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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Lighting Forum => Topic started by: Lyle Williams on September 27, 2015, 06:06:52 pm

Title: DMX over mic cables
Post by: Lyle Williams on September 27, 2015, 06:06:52 pm

I know that you are "meant" to use different DMX-specific cable, but using XLR mic leads is pretty convenient.

There have been suggestions that range is reduced when using mic cables.  I don't doubt that, but a question remained for me: how far can I go on mic leads?

I plugged in 400m of mic lead between my controlling PC and the DMX fixtures.  It still worked fine.

Title: Re: DMX over mic cables
Post by: Rob Spence on September 27, 2015, 07:10:00 pm
I know that you are "meant" to use different DMX-specific cable, but using XLR mic leads is pretty convenient.

There have been suggestions that range is reduced when using mic cables.  I don't doubt that, but a question remained for me: how far can I go on mic leads?

I plugged in 400m of mic lead between my controlling PC and the DMX fixtures.  It still worked fine.

Audio cable has an impedance to match audio gear. DMX is data like AES is and as such needs cable with the right impedance.

When a connection is made between 2 different impedance cables (audio cable to DMX fixture), it causes reflections (think of it like noise) which when severe will disrupt the data and cause errors.

 So, when you have a bunch of fixtures connected with mic cables, each connection adds a little more noise. At some point your data will be corrupted enough and you will get strange results.

Lots of people cheat and use mic cables. As long as it is working, they are happy. The first show that is ruined because your lights won't behave might cost you a customer or at least frustration, embarrassment and a ding to your reputation.

If the cost of the right cables to do the job is a problem for you, I would think you have bigger problems or at least some out of order priorities.

Don't forget to put terminators on the last fixture in the chain.


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Title: Re: DMX over mic cables
Post by: Lyle Williams on September 27, 2015, 09:55:01 pm

I guess my point is that if works at 400m, then there is little to be scared about with 40m of cable.
Title: Re: DMX over mic cables
Post by: Jamin Lynch on September 27, 2015, 10:22:32 pm
I guess my point is that if works at 400m, then there is little to be scared about with 40m of cable.

Or you can go wireless DMX
Title: Re: DMX over mic cables
Post by: Tom Bourke on September 27, 2015, 10:51:12 pm
I guess my point is that if works at 400m, then there is little to be scared about with 40m of cable.
It will work great, till it doesn't.  Those reflections can happen at any change in impedance, for example mixing cable types.  Most instruments just have the in and out tied together.  This means that ALL cables in the path count. Join 4 lights and a controller together with 100ft cables and you have 400 ft of cable with 3 taps and 2 ends.  Lets say 16 lights with 100 ft to FOH and 100 ft cable tree to tree with 4 per tree and a mix of random mic cables in each tree.  Now you have all kinds of fun. Every one of those joints or ends can create reflections.  Changing the order of the cables can change where and how the reflections are happening.  The system will get wonky when those reflections start to interfere with the data stream.  It may be just one of hundreds of possible combinations that can cause problems.

Point being that yes mic cables will work just fine, MOST of the time but not ALL of the time.
Title: Re: DMX over mic cables
Post by: Rob Spence on September 27, 2015, 11:16:18 pm
I guess my point is that if works at 400m, then there is little to be scared about with 40m of cable.

Not many impedance changes here. A set of 20' cables to a bunch of fixtures might not.


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Title: Re: DMX over mic cables
Post by: TJ (Tom) Cornish on September 28, 2015, 10:36:47 pm
Or you can go wireless DMX
For reliability, I would take DMX on mic cable 100/100 times over wireless DMX.
Title: Re: DMX over mic cables
Post by: Jamin Lynch on September 28, 2015, 11:01:11 pm
For reliability, I would take DMX on mic cable 100/100 times over wireless DMX.

I've been running wireless DMX for a while now with no issues. I love it. Beats the hell out of running cables.
Title: Re: DMX over mic cables
Post by: Scott Holtzman on September 29, 2015, 02:09:53 am
I've been running wireless DMX for a while now with no issues. I love it. Beats the hell out of running cables.
Jamin we have been on the same page lately.  I picked up a box of oem dmx wireless boards and have been installing them in about 15% of my PAR'S and all my movers.  Can't wait until I am done.

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Title: Re: DMX over mic cables
Post by: Jamin Lynch on September 29, 2015, 07:17:45 am
Jamin we have been on the same page lately.  I picked up a box of oem dmx wireless boards and have been installing them in about 15% of my PAR'S and all my movers.  Can't wait until I am done.

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I've been using the ADJ WyFly transceivers for about a year now. Mounted one on each light bar. Just run power to each light bar and go. I also have the wireless controller. No cable from FOH.

I guess it depends on your situation, but for me it has worked well.
Title: Re: DMX over mic cables
Post by: Keith Broughton on September 29, 2015, 07:33:31 am
I guess my point is that if works at 400m, then there is little to be scared about with 40m of cable.
OK....so if it works, what is the question?
Title: Re: DMX over mic cables
Post by: Lyle Williams on September 29, 2015, 12:49:18 pm
OK....so if it works, what is the question?

Just sharing my findings so one day google can help someone out...
Title: Re: DMX over mic cables
Post by: Scott Holtzman on September 29, 2015, 01:15:12 pm
Just sharing my findings so one day google can help someone out...

It doesn't help.  Just because it worked for you it gives a false sense of security.  We don't know what type of MIC cable you were using nor the inductive nature of your environment.

These threads are annoying and destructive because the OP is always looking for someone to justify doing something wrong or marginal.   The answer is you are giving up safety margin.  You want to take a chance at your lights going out on a critical show and the loss of business and reputation.

If you are doing middle school dances and this isn't an issue then I guess it's useful information.  The assumption here is everyone is a working professional and in my mind professionals don't use the wrong cable to save a few bucks.

BTW I speak from experience, I have made these mistakes, choose the easier softer path.  I ended up tossing out or giving away the garbage and only use the good stuff I should have bought in the beginning. 



Title: Re: DMX over mic cables
Post by: Nate Armstrong on September 30, 2015, 05:27:51 pm
I make all my cables including Microphone cables  with 110 ohm dmx cable and Neutrik connectors.
Then I can use any of my XLR cable for mic or dmx.
Title: Re: DMX over mic cables
Post by: David Buckley on September 30, 2015, 06:36:10 pm
It will work great, till it doesn't.

This.

If the show doesn't really matter, and the risk of failure is acceptable, then go ahead, save a buck or two, and use mic cables.

If you are charging money, or claim to be "professional", well, then, that's different.

Title: Re: DMX over mic cables
Post by: Lyle Williams on October 01, 2015, 12:15:37 pm
It doesn't help.  Just because it worked for you it gives a false sense of security.  We don't know what type of MIC cable you were using nor the inductive nature of your environment.

These threads are annoying and destructive because the OP is always looking for someone to justify doing something wrong or marginal.   The answer is you are giving up safety margin.  You want to take a chance at your lights going out on a critical show and the loss of business and reputation.

If you are doing middle school dances and this isn't an issue then I guess it's useful information.  The assumption here is everyone is a working professional and in my mind professionals don't use the wrong cable to save a few bucks.

BTW I speak from experience, I have made these mistakes, choose the easier softer path.  I ended up tossing out or giving away the garbage and only use the good stuff I should have bought in the beginning. 





I did start the post by saying that proper DMX cables are the proper solution.

Note that 3-pin DMX only exists to allow people to use mic cables.  3-pin DMX isn't a "pro" solution, but it is a very popular one.

DMX is RS485 at 250kbps.  Carrying this over the twisted pair we're willing to trust our precious audio to isn't electrically very challenging.

If fears about reflections keep you up at night, just use a lower value terminating resistor.  :-)
Title: Re: DMX over mic cables
Post by: Scott Holtzman on October 02, 2015, 02:36:24 am
I did start the post by saying that proper DMX cables are the proper solution.

Note that 3-pin DMX only exists to allow people to use mic cables.  3-pin DMX isn't a "pro" solution, but it is a very popular one.

DMX is RS485 at 250kbps.  Carrying this over the twisted pair we're willing to trust our precious audio to isn't electrically very challenging.

If fears about reflections keep you up at night, just use a lower value terminating resistor.  :-)
I would hate to be called out for having the wrong cables.  I was speaking more on principal that validation from strangers in a forum under the auspices of soliciting an opinion is weak.  Personally I am so lazy and no by will pay extra for lighting I use wireless.  if it screws up the fixtures go in sound activated mode.  My light show is a bonus.

Those kind of decisions and risk reward analysis require more understanding of the situation than just technical.

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Title: Re: DMX over mic cables
Post by: Jordan Wolf on October 02, 2015, 09:16:38 am
Note that 3-pin DMX only exists to allow people to use mic cables.  3-pin DMX isn't a "pro" solution, but it is a very popular one.
I was under the impression that certain manufacturers had used 3-pin XLR for a more "proprietary" connection before 5-pin was accepted industry-wide.

I don't think you would find any [reputable] manufacturer that recommends or suggests using standard microphone cables for control interconnect.
Title: Re: DMX over mic cables
Post by: Tom Burgess on October 02, 2015, 10:10:11 am

...Note that 3-pin DMX only exists to allow people to use mic cables...
Now there's an interesting little tidbit that I've never seen put forth.  Is there an actual source for this?
Title: Re: DMX over mic cables
Post by: Chris Jensen on October 02, 2015, 02:34:32 pm
I did start the post by saying that proper DMX cables are the proper solution.

Note that 3-pin DMX only exists to allow people to use mic cables.  3-pin DMX isn't a "pro" solution, but it is a very popular one.

DMX is RS485 at 250kbps.  Carrying this over the twisted pair we're willing to trust our precious audio to isn't electrically very challenging.

If fears about reflections keep you up at night, just use a lower value terminating resistor.  :-)

I always thought that the USITT DMX-512A standard called for 5 wires.  Even though 2 of those connections are reserved they are part of the standard. 

After reading the PLASA ANSI document it seems that any non 5-pin XLR type connectors are only allowed in very limited cases.   It does not specially call out 3-pin as being disallowed, but 3-pin is obviously not 5-pin.

See section 7 - http://tsp.plasa.org/tsp/documents/docs/E1-11_2008R2013.pdf

I have always wondered if MPX has historically affected DMX and its perception in anyway.  I wonder if any of the manufacturers that started using 3-pin way back when decided not to seek using the DMX standard.  The ANSI document did clearly state how to note the use of DMX in the manual and on the gear.  Do any of the 3-pin instruments actually list it as the official DMX standard, or are they using the protocol without actually calling it official DMX-512A.  See section 7 for this also.

If anyone has any other info please add on and correct me!
Title: Re: DMX over mic cables
Post by: Lyle Williams on October 02, 2015, 05:33:42 pm


So why are so many of the fixtures and desks built deliberately to be non-compliant with the standard?  Because people want to use their existing mic cables, and because - up to a point - these mic cables work.

My test was just about gaining an intuitive feel for where the limit was for DMX on mic cable. 

Title: Re: DMX over mic cables
Post by: Rob Spence on October 02, 2015, 10:19:45 pm

So why are so many of the fixtures and desks built deliberately to be non-compliant with the standard?  Because people want to use their existing mic cables, and because - up to a point - these mic cables work.

My test was just about gaining an intuitive feel for where the limit was for DMX on mic cable.

I would say they can use the same connectors to build or repair the cables.


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Title: Re: DMX over mic cables
Post by: Scott Wagner on October 03, 2015, 01:10:56 am
I would say they can use the same connectors to build or repair the cables.
Ding! Ding! We have a winner.
Title: Re: DMX over mic cables
Post by: Scott Hofmann on October 03, 2015, 09:01:43 am

So why are so many of the fixtures and desks built deliberately to be non-compliant with the standard?  Because people want to use their existing mic cables, and because - up to a point - these mic cables work.

My test was just about gaining an intuitive feel for where the limit was for DMX on mic cable.

OK, I can't stay silent any more.
If you want something to validate your opinion, here's a rant on DMX versus mic cable from the Cheaplights.com website. Consider the source.

A Simple Guide To DMX CABLES...
SECTION 1: INTRODUCTION
Let's talk about DMX cables... I recently received and email from a blog monitor that said... "There are MICROPHONE cables and there are DMX cables and one can NOT be used for the other". That's a very strong statement. Very "Black and White". Unfortunately, it's also very untrue. That statement would be like saying that Chevy's are for taking your kids to school and Ferrari's are for racing and one can not be used for the other. I have seen many people race Chevy's successfully and I have also seen a few Ferrari's in the school pick up lanes. I don't know exactly why people make those black and white statements about DMX cables. Perhaps they merely lack real world experience in the field.
SECTION 2: REAL WORLD EXPERIENCE
If they had real world experience, they would know that there were companies like NSI making digitally controlled lighting boards and dimmer packs with signals carried thru 3 pin XLR cables long before the term DMX was ever heard of here in America. (NSI calls their proprietary signal MICROPLEX and they still use it today). What do you think those digital signals were carried thru back before the late 90's when DMX was introduced to the commercial market here in America? MICROPHONE CABLES. That's all we had back then, that's what was used and that's what worked for years.
SECTION 3: IT's JUST A NAME
Perhaps some cables marked "DMX Cable" might perform better than some cables marked "MICROPHONE Cable", but it can also be proven that some mid to high grade MIC cables work better than some DMX cables and if you and your audience can't tell the difference, who cares? What does matter is which pins the wires are connected to on the 3 pin XLR plug. At High Energy Lighting (CheapLights.com), we currently buy "MIC" cables and "DMX" cables from over 22 different suppliers. Regardless of how they are marked, we test samples from each different "MIC" and "DMX" cable model to make sure they work in a DMX chain before we ever offer them to our customers.
SECTION 4: THE FACTS
Here's an interesting fact... In the ten to fifteen years that we have been selling cables for transmitting digital signals for light processors, we have never had any cables returned by customers saying they didn't work as a DMX cable, unless the cable actually had a physical defect, such as a wire not connected to the plug or a cut in the wire. That's a great statement to be able to make!

 Here's a few more interesting facts... 1. "DMX" was created in 1986, but not widely used or known. At that time, the popular method for transmitting signal to dimmer packs was zero to ten volts. 2. "DMX" was revised in a major way and started gaining recognition in 1990. (But not in America). 3. The first DMX lighting controllers were displayed at the American LDI Lighting convention in 1999 by LitePuter. 4. "DMX" was introduced as the "Standard" digital signal for the World Wide lighting industry in 2000.

If you feel validated now, can we stop talking about this because obviously no one is going to change your mind.
Title: Re: DMX over mic cables
Post by: RyanWilliams on October 03, 2015, 12:57:27 pm
OK, I can't stay silent any more.
If you want something to validate your opinion, here's a rant on DMX versus mic cable from the Cheaplights.com website. Consider the source.

A Simple Guide To DMX CABLES...
SECTION 1: INTRODUCTION
Let's talk about DMX cables... I recently received and email from a blog monitor that said... "There are MICROPHONE cables and there are DMX cables and one can NOT be used for the other". That's a very strong statement. Very "Black and White". Unfortunately, it's also very untrue. That statement would be like saying that Chevy's are for taking your kids to school and Ferrari's are for racing and one can not be used for the other. I have seen many people race Chevy's successfully and I have also seen a few Ferrari's in the school pick up lanes. I don't know exactly why people make those black and white statements about DMX cables. Perhaps they merely lack real world experience in the field.
SECTION 2: REAL WORLD EXPERIENCE
If they had real world experience, they would know that there were companies like NSI making digitally controlled lighting boards and dimmer packs with signals carried thru 3 pin XLR cables long before the term DMX was ever heard of here in America. (NSI calls their proprietary signal MICROPLEX and they still use it today). What do you think those digital signals were carried thru back before the late 90's when DMX was introduced to the commercial market here in America? MICROPHONE CABLES. That's all we had back then, that's what was used and that's what worked for years.
SECTION 3: IT's JUST A NAME
Perhaps some cables marked "DMX Cable" might perform better than some cables marked "MICROPHONE Cable", but it can also be proven that some mid to high grade MIC cables work better than some DMX cables and if you and your audience can't tell the difference, who cares? What does matter is which pins the wires are connected to on the 3 pin XLR plug. At High Energy Lighting (CheapLights.com), we currently buy "MIC" cables and "DMX" cables from over 22 different suppliers. Regardless of how they are marked, we test samples from each different "MIC" and "DMX" cable model to make sure they work in a DMX chain before we ever offer them to our customers.
SECTION 4: THE FACTS
Here's an interesting fact... In the ten to fifteen years that we have been selling cables for transmitting digital signals for light processors, we have never had any cables returned by customers saying they didn't work as a DMX cable, unless the cable actually had a physical defect, such as a wire not connected to the plug or a cut in the wire. That's a great statement to be able to make!

 Here's a few more interesting facts... 1. "DMX" was created in 1986, but not widely used or known. At that time, the popular method for transmitting signal to dimmer packs was zero to ten volts. 2. "DMX" was revised in a major way and started gaining recognition in 1990. (But not in America). 3. The first DMX lighting controllers were displayed at the American LDI Lighting convention in 1999 by LitePuter. 4. "DMX" was introduced as the "Standard" digital signal for the World Wide lighting industry in 2000.

If you feel validated now, can we stop talking about this because obviously no one is going to change your mind.

This “Guide” is junk.
Section 1
While yes you can, and we all have run DMX through a mic cable it isn’t a best practice.  DMX is RS-485 serial data.  RS-485 is balanced like audio and by design is very robust.  It was originally designed for process control in factories.  It is specified to go over twisted pair.  Microphone cables may or may not have the correct twist.  The fact that it works is a testament to it’s robustness, not permission to do so.  Like I mentioned, we have all done it…We have all had a dimmer or intelligent light that has gone “wonky” or ghosted.  Ever wonder why?
Section 2  Real Real world experience
Microplex is not a digital signal.  It is a multiplexed 0 to 10V analog signal.  It’s not even a balanced signal, and it was designed to be able to use microphone cables.  DMX by the USITT specification is supposed to be on 5 pin cables not 3 pin cables.  When the low end companies like American DJ, Chauvet etc…  got involved they started using 3 pin cables and calling it DMX-512 which is a clear violation of the USITT DMX-512 standard.  A lot of the reason the USITT standard was for 5 pin cables was to prevent people from doing exactly what you are doing and causing poor performance resulting in people thinking the protocol was junk.  Anyone who works in Theatre is accustomed to seeing DMX on the 5 pin cables.  Most of us have adaptors in our bags.  The 3 pin variance is so bad that within martin’s line they have some devices that reverse the polarity of the pins requiring one of the ends to have pins 2 and 3 swapped.
DMX is supposed to be a balanced twisted pair 120Ohm cable.  A much closer cable than microphone is Ethernet which is 100Ohm twisted pair.  It’s much cheaper and can run 4 DMX universes in one cable…Although I wouldn’t.
Section 3 It’s just a name…
Is SOOW cable just a name?  Why don’t you buy some massive THHN electrical cables throw some camloks on them and drag them around and hook up your feeders with them.  How about just before the show opens, have the local electrical inspector drop by and see if you get shut down.  Why would you buy cables from 22 different manufacturers?  Have you not found one that works well yet?
Section 4 The facts
Of course you haven’t had the cables returned.  Who is going to ship a cable back that works in the sound system back?  They just absorbed that cable into the sound system, and called a competent supplier and ordered real DMX cables from there.  You never heard from that customer again.
Interesting Facts: - Checked
1.    Partly true
a.   The DMX standard was released by USITT in 1986.  However, it became popular within a few years.  It was installed in the High School Theatre that I was going to high school at in 1990.
b.   The popular method at the time for any large show was AMX-192 with some other variants like Microplex.
2.   Completely False - The boards installed at out high school in 1990 were made by Colortran.  ETC and everyone else was doing DMX at the same time too.

The bottom line here.  Remember the rule from shop class “Use the right tool for the job”  If you have purchased $100K worth of intelligent lights are you going to cheap out on a mic cable or use the correct thing?  If you are using Chinese semi-pro low end gear like American DJ, Chauvet and the like you don’t have enough skin in the game to care if you are doing things right, and you won’t know if that device malfunction was the low end device or the wrong cable. If you have a reputation and a contract riding on it you do things correctly to specification, and it works.  Are you a pro or a semi-pro?
Title: Re: DMX over mic cables
Post by: Keith Broughton on October 03, 2015, 03:28:11 pm
Quote
Are you a pro or a semi-pro?
And that my friends is the real question here.
Title: Re: DMX over mic cables
Post by: Lyle Williams on October 03, 2015, 05:49:36 pm
And that my friends is the real question here.

From the first post, there was no suggestion that mic cable was the "right" solution, just one that seemed to work.

Looking at the signal on a cro after 400m, the signal still looks great.  Pull the terminating resistor off the end and it looks dreadful (but it STILL works!)

Anyone who has brought a roll of gaff tape to a show has indicated some level of willingness to improvise and get the job done.  I was just trying to put some perspective on short on-stage DMX runs on mic cable.  Not the "right thing", but not nearly as dodgey as the mythology suggests.
Title: Re: DMX over mic cables
Post by: Lyle Williams on October 03, 2015, 06:29:40 pm
None of this necessarily makes DMX-on-Mic an acceptable solution for your customers. 

A solution customers have confidence in needs to both work, and also not violate any techno-religious, artistic, etc opinions they hold.  Across a whole spectrum of cutomers.
Title: Re: DMX over mic cables
Post by: Keith Broughton on October 04, 2015, 07:11:45 am
And that my friends is the real question here.
Let me expand a bit on this point.
If you are a professional company in the biz, you are likely to use the cable that is specified for DMX applications as you want to maintain your reputation to your customers. You also want to make sure the top tier equipment you invested in will work properly.
If you are semi-pro ( that's not a negative thing) you have less to loose and can get away with using mic cable on the cheap "off shore" fixtures and , for the most part, it will work and your customers will be happy.
So, are you pro or semi pro?
 I would say that the people who have responded with the "use the right cable" have been doing this for a long time and have bite marks on their ass from times they thought they could get away with the "so far it has worked" approach.
Title: Re: DMX over mic cables
Post by: Scott Holtzman on October 04, 2015, 08:33:34 am
I think a good take away is if you are going to take the risk use a terminator.

Also as I don't like the term semi pro,  how about pro serving undeserved low end of market?

The funny thing is that cables are such a small amount of the expense get the right ones. 

I learned the hard way and bought cheap dmx cables.  while the impedance may have been right the quality of construction caused more failures than using mic cable ever would.





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Title: Re: DMX over mic cables
Post by: Lyle Williams on October 04, 2015, 10:10:05 am
If you aren't using a terminator you are committing a sin an order of magnitude worse than using mic cable.  :-)

Title: Re: DMX over mic cables
Post by: Rob Spence on October 04, 2015, 12:08:47 pm
I think a good take away is if you are going to take the risk use a terminator.

Also as I don't like the term semi pro,  how about pro serving undeserved low end of market?

The funny thing is that cables are such a small amount of the expense get the right ones. 

I learned the hard way and bought cheap dmx cables.  while the impedance may have been right the quality of construction caused more failures than using mic cable ever would.





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Scott, I presume you meant under served?

I bought a couple of spools of DMX cable, added Neutrik connectors. And use an opti splitter with terminators.


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Title: Re: DMX over mic cables
Post by: Scott Holtzman on October 04, 2015, 07:19:33 pm
Scott, I presume you meant under served?

I bought a couple of spools of DMX cable, added Neutrik connectors. And use an opti splitter with terminators.


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Rob, yes under served.    I also used an active splitter before I went wireless

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