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#58585 11/13/05 12:59 AM
Joined: Jan 2005
Posts: 5,445
Likes: 2
Cat Servant
Member
All I can do is describe a recording studio that I had the pleasure to demolish....

They had run a heavy-gauge bare copper ground wire to everything, even though EMT was the wiring method. Rather like an "isolated ground" system, except standard devices were used, and the bare wire obviously touched the pipe in many places.

#58586 11/13/05 08:18 AM
Joined: Nov 2005
Posts: 187
HCE727 Offline OP
Member
The studio that I described is in a garage of a residential property, in which I wired in romex.


Hank
#58587 11/13/05 06:44 PM
Joined: Jun 2005
Posts: 821
S
Member
Is it possible that the return path (neutral) is working harder than necessary because of the sensitive electronic stereo equipment being used on the circuit?

#58588 11/13/05 07:28 PM
Joined: Jan 2005
Posts: 5,445
Likes: 2
Cat Servant
Member
Just thought I'd think this one over a bit....

"Feedback"...hmmm...first of all, what are the acoustics like? A sound studio should avoid right angles and hard surfaces. You don't want sound bouncing back and forth.

As far as the electric goes....well, what will create electronic or radio "noise?" Magnetic fields and sparks, I would guess.
Magnetic fields can be "blocked" by using metal raceway (pipe or MC/AC).
Sparking can occur at a loose fitting. making everything an "isolated ground" will reduce the chances of current flowing through the conduit. True IG, that is, with IG devices and an insulated green wire.
You might get arcing inside switches and such....probably best to place them outside the booth.

Any kind of transformer will make a 'hum." There is somethin to be said for all-electronic fluorescent ballasts. Also, take pains to keep all your wires away from transformers and ballasts (just like you would do with data cable).

Data cables and speaker wires might also pick up a "hum" from running alongside electric wires (such as romex).

Beyond that, weird things can happen with the sound recording equipment, especially if any of it has been home-built or "improved" by the customer. Many of the times, a grounding problem is discovered with the equipment.

Finally, don't forget the obvious. In absolute silence, you will often "hear" a high-pitched whine. This is simply the blood flowing through your ear!

#58589 11/13/05 11:10 PM
Joined: Nov 2005
Posts: 187
HCE727 Offline OP
Member
A friend of mine told me about using hospital grade MC cable with isolated grounds and outlets. The lighting in the studio is all 120v track lighting, with small heads, but they are only 7' off the floor. the GC did not want any recessed lights because the sound traveling upstairs.The more I think about it I think it is the dimmers.I still want to talk to the homeowner, because the GC is one of those kwknow it alls.


Hank
#58590 11/13/05 11:56 PM
Joined: Dec 2004
Posts: 209
H
Member
I recently built some residential theaters and was working with a sound/media specialist. He was very emphatic that we used the same phase (residential...the same buss) for all the receptacles that served his equipment. Perhaps, if you have some of the circuits mixed, you can move them in the panel and get them all on the same buss. He explained that it could create a buzz...but it went right over my head.

#58591 11/14/05 12:21 AM
Joined: Apr 2002
Posts: 914
E
Member
HLC... is onto something. I've seen problems like this with home theaters. The audio guys call it a ground loop, but what fixes or prevents it is to keep lights off the circuits with the equipment and preferably on a diferent phase. Keep all sound circuits on the same phase and don't use multiwire circuits or share neutrals. Use dedicated ciruits (on the same phase) for as much as posible.

#58592 11/14/05 12:24 AM
Joined: May 2003
Posts: 2,876
E
e57 Offline
Member
"In absolute silence, you will often "hear" a high-pitched whine. This is simply the blood flowing through your ear!"

Is that what that is? I thought it was the voices of christmas' past...

"The lighting in the studio is all 120v track lighting, with small heads."

"Small Heads" If you mean MR-16's, each one has a small radio, I mean electronic transformer in each one. And would result in a high pitched ringing, around amplified equipment. Dimming would change the pitch intensity.
----------------------------------
And that too can be a shielding or grounding problem in thier equipment.

When you go, have them show you the offending equipment, look for a ground lug on the case. (Usually on the back) And take a piece of #12 green to a known ground, like a face plate screw of a receptical as a test, it may help.... If it does think about giving them a ground bar to go to. Its worth a shot.

You are going to have to fill us in when you go....



[This message has been edited by e57 (edited 11-14-2005).]


Mark Heller
"Well - I oughta....." -Jackie Gleason
#58593 11/14/05 07:17 AM
Joined: Nov 2005
Posts: 31
J
Junior Member
For a sound studio you really need a special isolation transformer, a torodial type which slightly different 120 vac. They need a 2 pole breaker for each 120 circuit. This 120 measures 60 volts to ground.

But there are several other things that can cause hum.
1. Any flat cable, romex, is an antennea. To eliminate hum you need twisted wire and/or sheilded cable, medical MC would work. An example, you must use stranded wire in gas pump installations so it will twist and eliminate interference.
2. Even the water pipe, if used as a grounding source, can emit very low frequency.
3. You can use no electronic dimmers or floresents with electronic ballasts.
4. Keep the equipment cords as short as possible. No extension cords

Hope this helps a bit.

#58594 11/14/05 01:49 PM
Joined: Nov 2000
Posts: 246
R
Member
I just received my October 2005 issue of EC&M, and wouldn't you know it, there on page 22 is an article titled "Finding and Fixing Ground Loops in AV Systems".

One paragraph states that "...noise is most often a mixture of 60 Hz harmonics and other high-frequency noises that normally exist on AC power lines...This should not be confused with "random" noise, which manifests itself as a hiss in an audio system...Ground noise produces artifacts such as hum, buzz, clicks or pops..."

My suggestion would be to hear firsthand what the "noise" is, then go from there.

Look for a copy of this mag at your local library if you don't subscribe. The web site for EC&M does not have this issue on their site, yet. (www.ecmweb.com)

Rick Miell

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