Distance between conduits? Shielding?

Hello Aaron et all, As I understand I will have to separate audiolines from headphone-feeds and speakercacles (after amp) and also electric wires, right? So when I build plastic conduits into the soon to pour concrete floating floor, how far must the distance fom the audiolines be? Can I shield the conduits with something (aluminim foil?) when crossings or small distance is not avoidable? I intend to make the conduits not larger than 2,5 to 3cm inner-diameter. Do you know of problems with audiocables to pull through with this? I suppose their is no problem with ethernet, firewire, USB, monitorcables, etc? Other tipps? Thanks, Florian

Bump! :D

Florian, are you using plastic because metal conduit has tripled in price in the last year or so, or for some other reason? I ask because one of the benefits of using metal is that it can be bonded to your grounding system and will provide quite a bit of shielding, therefore requiring less distance between conduits for purposes of avoiding any crosstalk. As a general rule, power should be separate from everything, and if it MUST run parallel keep it at least a foot away from ANYTHING else, and at least TWO feet from low level analog (mic lines) - all digital (AES, SP/DIF, Midi, USB, Firewire, Cat5, etc) can be run in the same conduit, but should stay at least a foot away from power. I'd keep any low level analog at least 6" away from mid or high level analog, a foot away from digital, and 2 feet away from AC power. Speaker level stuff should be at least 6" from line level analog, and at least a foot from mic level analog. This isn't entirely arbitrary, I've actually had feedback problems when mic lines get too close to speaker lines, one instance I remember had about 3" gap between speaker and mic lines for about 10 feet and it howled like a banshee. We've all run line level audio in the same snake as mics for LIVE use and gotten away with it, but I wouldn't do that in a recording situation... Steve Rough synopsis - these are MINIMUMS, the way I'd lay it out - Power/12"/digital/3"/speaker-headphone/6"/line level/6"/mic level - these distances are between conduits, and are for METAL conduit. I'd increase them by at least half for plastic. (Keep in mind I'm probably overdoing, but once it's in concrete it's tough to change)

Thanks Steve,

(Keep in mind I'm probably overdoing, but once it's in concrete it's tough to change)

Yes, I got a general idea about the issue, but this is the reason I asked. What I do must be"rock solid" :D !

Florian, are you using plastic because metal conduit has tripled in price in the last year or so, or for some other reason?

Yes, but you convinced me to ask for prices of copperpipes again! This might be a dump question :oops:: all the cables come out of the floor and running to gear. Sometimes it's hard not to mix power, audio, etc., especially when the powerplug and the lines, etc are both at the backside. I had never a problem so far but I'm curious if there could be one or what you would take into consideration when building from scratch (both the CR and the desk)?

bump

I tend to run all power in a rack to one side of the rear of the rack (at the very back) and everything else to the opposite side - any digital lines I run down the center, and try to bundle any mic level stuff as far away from everything as possible. Any unavoidable crossings between power and the other stuff at right angles. Not all gear has the power connection on the same side, but you can usually run power from the connection on the rear diagonally to the opposite corner of the rear free space (behind the unit) if its power is backward from the rest of the gear; then, keep audio lines close to the chassis while running them to the "signal" side of the rack. For adjacent racks, you should alternate these choices; IOW, if you have 3 or 4 side-by-side racks (like in a producer's desk) the first one should have power on the left, signal on the right; the next one should have signal on the left, power on the right; then power on the left, signal on the right, etc - this puts all power from any two adjacent racks close to each other, and no signal bundle will be close to a power bundle. Copper conduit? Seems really expensive: I was referring to galvanized steel, known here as EMT (Electrical/Metallic Tubing) - its price has gone from about $3 USD per 10' stick of 3/4", to about $10 USD in the last year or so. Apparently due mainly to massive building spree in China, etc - same thing happened to 1" foam board insulation; last I checked, it was around $1.50 per sq. foot. (Fortunately us studio types don't care about foam board, but the conduit thing pissed me off :evil: ... Steve

Steve, thanks!

I will have lines and wires that I intend to install without conduit. What do you think about wrapping these in aluminium foil for shielding? Thanks Florian

I'm going to go with useless. But I could be wrong.

Actually, depending on the wires it could be worse than useless; I've not personally experienced this, but have been told that shielded speaker wire can cause feedback problems - something to do with excess capacitance, maybe? Not sure. If your individual wires are properly shielded, then adding aluminum foil may actually increase the capacitance of the wires which would roll off your high frequency a bit. Not a good idea. Possibly the single best reference for proper wiring of audio gear is Rane note 110 - http://www.rane.com/note110.html HTH... Steve

This may be a bit anal, but I want to do it as good as possible. Do you think its possible to shield electrical cables with foil which run within the concrete without duct? So they don't interfere with audiolines. Thanks.

Florian, Wrapping cabling in foil is a fine idea. There are a few considerations but it will help with electric field suseptibility. It is not going to help with radiated magnetic fields (like the 60 Hz and harmonics coming off the power lines) but it will keep them quiet. The idea is to get a good amount of foil around the cable to completely cover it, no open seams. Because you are in the audio frequency, ground the foil on the source end only (single point ground). The only reliable medium to shield from magnetic fields is mu metals. They make mu metal conduit but it is pricy. I'm at home but when I get to work I can give you a better idea of spacing. You probably know that fiber is immune to spacing requirements.

Hi Kent, thanks for your answer. Good there is an e-mail notifier cause I'm not much floating around in the forums these days...lot's of work.

I'm at home but when I get to work I can give you a better idea of spacing

That would be great! What is mu metal, never heard that?

You probably know that fiber is immune to spacing requirements.

What are you talking about here? Glassfiber lightpipes? I got no clue. Thanks again Florian

Hello,

What is mu metal, never heard that?

It's called permalloy, it is a metall used for shielding, read this: http://de.wikipedia.org/wiki/Mumetall (in german). Harald

Thanks Harald!

sorry Florian, didn't get a chance to go online today (or to work for that matter!). As Harold said, permalloy or mu metal is used to shield cabling from magnetic fields. As far as the fiber, yes lightpipe or any fiber optic cabling is immune to electromagnetic interference and therefore has no spacing requirement.

Thanks again Kent! As I see it, unfortunately lightpipe is not an option to replace all audiolines. Greetings Florian

I hear that. the systems out there are very costly still. I looked into spacing requirements. I have used the AKG 414 B/ULS sensitivity as a baseline. The noise floor of that mic is about 12.5mV/pa which is -38dBV. Using this and making the assuption that you are running them with 60Hz power lines (no real difference for 50Hz euro power), you can figure you should run the power lines and signal lines about 6 inches from each other to avoid interference. That distance is actually excessive but it is better to error on the safe side. The 6 inch number comes from separation practices used in the US Military for shipboard cabling practices.

Thanks a lot Kent! :)

I was reading through the thread and though it would be good to talk about some of the points brought up. EMI/EMC can be easy or it can be very hard depending on the system involved. Understanding how things happen is a full time job. I am fortune enough to work as an electromagnetic compatibility engineer. Knightfly, your post on speakers with shielding causing feedback I have not heard but hmmm.. capactive coupling can induce some strange effects at higher power levels depending on the way the shields are carried to ground. The frequencies would be right for magnetic fields and if your pushing the gas the current goes up, fields go up, coupling increases... looks like a bad idea. For foil to be effective (we buy it by the case) it is going to need a good path to ground. I would use use metal connectors and wall plates and ground the plate (*SIGNAL WIRES ONLY ON THIS PLATE, NOT POWER!!) then bring the foil to the plate and ground it by taping it down around the connection. That is your 360 degree bond to earth. Although single point ground is normal in these frequencies, it can be system dependent. We use a metal plate fabricated with feed-through connectors. since your in construction, your ahead of the game. Try grounding each end of the foil independently then both ends and see which, if any, has better performance. Use the plate for any coaxial runs and they will be quieter due to the bond to ground. It is actually common to use single and double braided shields. Some use foil and braid together. A very high frequency signal (well above anything we care about in audio), can weave in and out of a shield and be induced on to the signal cables, a problem called porpoising. This is due to the small holes in the braid that look electrically large at some frequencies. So they put a foil or a second braid to mitigate the problem. Alot of things in fighting EMI issues are a pain in the butt and a lot of up front work. But to go back afterward and "fix" things is far worse. Keep us posted on the progress. * for the hearing impaired. when I was in my teens I stuck a foil gum wrapper in the two prongs of an outlet, so this is for me in case I'm not listening. Man I'm glad I stopped doing that.

* for the hearing impaired. when I was in my teens I stuck a foil gum wrapper in the two prongs of an outlet, so this is for me in case I'm not listening. Man I'm glad I stopped doing that.

Yikes! Reading that made me remember something dumb I did as a teenager. Tried to hook up an electrical wire to a door knob to my step brothers bedroom door. :shock: :shock: :shock: Doh!!!

I wish I would have thought of that for my brother! He needed a wake up call. I think you win, I could only kill myself, you could have taken out the whole family! :shock:

Yeah, my Step-father saw the wires and asked what the hell it was. Boy, did I get a reaming for that one. And Grounded. (No pun intended). :roll: