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Unwanted "sound response" in lighting system

Discussion in 'Lighting and Electrics' started by soundlight, Apr 30, 2008.

  1. soundlight

    soundlight Well-Known Member

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    So I'm now working at a venue on campus called Uptown. The venue is 8 years old. There is a problem with the lighting system. When there is loud music playing, be it from a band or just playing back in someone's ipod, the lights seem to be slightly sound responsive. The stage lights, house lights, all of the lights that are up at all. They get slightly brighter each time the bass pounds. I know that this is not a light board problem for a few reasons: it doesn't do anything with our movers (roboscans of two flavors), it still happens when I tried my own board (Chauvet DMX-70), and it also happens when the light board (NSI MLC16D) is shut down and the system is on architectural control (ETC Unison, button stations, fader station) whether it is in preset mode (scenes 1-4 on the button box) or on manual fader control on the Unison fader panel. So I'm pretty sure that it's not control.

    The problem apparently began when renovations were done on the building close to and above the venue (venue is in the middle of a large dorm with two wings, one on each side), and the problem only got worse when more renovations were done last year. I am not sure what the nature of these renovations was.

    Rack is an ETC Unison rack with 10 dimmer modules in it (2x2.4K modules).

    Lamps involved are regular 120W PAR38 lamps, small halogen tracklight lamps, and 100W or so type A lamps in larger house lights.

    Any ideas as to what might be causing this? If we have to bring in an outside lighting company to fix it, that's gonna put a huge dent in the budget for next year that I'm trying to get through. I'm hoping that it's something that's just facilities' problem.
     
    Last edited: Apr 30, 2008
  2. Grog12

    Grog12 CBMod CB Mods Premium Member

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    Sounds like the sound system is getting its power from the same distro as the dimmer rack is.

    Where are the amps located in relation to the dimmer rack?
     
  3. soundlight

    soundlight Well-Known Member

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    Amps are in the upper level (+3' to the lower level) of the tech closet, and the dimmer rack is about 10' away, mounted on the wall, lower level, tech closet (they're at opposite ends of the tech closet). I wouldn't be surprised if they pulled power from the same breaker panel. In fact, they most likely do.

    However, please explain to me how there is a direct (and not inverse) correlation between brightness increase and volume thumps?
     
  4. Grog12

    Grog12 CBMod CB Mods Premium Member

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    I'm by no means an expert...but here is my theory:

    When the system is gearing up for the loud thump of bass its drawing an extra bit of power causing the dimmers to unintentionally dim. After it has sent the amplified signal to the speakers the power draw returns to normal but the minute delay between the amps and the speakers causes the lights to look like they're flashing with the sound.

    My poor man's crappy non technical explanation.
     
  5. soundlight

    soundlight Well-Known Member

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    I looked at the dimming response carefully, and there is no real dimming before the intensity increase. The lights immediately dim off right after the thump.
     
  6. TimMiller

    TimMiller Well-Known Member

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    On the sensor rack, go in and look at the line voltages (it may not display the voltage change fast enough but its worth a shot), Put on some loud music and see if there is a voltage drop every time the music thumps. If they have buck/boost or caps inline (may be built into transformer, esp if the transformer is designed to filter the line for audio or is a "green transformer" which has additional circuitry built in to make it more energy efficient). This is probably what you are seeing. Also another way set a channel to full (better if you have a non dim module) and put a voltage meter on there and then turn up the music you should see your voltage dropping with every thump. Amps, espically when they are running hard can draw some serious amperage. I have seen some generators rock back and forth, also blow out smoke every time the subs kick.
     
  7. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Close. But the audio amplifiers have no way of "gearing up for the loud thump of bass" as they don't know it's coming until it has happened. The power draw of the amps is (most likely) the culprit. You're most likely experiencing a slight brown-out AND a surge, as the voltage drops then over-compensates, then settles to normal. This makes the "lights look like they're flashing to the sound," due to the fact that light travels faster than sound, by a factor of 871,490. Your lamps are also of low wattage and thus react quicker to voltage fluctuations; this phenomenon may not even be noticed in a 1000W lamp.

    Speed of light = 299,792,458 meters/second
    Speed of sound in dry air at (21°C) 70°F = 344 meters/second

    According to someone's signature: "This is why some people appear intelligent until you hear them speak."
     
    Last edited: Apr 30, 2008
  8. Grog12

    Grog12 CBMod CB Mods Premium Member

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    Eh what can I say...I knew what was wrong...just not how to explain it. ;)
    That's why I have you Derek...to clean up my typing!
     
  9. JD

    JD Well-Known Member

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    Actually, there is a simpler explanation. The power amps are on a different phase leg than the lights you are observing, the neutral sag on that leg puts the other leg(s) over-voltage. If work has been done recently, I would have the neutral path checked out.

    My home has a 1000 foot run to the nearest pole transformer. When my sump pump starts half my lights dip.. the other half brighten. (Electric company totally not intrested in changing things.)
     
    Last edited by a moderator: Apr 30, 2008
  10. David Ashton

    David Ashton Active Member

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    Quick check on these theories run long cables to another part of the building to power amps and see if that solves problem, then follow up other ideas.
     
  11. STEVETERRY

    STEVETERRY Well-Known Member

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    I agree with this explanation. To verify: get a three-phase power analyzer on the dimmer feeds (like a Fluke 434 or Dranetz 4300) and take some snapshots. The cause should be evident immediately.
    ST
     
  12. soundlight

    soundlight Well-Known Member

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    Thanks all. I will see what I can do. I'll ask around and see if anyone on campus has a 3-phase power analyzer such as one of those. If that looks to be the problem, I'll just assume that the new staff that have come through have mixed a progressively louder house, which could be an easy explanation.
     
  13. soundlight

    soundlight Well-Known Member

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    So here's a kicker...it's happened while the sound system has been off. As in there have been thumps/bumps in the building and it has responded to them. How's that for weird?
     
  14. Dustincoc

    Dustincoc Active Member

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    Sounds like there is a loose connection somewhere and the vibrations are making it momentarily lose contact
     
  15. TimMiller

    TimMiller Well-Known Member

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    I bet you have a loose neutral or ungrouded conductor somewhere (ie hot leg, current carrying conductor) I'd go to the disconnects and hit them to see if you can make anything flicker. I'd also hit on the side of the dimmer rack to see if there are any problems. It could be that the CEM is just not tightly inserted into the rack.

    WARNING!!!!!!
    If reinserting the CEM its best to power off the rack by turning off the disconnect, even though i have been told they are hot swappable, i like to do things the safe way, and not freak their little brains out.
     
  16. Goph704

    Goph704 Active Member

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    Yeah, that's sounding more and more like a loose neutral, you mentioned diffrent levels to the theateater, does this happen on other floors as well? If it does you might be able to trace back the problem and see what home run it's at, my bet would be that it's somplace close to the main breaker for the building, the problem there is you need kill building power and get licenced to take care of the problem. If you can trace it out first however you'll save a lot of time and money, ( and possible problems in the future.) You might advise your college not to go with the lowest bidder this time.
     
  17. JD

    JD Well-Known Member

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    This is the line that worries me the most. Some contractor may have tied something into the existing system and left a neutral bug loose, or you could even have an underground cable cut that is degenerating. The fact that any powerful noise in the building causes voltages to vary is a HUGE red flag! (pointing more towards a loose bug) Because lights get brighter, the neutral path comes most under suspicion. I would suspect there are voltage sags occurring somewhere at the same time, but they may just be out of view.

    In any case, this is something serious and should not be written off as an inconvenience before an extensive examination is done. There IS something wrong and it needs to be fixed.

    (Stern warning directed towards venue owner, not you ;) )
     
    Last edited: May 1, 2008
  18. soundlight

    soundlight Well-Known Member

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    I hope to be meeting with the electrician and the adviser at the venue before I leave for summer.

    I was thinking that this could also be dirty dimmer modules...I can almost guarantee that the dimmer modules have not been cleaned in all 8 years of being used every weekend.
     
  19. JD

    JD Well-Known Member

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    Although dirty dimmers can cause problems, such as overheating and reduced device life, I am hard pressed to think of how it would manifest itself the way you described. Even if we add poor contact, such as an oxidized connector, the most you would run into would be dimmers that cut out to black. If the DMX is being interrupted, the dimmer would either "hold" or drop to black. If the gate pulse is being lost, again the channel would go black. Same with the power loop in & out.
    As for the movers, the lamps are ballasted, so minor variations will not show up too much, or in the case of E-ballasts, not at all.

    When incandescent lamps are at a mid point setting on a dimmer, it doesn't take much variation in voltage to be able to see it. Conversely, you are probably not going to notice it on a lamp that's on full. If you can, then that is a bad sign.

    The fact that building noise affects it causes me great concern.
     
  20. TimMiller

    TimMiller Well-Known Member

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    I'd see if they could put an oscilliscope on the line and see if they can tweak different things to trace down line noise. I'd be currious to see what is happening. I have also learned in my commerical wiring class, that if you have a light fixture with two balasts (such as a dual ballast flourescent so it can be "dimmed", not exactly dimming but turning off half of the lamps)for example that is comming off of two phases of a three phase power source, you must run a separate neutral for each of those two phases or you will get some weird voltage spikes. Instead of a 180 degree curve, you will also have a 180+1.75 degree curve comming in, in front or behind your 180 degree curve which will really create some weird problems. So somewhere in the system it could be as simple as that, but from the sound of it its not. Now if they did run multiple cables for one neutral (ie 2 3/0 cables from a disconnect to a switchboard for the neutral) (if you get into a wire size that is too big for your application, you can split the load down two cables, you do have to do some derating to find your proper cable size), they have to be the EXACT SAME LENGTH, or you will also get some very bizzare phasing issues.

    Hope i didnt confuse you too much, but these are some posibilites of things that may be happening.
     

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