Distance between conduits? Shielding?

kent clemmons · Post by **kent clemmons** » Tue Dec 20, 2005 10:17 am

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.

the dreamer · Post by **the dreamer** » Tue Dec 20, 2005 6:49 pm

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

Greetings
Florian

kent clemmons · Post by **kent clemmons** » Wed Dec 21, 2005 2:09 am

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.

the dreamer · Post by **the dreamer** » Wed Dec 28, 2005 6:18 am

Thanks a lot Kent!

kent clemmons · Post by **kent clemmons** » Sat Dec 31, 2005 1:18 am

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.

Post by **Aaronw** » Sat Dec 31, 2005 2:08 am

* 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.

Doh!!!

kent clemmons · Post by **kent clemmons** » Sat Dec 31, 2005 4:32 am

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!

Post by **Aaronw** » Sat Dec 31, 2005 6:04 am

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).