Where do you buy your DMX cable?

[alexforey]

I have some Neutrik connectors lying around, and I'm looking to buy a drum/reel of DMX cable. I've seen various options priced around £60 for 100, but they're all black. Anyone know where I can choose the colour (red)? I like being able to identify DMX in my rigs.

[pscandrett]

I'm looking to buy a drum/reel of DMX cable. I've seen various options priced around £60 for 100, but they're all black. Anyone know where I can choose the colour (red)?

I should be in bed, but doing a bit of idle detective work on google led me to this image on White Light's pages: http://www.whitelight.ltd.uk/shop/all-hire-products/data-cables/5-pin-DMX-cable-red-black/

 

Zooming in reveals that it's Tourflex datasafe cable in that image, which means that if you give AC Lighting a ring they should be able to source some red DMX cable for you: http://www.ac-et.com/lighting/products/tourflex_datasafe/index.asp

 

It's quite possible that VDC and other manufacturers will do different colours, but not list them on webpages by default. I'm fairly sure that VDC's AES cable (green) is the same spec/impedance as DMX, for example, as is their LSZH purple AES cable ( http://www.vdctrading.com/shop/van-damme-cable/audio/Digital-Audio-Multicore-Cables-for-AES-EBU-and-Data-plus-Hybrid%20/ ). Try calling round :-) Hope that helps.

[paulears]

As I have loads of different coloured mic cable, I started buying the turquoise can ford cable. It's a bit expensive but has been pretty tough and long lengths seem to be no problem with it.

 

Canford link

[alexforey]

Cool, thanks all. I'll ring AC when I have a moment. If there's no luck there, I've found Thomann have blue, which is OK, but for some reason (given that I'm getting to decide) I have an aversion to blue. Red is much more my style, and looks nice with TRUE1.

[Renny]

No point buying dedicated DMX cable as you don't really need all 5 pins wired.

[david.elsbury]

How many pins are wired isn't the issue- it's the characteristic impedance of the cable....that's quite important (rather than just using mic cable)

[alexforey]

No point buying dedicated DMX cable as you don't really need all 5 pins wired.

 

Pretty much no 120ohm cable comes with 5 pins anyway. There is a big difference between using mic cable with 5-pin XLRs on the end and actual shielded data cable...

[timsabre]

I don't think there is a big difference in how well it actually works.

 

I've been forced to use all sorts of ropey cabling for DMX (even twin and earth once) and as long as all 3 pins are connected it always works. All problems trace back to missing contacts, not type of cable.

[alexforey]

I don't think there is a big difference in how well it actually works.

 

I've been forced to use all sorts of ropey cabling for DMX (even twin and earth once) and as long as all 3 pins are connected it always works. All problems trace back to missing contacts, not type of cable.

 

I've had no end of problems when people run microphone cable as DMX next to dimmed power lines. It costs fractionally more, and I don't think it's worth risking

[peza2010]

I don't think there is a big difference in how well it actually works.

 

I've been forced to use all sorts of ropey cabling for DMX (even twin and earth once) and as long as all 3 pins are connected it always works. All problems trace back to missing contacts, not type of cable.

 

Agreed. Up until a few revisions of our lighting stock ago, all our fixtures were on 3 pin.

 

We didnt have seperate DMX at the time, just used mic cable and it always worked.

[timsabre]

I don't think there is a big difference in how well it actually works.

I've been forced to use all sorts of ropey cabling for DMX (even twin and earth once) and as long as all 3 pins are connected it always works. All problems trace back to missing contacts, not type of cable.

 

I've had no end of problems when people run microphone cable as DMX next to dimmed power lines. It costs fractionally more, and I don't think it's worth risking

 

I would be fairly confident that your problems were not due to the type of cable but were in fact due to one or more faulty cables.

A special "data cable" does not shield interference any better than mic cable does. It's all about cable impedance which affects how accurately the signal travels over long distances, but DMX is relatively slow for data and is not badly affected by the impedance of the cable.

[mackerr]

It's all about cable impedance which affects how accurately the signal travels over long distances, but DMX is relatively slow for data and is not badly affected by the impedance of the cable.

 

Impedance matching does not change how the signal travels over the cable, it affects what happens at the interconnect point. An impedance mismatch (using unknown impedance mic cable) will cause reflections at the point on mismatched impedance. Enough reflections will corrupt the data. Properly matched impedance will not cause the reflection, so will have more reliable performance. In a lighting rig where there may be many DMX interconnects, each one could be adding reflections, and a little more signal corruption. It is not a big financial or effort burden to do it correctly.

 

Mac

[Brian]

Most overall-screened two-core cables, like DMX cable and mic cable, have a pretty poorly controlled characteristic impedance. Because the cores are not held at a fixed distance from each other, but rather move about as the cable bends and twists, the actual impedance is more like a spread of different impedances. As such as long as your terminate with something of about the right value you can improve things enormously.

 

Likewise, unless you are squeezing every last foot out of your runs, cheaper cables, including mic cables, will work just as well as cables labelled DMX cables AS LONG AS YOU TERMINATE. I've seen plenty of DMX cables that are nothing more than mic cables in a different colour and with 'DMX' or 'Digital' printed on the sleeve (and an elevated price tag to match).

 

Where you need long cable runs you should go for a proper low-capacitance cable so as to squeeze every last bit of signal out the other end. But this holds for sound as well; a cable with a high capacitance makes a good LPF for your audio.

 

Like Tim, I've seen plenty of DMX faults which were down to faulty or incorrectly made cables, including brand-new ones.

[timsabre]

Impedance matching does not change how the signal travels over the cable, it affects what happens at the interconnect point.

 

Yes OK I was confusing the explanation of impedance and capacitance in an attempt to keep it simple.

 

I have even found that termination does not change the behaviour in most situations. It's a good way of finding faulty cables though when adding termination makes the whole line die.

In systems where adding a terminator fixes a strange flickery problem, there is usually another issue causing the problem, but often you don't have time to find it.

So I suppose you could say that fitting terminators improves the fault tolerance of the system.

[mackerr]

Most overall-screened two-core cables, like DMX cable and mic cable, have a pretty poorly controlled characteristic impedance. Because the cores are not held at a fixed distance from each other, but rather move about as the cable bends and twists, the actual impedance is more like a spread of different impedances.

 

Maybe true in budget priced cable, but proper DMX cable from a respected manufacturer has a specified characteristic impedance of 110Ω - 120Ω because it does have tightly controlled spacing and twist within the cable. Microphone cable does not generally have a specified impedance because at audio frequencies it is irrelevant, and so the cable is not as carefully constructed and spec'd. With digital audio, and DMX the fast rise time of the signal makes the frequency very high, where the cable becomes a transmission line and impedance matching and line termination becomes important in order to suppress reflections (which can corrupt the signal) back down the cable.

 

Mac