DMX cabling

[timmiddleton]

hi

 

what is the max length for DMX cable before it needs to be before the signal attenuates too much?

 

also, is there a difference between 3 and 5 pin DMX or are only 3 pins wired across both systems?

 

I'm mostly a PA guy but im thinking of buying some DMX moving heads + disco effects at some point.

 

thanks in advance

 

Tim

[Brian]

what is the max length for DMX cable before it needs to be before the signal attenuates too much?

assuming you are using proper DMX cable (not mic leads) the spec allows for 1000m as a max. Good practice would be to keep to 500m.

 

also, is there a difference between 3 and 5 pin DMX

 

there is no such thing as 3 pin DMX.

[timmiddleton]

so how come lots of lighting effects have 3-pin XLRs for DMX ins and outs??

[Tom Baldwin]

so how come lots of lighting effects have 3-pin XLRs for DMX ins and outs??

<{POST_SNAPBACK}>

 

Because they've been built down to a price, rather than to a standard.

 

DMX is 5 pins. No ifs, not buts. Anything else is not compliant with the standard. Only the first three pins have a standardised use (at least until the latest revision of the spec).

3 pin connectors carrying a signal which matches the DMX specification present an immediate problem - that someone will use ordinary mic cable to connect the DMX fixtures together. "DMX cable" is built to a higher standard for the fast data transfer, and using mic cable to transmit DMX will, at some point, bite you.

 

P.S. the only other excuse some manufacturers can offer (for older products only) is that they were offering support for both their own (proprietary) protocol and DMX on the same connector - again, re-using the connector was a cost saving exercise. All these protocols have been unsupported for several years, so all new kit with a DMX input should, really should, have a 5 pin XLR (specific installation scenarios exempted).

 

Hope this helps - DMX pedantry is a popular sport around here, but it really does matter, so please humour us

 

Tom

[zackw250]

Not entirely true. DMX can successfully run on 3 or 5 pin DMX. Our automated fixtures (HES Studio Color & Spots) which are high-end products use 3-pin DMX as a standard.

[gareth]

Not entirely true. DMX can successfully run on 3 or 5 pin DMX. Our automated fixtures (HES Studio Color & Spots) which are high-end products use 3-pin DMX as a standard.

<{POST_SNAPBACK}>

You've missed the point. Whether or not it's possible to use 3-pin connectors for DMX (which, as we know, it is) is not the issue here. The point that Brian and Tom were making is that the published document which sets out the standard for the DMX512 protocol is very specific about the connector which should be used - 5-pin XLR, and nothing else.

 

The last part of your post typifies the confusion that abounds over this issue. "High-end products use 3-pin DMX as a standard" - they use 3-pin connectors to carry DMX data, but that is not the DMX512 standard - no ifs, no buts.

 

Of course, now we're starting to move into the realms of DMX over ethernet, RDM and all that sort of stuff, things might begin to get a bit less clear-cut. But in general, you can sum it up very simply - 5-pin XLR conforms to the DMX standard ; 3-pin XLR doesn't.

[vinny baby]

So how come 5pin was made standard wen 3pin is clearly most commonly used?

 

I meen most of my fixtures are 3 pin in and out, some of my higher end fixtures have both 3 and 5 pin in and out, to give both options.

 

every console ive ever had has been 5 pin XLR.

 

Also is there not as much temptation to use mic cable on a 5 pin XLR as there is on a 3 pin?

 

I would have also thought you would have got a better signal contact with a 3 pin XLR, as it has stronger and more contact area than the pins in the 5 pin.

 

Also has anybody actully utilised the the 2 extra pins on a standard 5 pin yet. There was rumors of using them for talkback, or error correction and fault relay?

 

(ps, ive hired equipment and cables in the past from many different, high rep companys, and ive been given DMX leads made from standard mic cable)

 

And the amounts of times ive been told I dont need to use termination!!

 

(always do though)

 

vince

[Andrew C]

You should use proper data cable, but for most relatively small scale shows mic cable will work, and sometimes without termination. Sometimes you can T into a DMX cable to add a fixture, or even to reposition your desk. NOTE WELL THE SOMETIMES.

 

As to manufaturers putting 3 pins on their kit, is this Martin vs "The Rest of the World" issue?

[gareth]

So how come 5pin was made standard wen 3pin is clearly most commonly used?

I have no idea. But 5-pin has been a part of the official standard for about 15 years, so anyone who's released new equipment using 3-pin connectors in that time is not conforming to the standard.

 

Also is there not as much temptation to use mic cable on a 5 pin XLR as there is on a 3 pin?

That's another plus-point for 5-pin connectors. It eoncourages people to use the right cable. As Andrew said, using ordinary mic cable can work. But it's a bit like crossing the road without looking - sometimes you can get lucky and pull it off, other times ........ :D

 

Also has anybody actully utilised the the 2 extra pins on a standard 5 pin yet. There was rumors of using them for talkback, or error correction and fault relay?

Some manufacturers (notably CP/Pulsar on their fixtures, and Avo on their consoles) have done things with pins 4 and 5 - but there's no clearly-defined function for those pins, and standard DMX cable only has pins 1 to 3 wired.

 

(ps, ive hired equipment and cables in the past from many different, high rep companys, and ive been given DMX leads made from standard mic cable)

You certainly wouldn't get that from the White Lights, Stage Electrics's and PRGs of this world!

 

And the amounts of times ive been told I dont need to use termination!!

Same answer as the mic cable issue, really. Things don't necessarily go t*ts-up as soon as you leave a terminator out of the equation - sometimes you can get lucky, sometimes you can come unstuck.

[mattevans]

Can someone suggest a good supplier of quality data cable for making up DMX cables? (using 5-pin Neutrik Connectors of course)

 

Thanks

 

Matt

[Andrew C]

Can someone suggest a good supplier of quality data cable for making up DMX cables? (using 5-pin Neutrik Connectors of course)

 

Thanks

 

Matt

<{POST_SNAPBACK}>

 

Not bought any flexible cable for a long time but as to connectors:-

 

Neutric are very good but, consider DGC (Deltron) too. Priced very competitively £2.95 vs £3.88 at CPC prices. They are all-metal on the outside, and available in all black too.

 

I also mark all my DMX with a coloured ring/strain relief, makes it much easier to spot in a heap of cables.

 

CPC stock code for a 5 pin male CN00327

CPC stock code for a 5 pin female CN00330

[vinny baby]

proper DMX graded cable is available from terralec, at £50 for a 100mtr role.

[colinmonk]

DMX Cable - TMB!

[david.elsbury]

I may get shot for saying this.... bit 110 ohm digital audio cable also works pretty well, becuase it is very close to the DMX 120 ohm specification.... a lot closer than mic cable... so, at work we have a whole lot of these 110ohm cables, and 5-to-3 adaptors... In my opinion it works as well as, if not the same as "proper" DMX cable. But it's not DMX cable. Also, if you must use mic cable, I believe you should stay away from "quad" type mic cable (4 conductors + screen) because it has an even more different capacitance than mic cable...

 

As for pins 4 and 5, I believe that the new DMX-512a standard documents the use of these pins.

 

:blink: David

[kalmatthew]

As for pins 4 and 5, I believe that the new DMX-512a standard documents the use of these pins.

 

<{POST_SNAPBACK}>

 

Actually the DMX/1990 standard documents their use as "optional second Data link Complement (Data 2 -)" and optional second Data link True (Data 2 +)" Therefore Avo would be within the standard, however I dont know about CP/pulsar