I wired a small residential sound studio, which is being expanded. The GC (All GC's know everything about everthing but know nothing about anything) is telling me that the homeowner is getting feed back from the electrical system? the only thing that I can think of that is causing it is dimmers that I installed. Anybody have any experience with studio's?

I'm trying to picture how you could possibly get feedback through the electrical system. It would seem that something in the electrical system would have to be microphonic, and cause enough disruption in the power feed that it gets through the filtration in a power supply, and back into the audio signal. I've never heard of such a thing in an electical power system.

Can you describe a bit more what the symptoms are?

[This message has been edited by SolarPowered (edited 11-12-2005).]

The GC just told me "feedback", I think that I am going to bypass him and talk to the homeowner.

Wonder if he means it's a "hum"? I recently had a customer complain to me about a hum coming from their sound system - they use the rec room for band practise. My thoughts too were the dimmers. Also the owner has put compact fluorescents all throughout the house, so I suggested he try turning off anything with dimmers and compact fluorescents when they practise. I still haven't heard back from him, so I'm assuming that was the problem.

The only problem with turning off all the dimmers, is that the dimmers control all the lighting in the studio.

Install resistive or autotransformer dimmers.

Would that do the trick, does Lutron carry those?

I just talked to Lutron, the only thing that they have is a Lamp Debuzzing Coil, which will stop some buzzing but not all. Lutron said the same thing, resistive or auto transformers, which will cut out all of the buzzing. Are thera any sites that I can check out? Thanks Classicsat!

Feedback-Hum... Hmmm... Sound studio....
3-wire circuits, and/or 2-wire circuits of seperate phases will do this too, if equipent is connected/re-connected on the audio side.

Most of the audio guys I used to work for would request 2-wire circuits of both or all 3 phases available at all points, if not only one phase available for equipment. Then they could choose whatever phase sounded best to them. I never heard the difference!

Feedback-Hiss... Hisss... Sound studio....
Electronic noise induced on circuit, could be from anything. Dimmers, LV, or flouresant lighting, electronic amps, TV in the neighbors house - anything. All of the amplifiers could just amplify the radio signals emitted from them. Thats a shielding problem in thier equipment, not yours.

They could also have grounding issues in thier equipment as well. Which could cause both.... I have installed many isolated grounds for dedicated circuits. And on one occassion a "Common refferance ground" which amounted to a #2 back to the main with a ground bar that they could attach jumpers to form different equipment. Also never heard the difference....

Ah, your killin' me, before I get all worked up, I think that I am going to talk to the homeowner to see exactly what the problem is. Thanks E

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.

The studio that I described is in a garage of a residential property, in which I wired in romex.

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?

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!

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.

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.

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.

"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).]

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.

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

Maybe some info in this link will be of help... http://www.epanorama.net/documents/groundloop/

Holy,moly this is turning into a circus. Nothing is easy is it? The track heads are 120v, 50w, r-20's.

Well you wanted answers, and suggestions.... You got 'em!

I got answers all right, but I'm stiil not sure what to do. I'm not complaining, I think this is a good thing. It never hurts to get other electricians imput, especially if they have already done something that you are looking for answers for.

I just reviewed some of the posts, one said something about multi-wire circuits, well I think thats how I wired it. The outlets are on a couple of 20-amp, 3-wire circuits and the lighting is on a couple of 15-amp, two wire circuits.

Good news! The homeowner is calling in a "studio engineer" later this week. The GC and I will walk thru it with him. I will ask as many questions as I can and take as many notes. I will keep you posted.

"Feedback-Hum... Hmmm... Sound studio....
3-wire circuits, and/or 2-wire circuits of seperate phases will do this too, if equipent is connected/re-connected on the audio side."

If that is the case, it may be as simple as moving some equipment around to be feed from the same phase. Otherwise, if amperage is low enough, make your 3-wire into 2-wire on the same circuit. That difference in voltage can manifest itself in various different ways when the equipment is fed from different voltages. Assume each piece has its own power supply, and drops voltage to whatever, and then reconnected to create another smaller voltage. Regulated or not... That differance in those two or more smaller voltages, could be what your hum is.

I can tell everyone here for sure that I definitely learned something from this thread about humming noises and the relationship it has to grouding. The most valueable lesson is to use Hospital grade MC whenever working a circuit for sound equipment. The neutral wire in a multiwire branch circuit works that much harder because of frequency difference in the equipment and that's being served (harmonics).

This site is really the best. Thank you all.

Oh, and good luck to the guy who has to fix the problem.

[This message has been edited by ShockMe77 (edited 11-16-2005).]

Me either, I will take advice about the hospital grade MC cable and I will wait to see what this engineer has to say.