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Author Topic: DMX cables  (Read 13371 times)

Micky Basiliere

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Re: DMX cables
« Reply #10 on: November 11, 2010, 10:33:33 am »




Rob Spence wrote on Thu, 11 November 2010 00:13

Micky Basiliere wrote on Thu, 11 November 2010 00:07

I have always used 3 pin mic cables and NEVER had ANY issues! i really think its all cable hype!!! five pin is a different story...any high quality xlr 3 pin would be just fine. AND, using a DMX splitter eliminates the need for terminators

Option I assume. There is no science in your statements.
Connector type is simply a choice you make for the instruments you are using. The cable types are different. Terminators are important. Some times you can get away with out them for short runs.


Using the splitter creates shorter runs...eliminating the need for terminatore.


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Shane Presley

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Re: DMX cables
« Reply #11 on: November 11, 2010, 03:41:06 pm »

The best difference it makes for me is the lighting patch cables are not taken for audio use, and visa versa... I ordered all my DMX in purple, so it's VERY distinct.  This makes trouble shooting, or patching a lot easier than following 2 black mic cables, one audio and one dmx.... As others have said it's a minimal cost difference to use the "correct stuff". Also I've found using a termintor is not needed unless it's needed - if that makes sense... If your fixtures are behaving without termination then don't bother. If they are erratic, then terminate.  

I'll also throw one out to the "no dmx on audio lines" guys... 9 times out of 10, I run the lighting sends, up my audio snake (250ft), before it hits the opto splitter.  Yes the 10th time, it makes noise on the audio, but for the most part it works like a charm... when it doesn't I run 2 x 100ft dmx lines...but that's rare...

Rob Timmerman

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Re: DMX cables
« Reply #12 on: November 11, 2010, 08:11:26 pm »

Rob Spence wrote on Thu, 11 November 2010 00:10

Thomas Bishop wrote on Wed, 10 November 2010 09:55

... and 3-pin DMX is perfectly acceptable for microphone cable.  I have 1000' spool of DMX cable on order to replace all my mic cables, and it's only pennies more than mic cable.

But DMX cable may not be ok for audio.

Different cable for different uses.

Audio cable works ok for DMX use for short runs. Long runs or reliability should use DMX cable.



Why would DMX cable not be ok for audio?
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Micky Basiliere

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Re: DMX cables
« Reply #13 on: November 11, 2010, 09:47:32 pm »

Shane Presley wrote on Thu, 11 November 2010 15:41

The best difference it makes for me is the lighting patch cables are not taken for audio use, and visa versa... I ordered all my DMX in purple, so it's VERY distinct.  This makes trouble shooting, or patching a lot easier than following 2 black mic cables, one audio and one dmx.... As others have said it's a minimal cost difference to use the "correct stuff". Also I've found using a termintor is not needed unless it's needed - if that makes sense... If your fixtures are behaving without termination then don't bother. If they are erratic, then terminate.  

I'll also throw one out to the "no dmx on audio lines" guys... 9 times out of 10, I run the lighting sends, up my audio snake (250ft), before it hits the opto splitter.  Yes the 10th time, it makes noise on the audio, but for the most part it works like a charm... when it doesn't I run 2 x 100ft dmx lines...but that's rare...


I do the opposite...From FOH,from opto splitter(6 sends) out through 150' lighting ONLY snake to stage...NO TERMINATORS(they only cause problems!) I would not recommend sending DMX through an audio snake??? just my 2 cents... Smile
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Tom Bourke

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Re: DMX cables
« Reply #14 on: November 11, 2010, 11:47:48 pm »

Micky Basiliere wrote on Wed, 10 November 2010 23:07

I have always used 3 pin mic cables and NEVER had ANY issues! i really think its all cable hype!!! five pin is a different story...any high quality xlr 3 pin would be just fine. AND, using a DMX splitter eliminates the need for terminators

and
Quote:

I do the opposite...From FOH,from opto splitter(6 sends) out through 150' lighting ONLY snake to stage...NO TERMINATORS(they only cause problems!) I would not recommend sending DMX through an audio snake??? just my 2 cents... Smile


All of this is wrong in my experience.  Audio cables work ok for short run and few instruments.  Once you hit any kind of length or instrument counts signal breaks down.  Worse yet is mixing audio and data cable types in one system.  If a terminator makes things worse you have a problem or 2 some place else.

Every time there is a change in cable type there is a reflection of the signal from that point.  If you have several such changes you have lots of interactions.  A terminator is meant to act as a substitute for an infinite line.  The reason they may or may not cause a problem in a mixed or audio only cable environment is they change how the reflections interact.  Some times they make it worse, some times better. Depends on how the reflection from an unterminated line interacts.  Every output of a splitter should have its own termination.  Don't even think of Y cables.

It is understanding these reflections that explains the erratic nature of DMX problems.  I have seen them on a scope and in video setups.
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Rob Spence

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Re: DMX cables
« Reply #15 on: November 12, 2010, 06:58:54 pm »

Rob Timmerman wrote on Thu, 11 November 2010 20:11

Rob Spence wrote on Thu, 11 November 2010 00:10

Thomas Bishop wrote on Wed, 10 November 2010 09:55

... and 3-pin DMX is perfectly acceptable for microphone cable.  I have 1000' spool of DMX cable on order to replace all my mic cables, and it's only pennies more than mic cable.

But DMX cable may not be ok for audio.

Different cable for different uses.

Audio cable works ok for DMX use for short runs. Long runs or reliability should use DMX cable.



Why would DMX cable not be ok for audio?

Well, for one thing it is the wrong impedance. Why do you think there are multiple kinds of cable?
Heck, my main power feeder has twisted conductors but that doesn't make it ok for mic cable.
So, shielded twisted pair for mic cables is a different impedance than that for DMX because DMX is a digital signal and audio is analog.

An electric circuit such as the input of a mixer is made up of 3 main components. There is the mic, the cable, and the mixer preamp. Together they make a circuit that takes sound waves, generates electricity, transmits it over the wires and into the mixer. For it to work right (meaning get the audio into the mixer without distorting it), all the impedances should be correct. Same goes for other kinds of circuits like TV antenna or WIFI antenna.
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Rob Spence
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Rob Spence

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Re: DMX cables
« Reply #16 on: November 12, 2010, 07:02:17 pm »

Micky Basiliere wrote on Thu, 11 November 2010 10:33




Rob Spence wrote on Thu, 11 November 2010 00:13

Micky Basiliere wrote on Thu, 11 November 2010 00:07

I have always used 3 pin mic cables and NEVER had ANY issues! i really think its all cable hype!!! five pin is a different story...any high quality xlr 3 pin would be just fine. AND, using a DMX splitter eliminates the need for terminators

Option I assume. There is no science in your statements.
Connector type is simply a choice you make for the instruments you are using. The cable types are different. Terminators are important. Some times you can get away with out them for short runs.


Using the splitter creates shorter runs...eliminating the need for terminatore.




Micky, if you are going to quote me, don't put your thoughts in my quote!

If I understand what you meant, yes, the splitter makes shorter runs but it doesn't "eliminate" the need for terminations, you are simply lucky it works without them.
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Rob Spence
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Rob Spence

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Re: DMX cables
« Reply #17 on: November 12, 2010, 07:05:41 pm »

Micky Basiliere wrote on Thu, 11 November 2010 21:47

Shane Presley wrote on Thu, 11 November 2010 15:41

The best difference it makes for me is the lighting patch cables are not taken for audio use, and visa versa... I ordered all my DMX in purple, so it's VERY distinct.  This makes trouble shooting, or patching a lot easier than following 2 black mic cables, one audio and one dmx.... As others have said it's a minimal cost difference to use the "correct stuff". Also I've found using a termintor is not needed unless it's needed - if that makes sense... If your fixtures are behaving without termination then don't bother. If they are erratic, then terminate.  

I'll also throw one out to the "no dmx on audio lines" guys... 9 times out of 10, I run the lighting sends, up my audio snake (250ft), before it hits the opto splitter.  Yes the 10th time, it makes noise on the audio, but for the most part it works like a charm... when it doesn't I run 2 x 100ft dmx lines...but that's rare...


I do the opposite...From FOH,from opto splitter(6 sends) out through 150' lighting ONLY snake to stage...NO TERMINATORS(they only cause problems!) I would not recommend sending DMX through an audio snake??? just my 2 cents... Smile

I submit that correct termination of the DMX line would not cause problems. Explain please.

I don't recommend sending DMX down audio cables either but I do it when I have to knowing I am taking some amount of risk.
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Rob Spence
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Rob Timmerman

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Re: DMX cables
« Reply #18 on: November 12, 2010, 07:32:18 pm »

Rob Spence wrote on Fri, 12 November 2010 18:58

Rob Timmerman wrote on Thu, 11 November 2010 20:11

Rob Spence wrote on Thu, 11 November 2010 00:10

Thomas Bishop wrote on Wed, 10 November 2010 09:55

... and 3-pin DMX is perfectly acceptable for microphone cable.  I have 1000' spool of DMX cable on order to replace all my mic cables, and it's only pennies more than mic cable.

But DMX cable may not be ok for audio.

Different cable for different uses.

Audio cable works ok for DMX use for short runs. Long runs or reliability should use DMX cable.



Why would DMX cable not be ok for audio?

Well, for one thing it is the wrong impedance. Why do you think there are multiple kinds of cable?
Heck, my main power feeder has twisted conductors but that doesn't make it ok for mic cable.
So, shielded twisted pair for mic cables is a different impedance than that for DMX because DMX is a digital signal and audio is analog.

An electric circuit such as the input of a mixer is made up of 3 main components. There is the mic, the cable, and the mixer preamp. Together they make a circuit that takes sound waves, generates electricity, transmits it over the wires and into the mixer. For it to work right (meaning get the audio into the mixer without distorting it), all the impedances should be correct. Same goes for other kinds of circuits like TV antenna or WIFI antenna.



So I take it you wouldn't mix'n'match Canare L4-E6s (Z=44 ohms), Belden 8412 (Z=67 ohms), or snake cables (Z ranging from 40 through 70 ohms depending on the cable) in the same run for a mic cable?  (Connecting 8412 to the StarQuad is the same amount of mismatch as connecting the 8412 to a 110 ohm DMX cable).


The reality is that cable impedance only really becomes important once the cable is long enough that it needs to be treated as a transmission line (~1/10 wavelength).  For audio frequencies, this is around 1km, or rather longer than we typically encounter.  For DMX runs, this 1/10 wavelength is around 150', or well within what may be encountered in typical environments.
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Rob Spence

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Re: DMX cables
« Reply #19 on: November 13, 2010, 11:56:40 am »

Rob Timmerman wrote on Fri, 12 November 2010 19:32

Rob Spence wrote on Fri, 12 November 2010 18:58

Rob Timmerman wrote on Thu, 11 November 2010 20:11

Rob Spence wrote on Thu, 11 November 2010 00:10

Thomas Bishop wrote on Wed, 10 November 2010 09:55

... and 3-pin DMX is perfectly acceptable for microphone cable.  I have 1000' spool of DMX cable on order to replace all my mic cables, and it's only pennies more than mic cable.

But DMX cable may not be ok for audio.

Different cable for different uses.

Audio cable works ok for DMX use for short runs. Long runs or reliability should use DMX cable.



Why would DMX cable not be ok for audio?

Well, for one thing it is the wrong impedance. Why do you think there are multiple kinds of cable?
Heck, my main power feeder has twisted conductors but that doesn't make it ok for mic cable.
So, shielded twisted pair for mic cables is a different impedance than that for DMX because DMX is a digital signal and audio is analog.

An electric circuit such as the input of a mixer is made up of 3 main components. There is the mic, the cable, and the mixer preamp. Together they make a circuit that takes sound waves, generates electricity, transmits it over the wires and into the mixer. For it to work right (meaning get the audio into the mixer without distorting it), all the impedances should be correct. Same goes for other kinds of circuits like TV antenna or WIFI antenna.



So I take it you wouldn't mix'n'match Canare L4-E6s (Z=44 ohms), Belden 8412 (Z=67 ohms), or snake cables (Z ranging from 40 through 70 ohms depending on the cable) in the same run for a mic cable?  (Connecting 8412 to the StarQuad is the same amount of mismatch as connecting the 8412 to a 110 ohm DMX cable).


The reality is that cable impedance only really becomes important once the cable is long enough that it needs to be treated as a transmission line (~1/10 wavelength).  For audio frequencies, this is around 1km, or rather longer than we typically encounter.  For DMX runs, this 1/10 wavelength is around 150', or well within what may be encountered in typical environments.

For Audio, I would not be bothered by the mis matches as I am unlikely to hear the resulting distortion.
For DMX, the distortion may result in bright lights pointing where they should not.
Your call.
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Rob Spence
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