Theater Lighting / Audio System Help

[Marc Hayes]

SO, some wonderful electricians installed a Strand dimmer system and new feeds to it, new breaker panels, etc. When they ran power for us doing audio, they were told to pull from separate service that was apart from the dimmers for the obvious reasons of hum and such when the lights dim. Well, of course they didn't take that seriously and pulled audio power from the same panel that was tied into the new dimmers. Now, with the lights at anything but full on or full off, the audio system hums.

Aside from running new service for audio, is there anything that can be done to rid the hum?

Just trying to help these guys out.

Thanks!

 

[TJ Cornish]

Re: Theater Lighting / Audio System Help

SO, some wonderful electricians installed a Strand dimmer system and new feeds to it, new breaker panels, etc. When they ran power for us doing audio, they were told to pull from separate service that was apart from the dimmers for the obvious reasons of hum and such when the lights dim. Well, of course they didn't take that seriously and pulled audio power from the same panel that was tied into the new dimmers. Now, with the lights at anything but full on or full off, the audio system hums.

Aside from running new service for audio, is there anything that can be done to rid the hum?

Just trying to help these guys out.

Thanks!

Correctly designed audio gear should reject this kind of noise in most cases. Separating the feed may or may not help; issues like this are usually grounding related, and just putting the lights on a different panel may not change the situation much.

Standard troubleshooting steps apply - when does it buzz? Just amps on? Mixer through speakers on? Certain channel lines? How is grounding in the space done? What isolation has been put in between lighting control and audio?

 

[Marc Hayes]

Re: Theater Lighting / Audio System Help

Correctly designed audio gear should reject this kind of noise in most cases. Separating the feed may or may not help; issues like this are usually grounding related, and just putting the lights on a different panel may not change the situation much.

Standard troubleshooting steps apply - when does it buzz? Just amps on? Mixer through speakers on? Certain channel lines? How is grounding in the space done? What isolation has been put in between lighting control and audio?

If the lights in the room are full off, everything in audio world is perfect. If the lights in the room are full on, everything in audio world is perfect. As the lights decrease from 100% intensity, the hum gets louder until lights hit 0%. Then again at 0%, all is happy. As the dimmers create their own hum, it matches in pitch to what is coming from the audio system.

It happens across the whole audio system, just as long as the amps are on. Shut the mixer off, still hums. Only time it stops is with the amps off.

Any thoughts more more insight I can give?

Thanks!

 

[Silas Pradetto]

I think they just had a thread about this on here. Neutral and ground were bonded in the subpanel when they should only be bonded at the service entrance. Check that first.

Sent from my DROID RAZR

 

[Arthur Skudra]

Re: Theater Lighting / Audio System Help

You may end up having to put in a shielded isolation transformer for your technical power.

Some really good resources here:
Middle Atlantic Products -

http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf

 

[Rob Timmerman]

Re: Theater Lighting / Audio System Help

Correctly designed audio gear should reject this kind of noise in most cases. Separating the feed may or may not help; issues like this are usually grounding related, and just putting the lights on a different panel may not change the situation much.

Standard troubleshooting steps apply - when does it buzz? Just amps on? Mixer through speakers on? Certain channel lines? How is grounding in the space done? What isolation has been put in between lighting control and audio?

Yep. While those Strand dimmers may be putting some harmonic currents (noise) onto the neutral and phase conductors, they don't touch the ground unless something is wired wrong. And no audio gear should be doing anything with the neutral and phase conductors except converting to DC for power. So that noise shouldn't go anywhere audio signal paths.

Now, you may have issues with induced noise due to unshielded cables or susceptible equipment, so you may need to do some troubleshooting to find those issues.

 

[Brad Weber]

Re: Theater Lighting / Audio System Help

SO, some wonderful electricians installed a Strand dimmer system and new feeds to it, new breaker panels, etc. When they ran power for us doing audio, they were told to pull from separate service that was apart from the dimmers for the obvious reasons of hum and such when the lights dim. Well, of course they didn't take that seriously and pulled audio power from the same panel that was tied into the new dimmers. Now, with the lights at anything but full on or full off, the audio system hums.

Were they actually contracted or directed by the Owner to provide something other than what was provided? If so then maybe the place to start is to push for that to be corrected.

Sounds like it might also not be that surprising if they bonded neutral and ground at the panel.

 

[Craig Hauber]

Re: Theater Lighting / Audio System Help

I've done many club and small theater jobs where there is only one panel in the building -with neutral and ground bonded as per code -so it's possible to do this and not have problems. My guess is that it isn't power-line or supply problems but issues with the audio wiring.
A typical ground loop will bring properly wired and running dimmers noise to the forefront.

 

[Brad Weber]

Re: Theater Lighting / Audio System Help

SO, some wonderful electricians installed a Strand dimmer system and new feeds to it, new breaker panels, etc. When they ran power for us doing audio, they were told to pull from separate service that was apart from the dimmers for the obvious reasons of hum and such when the lights dim. Well, of course they didn't take that seriously and pulled audio power from the same panel that was tied into the new dimmers.

I've done many club and small theater jobs where there is only one panel in the building -with neutral and ground bonded as per code -so it's possible to do this and not have problems. My guess is that it isn't power-line or supply problems but issues with the audio wiring.

There could be just one panel, which would then be the service panel, but it sounded from Marc's description as though one or more new subpanels were added as part of the lighting install and if so then neutral and ground should be bonded only at the main service panel and not at any subpanels. I've had enough experiences with Electicians stating that neutral is not bonded at subpanels, that two circuits are served off the same or different panels, that an isolated ground is maintained, that there are no shared neutrals, etc. only to find it to not be true to know that such things do happen and that you can invest a lot of time, energy and money trying to address issues with the electrical service that really need to be corrected anyways.

 

[Mike Caldwell]

Re: Theater Lighting / Audio System Help

I had the same problem a couple months ago at an audio install I did. Ground and neutral bonded in a sub panel was the main problem along with a handful of other issues I found after opening up all the breaker panels.
Here's the link to the thread http://soundforums.net/lighting-ele...m-causes-buzz-hum-circuit-breaker-panels.html

Let us know what you find.

 

[Kevin Maxwell]

Re: Theater Lighting / Audio System Help

If the lights in the room are full off, everything in audio world is perfect. If the lights in the room are full on, everything in audio world is perfect. As the lights decrease from 100% intensity, the hum gets louder until lights hit 0%. Then again at 0%, all is happy. As the dimmers create their own hum, it matches in pitch to what is coming from the audio system.

It happens across the whole audio system, just as long as the amps are on. Shut the mixer off, still hums. Only time it stops is with the amps off.

Any thoughts more more insight I can give?

Thanks!

After doing everything that has been suggested if you still have a problem it would be nice to know if it is the entire dimming system or just part of it. I have been doing theatrical shows in one venue for a while now but the most recent show I had a noise problem with the lights. I narrowed it down to affecting one piece of sound gear and was able to work around it for the show. I realized that I hadn’t done any sound system testing with the lights being dimmed and then the problem showed up when they started dimming them.

They told me they had made a bunch of lighting changes. This system uses distributed dimming, most of the dimmer packs are the big long ones on the light battens.

I didn’t get a chance to do this on the last show due to timing problems but I am going to do it on the upcoming show. I call this divide and conquer. Have them run all of the lights up and down and listen for the noise. Then have them only do it with half the lights then the other half. Did you have noise on one half and not the other? Have them keep on dividing in half and see if you can pin it down or narrow it down. I had a problem with lighting interfering once and it turned out to be a bad electrical connection that was arcing and I was picking it up in sound. It happened to be at a video shoot and when we replaced the bad lighting cord everything was fine. I have also seen a lot of bad stage pin connectors on lighting fixtures. Loose connections in the stage pins themselves and the pins just needing to be spread a little bit to make better contact.

I was once hunting down a noise that I was pretty sure was caused by the lighting, But I couldn’t find it and it was really buried in the noise floor. As we were breaking down there was a moment where everyone got quite for some reason. All of the sound gear was off and I suddenly noticed the noise again. It was a noise in the room itself that we were hearing acoustically. This was a long time ago but I think it was what I now know to be the lamps themselves singing, it’s the filament vibrating.

The “shut the mixer off it still hums” reminds me of a sound system in a church that had a problem that even when you shut off the amps you still has a noise in the monitors. It turned out the amps were by the mixer and the wiring was so tangled with a lot of other wires including alarm wires down a hallway ceiling, including laying on top of florescent lighting fixtures, that noise was being injected into the wires. I pulled all of the wires out and restrung them and all the noise problems went away.


Don’t you know the reason that a sound system hums?

It doesn’t know the words.

So teach it the words and the humming should go away.

 

[Mike Caldwell]

Re: Theater Lighting / Audio System Help

The “shut the mixer off it still hums” reminds me of a sound system in a church that had a problem that even when you shut off the amps you still has a noise in the monitors. It turned out the amps were by the mixer and the wiring was so tangled with a lot of other wires including alarm wires down a hallway ceiling, including laying on top of florescent lighting fixtures, that noise was being injected into the wires. I pulled all of the wires out and restrung them and all the noise problems went away.

Noticed a very similar thing at a church a while back. I was there working on some floor box jacks and heard buzzing coming from the monitors. I knew the system was powered down, completely disconnecting the speaker cable did not get rid of it. The inductors in the monitors where picking up the RF hash from the dimmers on the sanctuary lights. Changing the monitor position you could make it better or much worse, the monitors are JBL 712. The sound system is actually amazingly quiet, I have heard that the guitar players sometimes have noise issues, no big surprise there!

 

[Craig Hauber]

Re: Theater Lighting / Audio System Help

There could be just one panel, which would then be the service panel, but it sounded from Marc's description as though one or more new subpanels were added as part of the lighting install and if so then neutral and ground should be bonded only at the main service panel and not at any subpanels. I've had enough experiences with Electicians stating that neutral is not bonded at subpanels, that two circuits are served off the same or different panels, that an isolated ground is maintained, that there are no shared neutrals, etc. only to find it to not be true to know that such things do happen and that you can invest a lot of time, energy and money trying to address issues with the electrical service that really need to be corrected anyways.

Sorry Brad, I came across wrong with that,
I was referring more to the concept that sound & lights can co-exist on a the same service even if hooked up unintentionally to that service. They can also co-exist in the same little equipment closet or even (gasp!) in the same rack. (not recommended but I have had to service systems I've found like that)
Yes, service and panel issues need to be addressed asap -and honestly it's very easy for an installer to verify with a few minutes with an electrician just walking around and opening panels if they aren't already open. -They never like that though, but usually once they've gotten a tour of the "cool & fun" equipment I'm installing they warm up to it (Sound & Video always excites the electrical trades after they've been doing hvac all day!)

I was more politely trying to lean the direction of it being an audio system problem and not a lighting problem. Filament dimmers are what they are. they will dump crap on the neutral no matter what. I've seen and worked on audio rigs surrounded by worst-case situations that are studio-quiet and others with iso ground distribution and special service transformers that are noisier than an abused Fender twin. This is not to say that there isn't something wrong with the lighting, just don't assume the audio system is perfect and waste a whole bunch of hours chasing your tail with the lighting rig.
My odds are highly on the side of audio wiring being the primary fault (-just from my experience.) And it could be something really simple or a manufacturer screwup that would have even the most competent installer scratching their head (Like the neutral/ground reversed molded IEC cable on the primary system DSP I found once -or the entire patchbay wired hot/gnd reversed
And by no means am I also saying that it's easy! You hope you can find the problem fast but sometimes it can double your install labor hours unfortunately.