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Author Topic: Light dimmer box EMI?  (Read 6663 times)

Leo House

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Light dimmer box EMI?
« on: April 21, 2010, 05:39:08 pm »

Forgive me if this is the wrong area, or whatever, I'm trying to get some advice for an issue I am having. I run the sound at the local community theater, and due to the setup, I work the light box aswell. The lighting box seems to be causing alot of EMI. It causes a buzz in the speakers and the audio recording, and also interferes a bit with my camera when I film the shows.

The light box, looks to be pretty much consumer-grade sliding dimmers, Here is a pic if that will help.

http://img204.imageshack.us/i/49495760.jpg/

http://img15.imageshack.us/i/dcfc0016.jpg/
(You can see in these pics, that the dimmer box is located right next to the sound equipment, and unfortunately, there isn't another place for it right now, and was done like this due to lack of volunteer workers to run everything)

Save for getting a new light system(which isn't possible at this time, as funding is a HUGE issue for this theater, and there are far greater needs in the restoration fund) so I am looking for a fairly cheap solution.

If I got some EMI shielding tape, like this  http://cgi.ebay.com/Aluminum-Foil-EMI-Shield-HVAC-AIR-DUCT-T   ape-58mmx25M-/180495605260?cmd=ViewItem&pt=Guitar_Access ories&hash=item2a06605e0c

and taped around the metal parts of the dimmer box (leaving the controls open obviously) do you think that would reduce the EMI enough to help? If not, what suggestions do you guys have that could help deal with this on a budget?



EDIT: I should also mention, as for as I can tell, there is no connection between the dimmer box's power, and the mixers power. The mixer is plugged into a regular wall outlet, as well as all the other equipment, but the Dimmer box is connected to more high voltage sources. There are lines, in blue tubeing, that run to it, and from it to another ox behind me(which also seems to emit a strong electrical field) and powers and controls 8-10 high powered stage lights. I'm still confused on how its setup exactly, but it appears that there is an awful lot of power running through that dimmer box.

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Leo House

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Re: Light dimmer box EMI?
« Reply #1 on: April 21, 2010, 05:52:26 pm »

I hope I'm not violating a rule by double posting, but there was already a reply on this before it got deleted, so I'd like to quote it and respond.(As get the reply in email, so I have it still)


Quote:

The first thing to determine is if you have a radiated or conducted EMI problem. If your battery-powered camera picks up the noise, you may have a radiated noise issue, but my guess, since you can hear the noise, is that you have a conducted EMI problem. Shielding won't help you with this; you need to eliminate any connections between the equipment. Paying attention  to proper grounding and shielding of the audio equipment will also help.


Well, for starters, the camera is running off outlet power, if that makes a difference. But the camera does not pick up the noise, its only in the mains and recordings, when the gain is really hot on the channels, (Regardless if there is actually anything IN the channel or not, it buzzes even in an open channel, also the buzz increases when the dimmers are mid way, lessens when raised up all the way, and almost non existent when they are down.)

Also, as I mentioned, there is no sound in the video camera, but there is significant quality loss from recording over there less then a foot away from the dimmer, as opposed to the center of the balcony more then 5 feet away from the dimmer.


I don't know the first thing about checking the ground and all that, but I believe it is more radiant, as I can use a mic and get the buzz 100 fold if I place it near the box while turned up high, which tells me there is SOMETHING emanating from it, and being less to 2 inches away from the sound mixer, I imagine that would cause an issue.

I've already tested for dust in the lines, disconnecting all the inputs, using another mixer, none of it has made a difference. The only thing that DOES make a difference, is whether the dimmer is off/on, and where the sliders are at at the time.
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Tony "T" Tissot

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Re: Light dimmer box EMI?
« Reply #2 on: April 21, 2010, 06:33:19 pm »

A couple of basics.

Power for lighting is usually not run through the control room.

Dimmers are usually closer to the fixture - i.e on-stage or in the wings.

Only small control voltage is usually feed to the control room, whether DMX or older analog control signals.

Many consumer-grade (home) dimmers will interfere with audio (you can search for information on how commercial-grade dimmers use chokes to mitigate RF, and various other schemes to reduce noise).

For about $300 you can buy a basic setup of 2 portable 4-circuit dimmer packs, and a 16 channel DMX control board (also works as a 2X8 (2-scene preset)). Just add DMX cable. Granted - not the greatest setup for flexibility or quality of dimmers in the world, but guaranteed to be better than what you have. It will probably cure your noise issues.
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Jon Evans

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Re: Light dimmer box EMI?
« Reply #3 on: April 21, 2010, 09:41:03 pm »

Yep, from looking at your photos, the lighting system you have is some homebrew thing that involves household dimmer switches.  This is not only noisy but far from code-compliant and possibly dangerous depending on how it was constructed.

I suggest trying to find the money to upgrade to a "real" light system like Tony suggested, but to integrate that with your existing lights would require some planning.

If the lighting system upgrade is something that you can take on the planning for, how about looking for model numbers / taking photos of your lighting fixtures so that we can recommend DMX hardware to get you started?

Also, you might want to see if you can find an electrician in your community who would donate an hour of his/her time to check out your existing dimming system.  Bonus points if the electrician has ever heard of DMX or worked with stage lighting before.
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Leo House

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Re: Light dimmer box EMI?
« Reply #4 on: April 22, 2010, 01:09:23 am »

Quote:

Dimmers are usually closer to the fixture - i.e on-stage or in the wings.


The light fixtures are actually pretty much right above me up there, maybe 7 to 9 feet up. They beam down to the stage.



Yeah, I'd much rather get a real light system going. $300 might be a bit much to layout for the theater right now, especially with everything else that needs to be fixed. The theater building is VERY VERY old, close to 100yo. We recently laid out quite a bit on the roof, before hand it leaked so bad, even leaking on stage.  If we get one of those grants we're trying to get for it, that'll defiantly be one of the things I'll push for.

Unfortunately, its not something I can plan, cuz I have NO CLUE what needs to be done, or what we need for as that goes. I've only been running a sound board for alittle over a year, with no actual official training. I don't know anything about setting up lights, or working with electric stuff like that.

Funny that you mention finding an electrician, the president of the theater counsel is actually an electrician, and probably the one who set up that dimmer system to begin with.


There is a guy that might know more about setting something up, I'll have to talk to him more in-depth.

Is there nothing else that can be done in the meantime, as a temp fix? Like that tape or whatever?  The box is metal, could I some how attach a grounding cable on it and make a faraday cage? If so, how would I go about attaching the cable to ground, cuz I dunno how to do it.



EDIT: Would it possibly help if I took better pics, or had video of the entire setup, and the lights and everything?
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James Feenstra

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Re: Light dimmer box EMI?
« Reply #5 on: April 22, 2010, 01:33:33 am »

based on the wall dimmer type lighting control you have, i'd be inclined to say there would be very little you could do in regards to fixing EMI from it, as large amounts of current is passing at a variable voltage directly beside your audio console

my immediate thought would be to move the lighting dimmers (including cabling leading into them) away from the audio desk if possible (even a few feet would help), as this will probably help to cut down radiated EMI

won't solve the problem, but might make it tolerable enough until a better solution can be put in place
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James Feenstra
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Gerry Seymour

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Re: Light dimmer box EMI?
« Reply #6 on: April 22, 2010, 11:38:29 am »

James Feenstra wrote on Thu, 22 April 2010 00:33

based on the wall dimmer type lighting control you have, i'd be inclined to say there would be very little you could do in regards to fixing EMI from it, as large amounts of current is passing at a variable voltage directly beside your audio console

my immediate thought would be to move the lighting dimmers (including cabling leading into them) away from the audio desk if possible (even a few feet would help), as this will probably help to cut down radiated EMI

won't solve the problem, but might make it tolerable enough until a better solution can be put in place


+1

You've already stated that just a few feet away with the camera makes a big difference. I'd look at putting these two consoles as far apart as possible. I know that makes it tough to run both, but you should probably have someone else running sound, anyway. You don't want to miss a cue on one because you're dealing with a problem that pops up on the other system (I did lighting design in a similar situation for 3 years).

As for planning, the folks on here can help you with that. We just need more info. Take pictures of everything. Get pics from far enough away that we can see how it's set up, then close enough that we can see details of what we're looking at.

Don't sweat the $300 too much at this point. Let's figure out what you need, then we can talk about how to find that funding. Trust me, it can be had, if you have the will to pursue it. In the end, you'll have better capabilities than the current equipment, and will have learned something real about lighting.
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Gerry Seymour

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Leo House

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Re: Light dimmer box EMI?
« Reply #7 on: April 22, 2010, 06:35:39 pm »

well, for starter lets make this one thing clear. If it came down to a choice, some other bloke can fiddle around with the light setup to his hearts content, but ain't no one else touching my sound board HAHAHAHAHA


Jokes aside, I'm a sound guy at heart, so doing the lights it just something I'm stuck with as it where. I only do it, cuz there are so few volunteers, and the placement of it, doesn't allow room for another person to get over there right. (They just get in my way when I'm doing sound) Currently, all we do is dim for slow songs, or brighten or more upbeat songs. (All we really do here is live music performances, search on youtube for Dixie Theater New Madrid, or Anna Catherine Dehart to see what is done here)

I have some video here, that we took to send to home makeover and/or any other place that can help get this place fixed up!

(If you can't see it right away, its still processing, should be done soon)


Also, the good news is, is there is only 1 more major show I really have to worry about for this season. Got two more fundraiser things, but other then that, we're pretty much done till august, so maybe we can get some stuff done in the mean time!
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Dan Mills

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Re: Light dimmer box EMI?
« Reply #8 on: April 25, 2010, 11:29:02 am »

Quote:

EDIT: I should also mention, as for as I can tell, there is no connection between the dimmer box's power, and the mixers power. The mixer is plugged into a regular wall outlet, as well as all the other equipment, but the Dimmer box is connected to more high voltage sources. There are lines, in blue tubeing, that run to it, and from it to another ox behind me(which also seems to emit a strong electrical field) and powers and controls 8-10 high powered stage lights. I'm still confused on how its setup exactly, but it appears that there is an awful lot of power running through that dimmer box.


If it is anything like a standard theatrical setup of say 15+ years ago, then the control box just handles small signals (say 10 or 15V max) and will not radiate much interference, it is the main dimmer rack that handles the power (the box behind you that probably buzzes when you move the controls).
You do seem to have some additional (possibly mains voltage controls beside the desk, which is a whole other can of worms).

Now dimmers work by chopping the mains and it is this action that generates the interference, getting audio cabling away from lighting cables (especially dimmer output cables) will help, as will common mode chokes on the audio lines.

Most of the interference will be being radiated by the cables between the dimmer and the lamps, with (probably) some getting back into the mains supply, so screening the dimmer itself will probably not help much.

To give you some idea of the energy involved, a standard theatrical lantern starts at 500W and 1KW is probably more common, so you could easily have 10+ KW running through that box (and being switched on and off 120 times a second).

FWIW, sound system buzz from dimmers is usually a symptom of a problem with the AUDIO wiring, not the lighting wiring (But this may or may not be true given your somewhat strange setup).

It might be worth asking the chief at another local theatre if they would take a look, most will do it for a beer, and they will typically be able to offer good advice (and may even know of some old theatrical dimmers in a junk room somewhere).

HTH.

Regards, Dan.
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Leo House

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Re: Light dimmer box EMI?
« Reply #9 on: April 25, 2010, 04:26:17 pm »

Yeah.  I know a guy that "might" be able to hook us up with something, but I'll have to talk to him more extensively.
Have to see if he is able to install aswell, or how that would work.

I'm not exactly sure what that other box this is behind me, but it doesn't have any controls that are accesable, its looks kinda like a small beaker box. (Its that thing on the wall in the beginning of the vid I posted)

I know there is quite a bit coming from both boxes actually, cuz the noise appears in audio recordings aswell, whenever its present in the speakers.  Possibly the EMI is effecting the actual board, and not the audio snake, or even both. The board itself is atleast 10 years old, maybe older so I dunno.


Not sure what you mean here tho.

Quote:

You do seem to have some additional (possibly mains voltage controls beside the desk, which is a whole other can of worms).


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