creation of the public telephone network. It is how audio can travel on cables for miles without picking up too much noise.

A balanced audio circuit has audio of equal amplitude but opposite polarity on the two signal wires. At the input amplifier, the two signals are summed together. When summed, the desired audio signal adds together to double the voltage. Any noise that is equal in amplitude and polarity (or phase if you want to be picky) on the two wires adds to zero (gets cancelled). The noise reduction of a balanced circuit is called common-mode-rejection. By twisting the wires, any noise that gets induced into them should be equal. If the wires were not twisted, a noise source would be induced into each wire at different amplitudes and phases and the input would not cancel it. 

Quad-wire is merely a way of improving common mode rejection. It is comparable to twisting a single pair tighter, in effect ensuring that the noise is identical on both halves of the input amplifier. It comes at a small price because quad cable has more capacitance that can load the source which causes high frequency losses on longer cables. In most cases, the limitation to common mode rejection is the input circuit design, not the cable. I don't recall ever noticing any kind of improvement from quad mic cable.

Most people assume that the shield does most of the work of preventing noise pickup. It doesn't. A well balanced audio circuit can work perfectly without a shield at all. It just takes well designed output and input stages along with properly twisted pairs in the cable.


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## museav (Jan 18, 2012)

FMEng said:


> A balanced audio circuit has audio of equal amplitude but opposite polarity on the two signal wires. At the input amplifier, the two signals are summed together. When summed, the desired audio signal adds together to double the voltage.


Signal symmetry, the same signal on the + being on the - with inverted polarity, is not relevant to the balanced or noise immunity aspects, if it was then you wouldn't get the benefit when there is no audio output, which is typically when any noise would be most critical.


FMEng said:


> Any noise that is equal in amplitude and polarity (or phase if you want to be picky) on the two wires adds to zero (gets cancelled).


It is not being picky, polarity and phase are two completely different things. Polarity is amplitude related while phase is time related. A 180 degree or one half wavelength shift in phase may appear like a polarity inversion for a simple sine or square wave, but they are not the same and the difference is apparent with more complex waveforms.


FMEng said:


> The noise reduction of a balanced circuit is called common-mode-rejection. By twisting the wires, any noise that gets induced into them should be equal. If the wires were not twisted, a noise source would be induced into each wire at different amplitudes and phases and the input would not cancel it.


As you noted, differential input provides an output that is based on the difference between the + and - input signals, if the two signals are the same then there is no difference and thus no output. Twisted pairs improve the chances of both conductors being affected equally by any noise source. The circuit being impedance balanced (i.e. both legs with equal impedance to ground and what makes the circuit 'balanced') helps any external noise be induced equally in both conductors. Combine the differential input, twisted pairs and impedance balanced circuit and you get very effective noise reduction without the shield even being relevant. In fact any current in the shield can generate a field that actually induces noise into the other conductors, an effect called Shield Current Induced Noise or SCIN and one reason why cables where the shield surrounds the conductors or the drain wire is twisted with and between the conductors can provide some benefits over a cable with a drain wire that is offset to one side, and thus more likely to induce noise unequally in the two conductors.

This may help for StarQuad, http://www.canare.com/UploadedDocuments/Cat11_p35.pdf.


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## fixitj (Feb 8, 2012)

You want to use one wire from each pair.

So, for Canare star quad blue/blue, and white/white.

For your cable, [which you stated is paired blue, blue w/white stripe, an white, white w/ blue stripe.]
I would pair solids and stripes:
blue and white, 
white w/blue stripe and blue w/white stripe.


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## 65535 (Feb 8, 2012)

If you read the data sheet it says that blue/blue-white are a conductor pair and white/white-blue are the other. You combine opposite conductors.


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## derekleffew (Feb 8, 2012)

Use whatever combination of wires you want. In the end it doesn't matter a hoot. 
http://www.controlbooth.com/forums/...nd-better-help-me-find-out-results-usitt.html .


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## museav (Feb 9, 2012)

derekleffew said:


> Use whatever combination of wires you want. In the end it doesn't matter a hoot.
> http://www.controlbooth.com/forums/...nd-better-help-me-find-out-results-usitt.html .


There seem to actually be two different issues involved. John's test indicated that people did not hear an audible difference with StarQuad cable, however the noise rejection of a twisted pair cable is dependent on how the two conductors relate and that relationship could vary depending on how you pair the cables. In fact, one of the claimed advantages for StarQuad is that the twisted pair of twisted pairs further reduces the differential induced noise compared to standard twisted pair, but getting that benefit, or even the performance of standard twisted pair, requires properly matching the conductors for the two pairs.


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## BNBSound (Feb 13, 2012)

museav said:


> There seem to actually be two different issues involved. John's test indicated that people did not hear an audible difference with StarQuad cable



That's the thing, audible. It might not make a difference on one input. But if you've got 32 or 48 open at once and have to apply any kind of gain to get them all in line you want the absolute quietest signal coming in that you can get. Just opening that many channels on a mixer even with nothing plugged in significantly raises the noise floor. The thing you have to weigh is, is it worth doing on all the inputs or just a couple problem ones, as one poster mentioned the higher capacitance involved which in short, kills the highs.


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## museav (Feb 14, 2012)

BNBSound said:


> That's the thing, audible. It might not make a difference on one input. But if you've got 32 or 48 open at once and have to apply any kind of gain to get them all in line you want the absolute quietest signal coming in that you can get. Just opening that many channels on a mixer even with nothing plugged in significantly raises the noise floor. The thing you have to weigh is, is it worth doing on all the inputs or just a couple problem ones, as one poster mentioned the higher capacitance involved which in short, kills the highs.


The study Derek and I were referring to was testing whether there was an audible difference with StarQuad cable when listening to recordings made using different microphone cables. Because of the test conditions and approach used, the noise resistance of the cables was not really a significant factor as that was not what was being tested.

I agree that levels can be additive with multiple sources, 32 identical sources would nominally be a 15dB increase and 48 sources a 17dB increase, but that is also one reason why you don't usually leave unused channels open.

If you have runs that are hundreds of feet long and a system and listening environment where the resulting low pass filter effect would be audible then the high frequency roll-off resulting from cable capacitance may indeed be something to consider, however for many live sound systems it can be of minimal, if any, practical impact. For example, a quick calculation for an SM58 connected to 100m of West Penn 291 cable indicates a -3dB cutoff of around 53,600Hz and the loss at 20kHz would be essentially inaudible. However, if you had a higher impedance load, longer cable length and/or higher capacitance cable then the effects might become audible within the audio spectrum.

This may be getting into some of those areas where there are valid theoretical effects and even audible effects under some conditions, such as in the studio or monitored on headphones, but those effects may be of limited practical relevance to many 'real world' live sound applications. It is easy to be focused on technical aspects that while valid may have minimal actual impact while neglecting some of the things that may much more significantly affect the results.


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## KevinNRP (Apr 24, 2012)

Any opinions between the Canare star quad (L-4E5C) or the Belden 1192a? Which one do you guys like better for live/recorded audio because I'm looking to get a spool of 500ft?


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