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Shielded Smurf Tubing?
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Resort Records
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#1
21st June 2013
Old 21st June 2013
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Shielded Smurf Tubing?

Hi all,

Some of my in-wall cable runs must necessarily cross over existing electrical wires - within an inch or so. I searched the 'net but couldn't find anything like shielded smurf tubing. Is there such a thing? Or, could I simply wrap my smurf tubing with electrical shielding tape where it's within 12" of electrical wiring?

Any help is greatly appreciated.

Dave
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21st June 2013
Old 21st June 2013
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Dave,

You don't need to do that. Separating the grounds and lines in this fashion will create more problems than it solves anyway.

NOTE: I recommend steel conduit for all electrical runs or steel partitioned channels for the electrical to run right next to the audio lines so that any 'current coupling' is eliminated. But in quite a few of our builds steel conduit has been unavailable and they experience zero problems. - In large concerts they will run power from the stage all the way back to the house mix console to power it, computers, rack gear, etc., all of which pull a substantial amount of current and there is no leakage into the audio snakes (mic lines!!) the run directly coupled to the electrical. They are usually bundled together with duct tape. NO hum, no buzz due to this. Hum and buzz in a studio is caused by loop area. Collapse the loop.

I have posted quite a few articles on my publications page dealing with studio wiring. You may find it helpful. - In all of our builds we use a Zero Loop area plan where all wiring (AC & Audio) remain in very close proximity to each other. Done right, this is nearly 'perfect'.

Cheers,
John
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John H. Brandt
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(American) in Jakarta, Indonesia

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#3
21st June 2013
Old 21st June 2013
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It's called 'Flexible Metal Conduit'. It's in the normal power line electrical stuff section. It may not shield as well as rigid conduit (EMT).

But read Mr. Brandt's post first.
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22nd June 2013
Old 22nd June 2013
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Thanks, guys!

John, I'm amazed by your story re bundling analog and electrical lines and am trying very hard to understand your document on Zero Loop Area Design (but it's a bit beyond my capacity, quite honestly). And when you say that separating grounds and lines can create more problems than it solves, it challenges everything I know (admittedly, very little) of the subject. I mean, isn't it common knowledge that electrical and audio should be separated by 12" or more?

Anyhoo, I don't know how zero loop area relates to my situation, given that the electrical lines I'm worried about don't drive my studio at all - these are other circuits running through the walls to other rooms and I can't replace them within budget.

I hate like hell to waste everybody's time with stupid questions, so I've thrown together a drawing that pretty well demonstrates my layout. [It's my first electrical diagram, so please be forgiving.] Only the red circuit - actually, it represents multiple circuits - is pre-existing and cannot be modified within budget. These run floor-to-ceiling, laterally, and all over, and can't be avoided (without taking the long way around, I suppose). The rest have been laid but the walls haven't been sealed, so it's not too late to move/change them. Oh, and few of the analog and digital audio lines have been run yet, FWIW.

Oh, and Speadskater, are you suggesting that I use flexible or rigid metal conduit around my analog and digital lines? That I can do! Easy-peasy.

Thanks, guys. I apologize for being such a dolt. Seemed like an easy question when I originally asked it. <sigh>
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23rd June 2013
Old 23rd June 2013
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Well, it's 'common' information on the internet.. but not knowledge. 20-25 years ago, being fairly knowledgeable of electronics and electrical, I also advocated the separation of the electrical lines from the audio lines by at least 12". - My mind was made up and I didn't think about it until I had the opportunity and pleasure to work with Neal Muncy on an installation.

His common sense, analytical reasoning, AND the results obtained with this technique of zero loop area won me over. I have been building ZLA ever since.

Your question about the red circuits... won't hurt anything. It is the ground lines that are of concern. They should represent a single, low impedance, unified path to ground. I have put some new articles about Studio Wiring on my publications page.

Your audio lines are balanced, right? No 'induction' will occur. You're fine. Have you experienced any noise problems?

A NOTE on your CR design: is that drawing in scale? You know that your mix position is nearly, precisely in the center of the room.. both ways?

Cheers,
John
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23rd June 2013
Old 23rd June 2013
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Thank you so much, John! That's very helpful. I'll go check out your new articles too.

To answer your questions, lines are balanced and, no, I've not experienced any noise problems - I'm just trying to make certain that I don't build any new problems into my room. Believe you me, if it can be broken, I will break it. :D

Yeah, I realize the mix position isn't ideal in this drawing. For clarity, not shown are the rather large wide-band absorbers - it's a non-environment design. It's difficult to predict but, hopefully, will negate the effects of a poor listening position.

Thanks again!
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23rd June 2013
Old 23rd June 2013
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NE.. great! Your back and side walls, then are NOT really THERE.. they are further away. No worries, then. It's the hard room boundaries that count, not the treatment boundaries.

Cheers,
John
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23rd June 2013
Old 23rd June 2013
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I wasn't making a suggestions about your studio, I just gave the product a name.

About small loop area:
In general, all analog signal cables going from area 'A' to area 'B' should be bundled (dressed) together. All AC power cables going from area 'A' to area 'B' should be bundled (dressed) together. But the signal bundle and the AC power bundle should be separate.
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24th June 2013
Old 24th June 2013
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Quote:
Originally Posted by Speedskater View Post
I wasn't making a suggestions about your studio, I just gave the product a name.

About small loop area:
In general, all analog signal cables going from area 'A' to area 'B' should be bundled (dressed) together. All AC power cables going from area 'A' to area 'B' should be bundled (dressed) together. But the signal bundle and the AC power bundle should be separate.
Yes.. but not TOO separate. You cannot run electrical in the same conduit as low voltage wiring. It's illegal and unsafe. You want to run your Electrical PER CODE in conduit - RIGHT NEXT to your audio lines so that there is no 'loop' in all the ground wires. There are ground lines in the audio and the electrical.. they terminate at both ends AT THE SAME PLACE. Do not introduce a loop in between the source and termination.

Cheers,
John
#10
24th June 2013
Old 24th June 2013
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Speedskater is offline
That sounds like a good plan. The field from power lines in conduit/trunking is a lot smaller than some people think. For those using Romex®NM (Non Metallic) twisting each cable is a good thing.
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