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Author Topic: Power/Mic Line Separation  (Read 8160 times)

Andre Vare

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Power/Mic Line Separation
« on: April 21, 2011, 03:31:05 pm »

I am involved in several forums about recording studio design.  A question that pops up semi-regugarly is how close can mic lines be to power lines.  I constantly give th example of outdoor concerts where the stage to FOH run has mic, power, line level, DMX and others in close proximity to each other, up to being taped together. 

In order to simplify answering, I included a poll type response.  Addtional comments are more than welcome.

When doing stage to FOH cable runs how close do you have the audio snake to the power lines?

T Taped together
0 0-2"
2 2-4"
4 4-8"
8 8-16"
M More than 16"
S Separate runs

Thanks.

Andre
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John Roberts {JR}

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Re: Power/Mic Line Separation
« Reply #1 on: April 21, 2011, 03:39:31 pm »

This is not a simple single distance spacing answer but depends on
A- the quality of wire used (uniformity of wrap and shielding)
B- angle of attack (parallel vs. normal, vs. other
C- the quality of the preamps (CMRR)
D- nature of power lines (120 vs 240, clean vs dirty, dimmers etc).
E- noise floor requirement of application.

JR


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Chris Hindle

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Re: Power/Mic Line Separation
« Reply #2 on: April 21, 2011, 04:43:24 pm »

Under 150 feet, T
Over 200 feet, S
If over 150 or so, I try to get mic and drive lines on one side, and power on the other. It doesn't always work out that way though.

Chris.
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Justin Bartlett

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Re: Power/Mic Line Separation
« Reply #3 on: April 21, 2011, 05:00:18 pm »

I am involved in several forums about recording studio design.  A question that pops up semi-regugarly is how close can mic lines be to power lines.  I constantly give th example of outdoor concerts where the stage to FOH run has mic, power, line level, DMX and others in close proximity to each other, up to being taped together. 

In order to simplify answering, I included a poll type response.  Addtional comments are more than welcome.

When doing stage to FOH cable runs how close do you have the audio snake to the power lines?

T Taped together
0 0-2"
2 2-4"
4 4-8"
8 8-16"
M More than 16"
S Separate runs

Thanks.

Andre

John Roberts makes a good point, especially in that noise floor requirements may be different between a live event and a recording studio.
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Tom Young

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Re: Power/Mic Line Separation
« Reply #4 on: April 21, 2011, 05:53:25 pm »

John Roberts makes a good point, especially in that noise floor requirements may be different between a live event and a recording studio.

They ARE very different.

Ambient noise at a live show is much higher than that in even a fairly amateurishly "designed" home studio. This noise will mask much/all of the system noise that would be very evident in a recording studio.

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Bennett Prescott

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Re: Power/Mic Line Separation
« Reply #5 on: April 21, 2011, 06:19:46 pm »

Live audio is not recording studio audio. Everyone tapes their FOH runs together, power and signal, line level or mic level.
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Andre Vare

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Re: Power/Mic Line Separation
« Reply #6 on: April 21, 2011, 07:06:25 pm »

Thanks everyone so far.  The differences between professional live sound and amateur recording are well known.  This is a straw poll and YMMV, or perhaps more accurately the results are an average.  Like an average presenting one aspect of powering in isolation.  Or maybe the average human being, with one ovary and one testicle.   :o

Beyond what John wrote the significant factor for EMI is current, not voltage. 

Of course if anything live power is going to be dirtier.

Background noise is significant in live sound.  On that point, and this is not a rhetorical question, how often have you made board recordings, either mix or isolated inputs and found unacceptable tracks due to power line related or suspected noise?  Some Midas consoles even have separate level controls on direct outs for recording.

As I wrote in the original post, additional comments are more than welcome.

An extra thanks to the people who posted and did answer the straw poll question in their responses.

Andre
« Last Edit: April 21, 2011, 07:08:49 pm by Andre Vare »
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Randall Hyde

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Re: Power/Mic Line Separation
« Reply #7 on: April 21, 2011, 07:25:25 pm »



When doing stage to FOH cable runs how close do you have the audio snake to the power lines?

T Taped together
0 0-2"
2 2-4"
4 4-8"
8 8-16"
M More than 16"
S Separate runs

Thanks.

Andre

Switched to digital. Now I run power lines alongside Cat 6 :)

Seriously, though, I'm looking at one of the new Whirlwind snakes that run two CAT6 lines along with 6 multicore pairs (for talkback, CD players, etc., at FOH). I'd probably set that in the 0-2 range in the list above as I'd just drop the two cables in the same gutter that leads to FOH (most of my shows are street festivals).  Never really had a problem with noise running a 12GA power cord alongside a snake to FOH in my old analog system. 95% of the time, any noise in the system was from dimmer packs (dirty power) or the musician's gear. The other 5% of the time it was ground loops.
cheers,
Randy Hyde
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Mac Kerr

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Re: Power/Mic Line Separation
« Reply #8 on: April 21, 2011, 08:26:54 pm »

I am involved in several forums about recording studio design.  A question that pops up semi-regugarly is how close can mic lines be to power lines.  I constantly give th example of outdoor concerts where the stage to FOH run has mic, power, line level, DMX and others in close proximity to each other, up to being taped together. 

Are you asking about the recording studio scenario, or the live event scenario? The answers are different for each environment. Live sound with an audience, all signal levels in separate cables taped together is fine. In a studio, separate conduit for each signal level, a couple of inches apart.

Mac
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James Boutilier

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Re: Power/Mic Line Separation
« Reply #9 on: April 22, 2011, 10:37:35 am »

In a studio, separate conduit for each signal level, a couple of inches apart.

Mac

+1.  In the design of modern performing arts facilities, the infrastructure is frequently used for both live sound and recording.  Different signal levels are run in separate metallic conduit and separated by several inches.
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Brad Weber

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Re: Power/Mic Line Separation
« Reply #10 on: April 22, 2011, 12:48:33 pm »

Jim Brown, Pat Brown and Dale Shirk have all performed testing of various cable types and separations to different EMI sources including a parallel power run and a simulated localized higher energy EMI source (I blieve that Dale used a bulk tape eraser).  They found that the physical separation is definitely a significant factor but as already noted, so were the cable and even the devices to which it connects.  I look at it this way, if you could insure the the interfering source affects each conductor of a balanced circuit equally and you can properly address SCIN and Pin 1 issues, then a high quality differential input would cancel whatever noise is induced.  Those factors are cable and device dependent and the further they deviate from the ideal, the more you have to depend on physical separation.  Add in the aspect of what is an acceptable result varying by application and there unfortunately is no broadly encompassing answer.
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Justice C. Bigler

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Re: Power/Mic Line Separation
« Reply #11 on: April 22, 2011, 05:47:20 pm »

I live sound, particularly in touring shows, pretty much everything is taped together, or in groups going to the same places. Often times you have no choice but to run power feeder and cross stage bundles along the same path. Separate them if you can, but sometimes it is what it is. It you are using well made cables and the shields are all intact, you should have only minimal problems. Other times if there is a bad problem, you may have to carry an extra 150 foot mult or feeder bundle to reroute things.
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Andre Vare

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Re: Power/Mic Line Separation
« Reply #12 on: April 23, 2011, 10:57:22 am »

Thanks everyone so far.  Most have have gone where it is irrelevant to my question.  Let me do the introduction again.

I am amongst other hats, a studio designer.  I am involved in a discussion on a studio design forum where John Brandt (another studio designer) and I are trying to explain "zero loop area" design.  Several people have written that power and signal lines can not be adjacent to each other.  I have referenced work by Dan Brown on line separation requirements in conduit and given the example of power/signal lines together in live sound.  To help get across the point of what works, how much do you separate the power and signal lines when doing outdoor events?

Andre
« Last Edit: April 23, 2011, 11:05:28 am by Andre Vare »
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Art Welter

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Re: Power/Mic Line Separation
« Reply #13 on: April 23, 2011, 11:24:14 am »

Thanks everyone so far.  Most have have gone where it is irrelevant to my question.  Let me do the introduction again.

I am amongst other hats, a studio designer.  I am involved in a discussion on a studio design forum where John Brandt (another studio designer) and I are trying to explain "zero loop area" design.  Several people have written that power and signal lines can not be adjacent to each other.  I have referenced work by Dan Brown on line separation requirements in conduit and given the example of power/signal lines together in live sound.  To help get across the point of what works, how much do you separate the power and signal lines when doing outdoor events?

Andre
I have taped the AC to the snake since 1974, my first snake was 50 feet, later snakes were 250 feet.
I have audio tapes and CDs of shows going back to that same time period, any audible 60 Hz and harmonic noise is always from the stage (guitar, bass, keys) amps.

The only time that the induced noise of the AC line has ever been the slightest problem has been on shows using low gain lavaliere microphones worn on the chest by soft talking individuals. In that case, with the input pre amps wide open, some AC hum harmonics were noticeable, but that noise was swamped by dimmer noise.

At the level of input given by any usual pop performance, any 60 cycle induced noise from taping the AC to the snake is so far below ambient noise as to be a total non issue if decent wire and consoles are used.

Which is why I have never seen a touring company run separate AC and snake runs.
Anyway, that would be well over 200 votes for "T", and none for any of the rest in my experience with touring "rock and roll" productions.
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Mac Kerr

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Re: Power/Mic Line Separation
« Reply #14 on: April 23, 2011, 11:34:53 am »

Thanks everyone so far.  Most have have gone where it is irrelevant to my question.  Let me do the introduction again.

I am amongst other hats, a studio designer.  I am involved in a discussion on a studio design forum where John Brandt (another studio designer) and I are trying to explain "zero loop area" design.  Several people have written that power and signal lines can not be adjacent to each other.  I have referenced work by Dan Brown on line separation requirements in conduit and given the example of power/signal lines together in live sound.  To help get across the point of what works, how much do you separate the power and signal lines when doing outdoor events?

Andre

Your question is still a little unclear. Most of your message talks about studios, but then seems to swerve to live concert sound. If you are inquiring about how to deal with power and signal lines in an outdoor live concert situation, it is fine to bundle power with the mic multi and the line level return snake. If you have to run mic level signals with high power, like hundreds of amps of worth of feeder cable you should try to get as much separation as you can. Unlike a studio installation you will often have little control over where cable is able to be run. With the exception of running with alongside feeder cable you should be fine.

Mac
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Andre Vare

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Re: Power/Mic Line Separation
« Reply #15 on: April 23, 2011, 12:02:10 pm »

Your question is still a little unclear. Most of your message talks about studios, but then seems to swerve to live concert sound. If you are inquiring about how to deal with power and signal lines in an outdoor live concert situation, it is fine to bundle power with the mic multi and the line level return snake. If you have to run mic level signals with high power, like hundreds of amps of worth of feeder cable you should try to get as much separation as you can. Unlike a studio installation you will often have little control over where cable is able to be run. With the exception of running with alongside feeder cable you should be fine.
Thanks Mac. You did answer my question. 

There seems to be an ongoing misperception that I am asking how to run power in studios.  I am not.  I am looking for and slowly recieving here, the practices used by LABsters on outside sound to show the people on the othere thread that adjacent lines are used all the time in live sound. 

Baring all*,
Andre

*Ethan, who did the acoustics 101 video is friend.  The closing is tip of the hat to him.


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Tim McCulloch

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Re: Power/Mic Line Separation
« Reply #16 on: April 23, 2011, 03:58:45 pm »

Thanks Mac. You did answer my question. 

There seems to be an ongoing misperception that I am asking how to run power in studios.  I am not.  I am looking for and slowly recieving here, the practices used by LABsters on outside sound to show the people on the othere thread that adjacent lines are used all the time in live sound. 

Baring all*,
Andre

*Ethan, who did the acoustics 101 video is friend.  The closing is tip of the hat to him.

Hi Andre

We've been taping 8/5 to the 80 meter drive snake for a long time and runs directly adjacent to the mic snake... and in 1 venue that bundle is on top of about 10 meters of the feeder run, too.  No problems.

As a stagehand I can recall one show running power to FOH that was physically separated from the mic snake, Mannheim Steamroller's Christmas show.  That was because the delay ring hangs were above FOH and their power was part of the FOH run.  High current, bigger magnetic field...  Tell your recording friends that we appreciate their commitment to input integrity, but live needs are more tolerant of miniscule noise than they are accustomed to.

Have fun, good luck.

Tim Mc
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Andre Vare

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Re: Power/Mic Line Separation
« Reply #17 on: April 23, 2011, 04:35:31 pm »

Hi Andre

We've been taping 8/5 to the 80 meter drive snake for a long time and runs directly adjacent to the mic snake... and in 1 venue that bundle is on top of about 10 meters of the feeder run, too.  No problems.

Tell your recording friends that we appreciate their commitment to input integrity, but live needs are more tolerant of miniscule noise than they are accustomed to.

Have fun, good luck.
Thanks for the info I am exactly looking for.  People seem to think that I am looking for "good enough".  I am not.  Good practices have to be followed throughout. 

The (huge) block that John Brandt and I are running into is people not understanding, much less accepting the "zero loop area" concept developed by Neil Muncy.  They just follow blind dogma expecting one or the other, not understanding how to use both.  This is interesting, and somewhat understandable considering how long it has taken Neil's "pin 1 problem" to be understood and mostly accepted.  That is consistent with traditional engineering.  The loop area" flies in the face of traditional engineering at first glance.

Andre
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JonathanSmith

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Re: Power/Mic Line Separation
« Reply #18 on: April 25, 2011, 07:10:50 pm »



When doing stage to FOH cable runs how close do you have the audio snake to the power lines?

T Taped together
0 0-2"
2 2-4"
4 4-8"
8 8-16"
M More than 16"
S Separate runs

Thanks.

Andre

Touring, 4-5 shows/week, 2k-5k seat arenas

300' input snake, power, and drive snake taped together. No noise problems.

With any touring I do, it is extremely rare for me to not have all of my FOH audio cables loomed together. With local one-off or corporate shows, I deal with whatever is given to me. Usually, lower channel count (<24 ch) snakes are not loomed together. Higher channel count snakes (48+ channels) are almost always loomed with power since I generally use a larger desk if I have a snake that size.
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Brad Weber

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Re: Power/Mic Line Separation
« Reply #19 on: April 26, 2011, 07:11:07 am »

There seems to be an ongoing misperception that I am asking how to run power in studios.  I am not.  I am looking for and slowly recieving here, the practices used by LABsters on outside sound to show the people on the othere thread that adjacent lines are used all the time in live sound.
I think that a critical aspect of this is addressing temporary runs not in conduit versus installed runs in conduit.  Whether studio or live sound, with the latter there can be practical factors and code requirements that relate to physically separating different signal types.
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ProSoundWeb Community

Re: Power/Mic Line Separation
« Reply #19 on: April 26, 2011, 07:11:07 am »


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