Buzzing fixtures

dshriver

Member
Hello everyone,

I'm hoping the collective wisdom here will be able to help me with a problem I'm having with my lights.

I'm the technical director of a performing arts center just north of Boston. We have 30 ETC Source 4 fixtures in the space on a Sensor+ Rack that is controlled by a Paradigm controller and an Ion. One of the presets we use most often has most of the fixtures at about 30-40%. At this setting all of the fixtures buzz, some more than others but all of them buzz. Its getting progressively worse. As one of our primary uses of the hall is classical chamber music any extraneous noise is a huge problem. I had numerous complaints last night from the light buzz. All my fixtures are lamped with HPL750 bulbs. What can I do about the buzzing?

Thanks!

David Shriver
Technical Operations Manager
Office: 978.546.7391 x 112
Fax: 978.309.8298
Email: [email protected]
Google Talk: [email protected]
Shalin Liu Performance Center
37 Main Street
Rockport, MA 01966
www.rockportmusic.org
 
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derekleffew

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...One of the presets we use most often has most of the fixtures at about 30-40%. At this setting all of the fixtures buzz, some more than others but all of them buzz. Its getting progressively worse. ... All my fixtures are lamped with HPL750 bulbs. What can I do about the buzzing?
Is it really getting "progressively worse," or is everyone becoming more aware, and thus more attuned to the issue?

I. Lamp sing is an unfortunate by-product of phase control dimming. Which is why dimmer, sine wave is used in the most critical of applications. Changing to sine-wave dimmers is probably not an option for you, but ETC does make Sensor D20 modules in three different dimmer rise time s: 350, 500, 800µs. I believe the only difference is the size of the choke (s). You might consider purchasing some high rise-time modules for your most problematic circuit s. [EDIT: the article cited below debunks this theory; moving on...]

II. If you regularly run 750W lamps at 30-40%, try 575W lamps at a higher intensity (perhaps about 60-70%; or even 375W lamps at 100%). Note that in both 750 and 575W HPL s, you have FOUR different lamps from which to choose:
From brightest to dimmest:
  1. 115V, standard life (300 hours) sometimes called high-output
  2. 120V, standard life (300 hours) sometimes called high-output
  3. 115V, long life (2000 hours) sometimes called HPL575X, or HPL575LL
  4. 120V, long life (2000 hours) sometimes called HPL575X, or HPL575LL
I don't know if any studies have been done to see which of the above lamps is acoustically the quietest. I suspect the 120V, standard life. Different lamp manufacturers may have different acoustic performance as well; perhaps try a different brand. As a rule, compact-filament halogen stage lamps are significantly quieter than high-wattage incandescent PAR or A lamps.

This article from ETC's wiki may prove enlightening: Risetime and Lamp Noise - What's the Connection? - Electronic Theatre Controls . Good luck, and let us know if you find a workable solution.
 
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dshriver

Member
My dimmers are D20DHR with 800ms rise time. My understanding is that these are already the quietest dimmers available. You're right, going to sine wave dimmers is not a viable solution for us. I'm lamping with 115v HPL 750 watt 300 hour GE lamps. I need the 750s because for many non-classical performances I need the extra punch of the 750. My US wall is a 30'x30' glass window over looking the ocean. Its beautiful but creates series backlighting issues. So the extra wattage is often needed.

I'd be willing to try different brands or types of 750HPLs but I do need to stay at that wattage. Increasing the dimmer to 100% cures the problem but that's not really a good solution. I've tried adjusting the intensity up or down slightly to avoid the buzz, but I find this spot moves. I'm guessing that lamp life, temp, run time, etc all have an effect on the % that causes the most noise.

Any other suggestions?
 

marmer

Member
We notice this too. We need the light output of the 750's and we usually run them at 85% or more, so we can usually manage the problem. For us it's worst with 250W PAR38's, not S4's. But they definitely get noiser with age, my guess is that the filament gets looser and vibrates more as the lamp ages. I've never changed a S4 lamp because of noise, although I have unpatched them for special recording situations. I have replaced PAR38's for noise a few times.
 

marmer

Member
dsh, this is probably a stupid question, but is there any way to hang the lights farther from the audience or put any kind of sound deflector between the audience and the lights? With us, I notice that the closer the light to the audience, the more complaints about noise, which makes me think that my S4's that are in the big hall way up in the grid are singing like Cecilia Bartoli but no one hears them.
 

derekleffew

Resident Curmudgeon
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... Any other suggestions?
I hate to suggest this but...
Take a tip from the movie industry. For only your most demanding shows, run the fixtures at or near 100%, and use a neutral density filter to control the intensity. L298 for 75%, L209 for 50%, L210 for 25%. Barbaric, expensive (but not as costly as some solutions), and inefficient/non-green, but it will work.
-----
...My US wall is a 30'x30' [18'x30'] glass window overlooking the ocean. It's beautiful but creates [-]series[/-] [serious] backlighting issues. So the extra wattage is often needed. ...
7235-buzzing-fixtures-slpc-hdr.jpg

Wow! What a dramatic space. Get some black drapes US to cover up that distracting and annoying view. :cool: Will probably help your acoustic issues as well.
 

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derekleffew

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What's the life expectancy of something like L210 in front of an HPL750 in a S4 Par?
(Guessing) better than one might think. But I wouldn't do it without heat shield and a color extender.

Also depends on the lens--the wider the lens, the faster the burn out (as JD explained to me [-]here[/-] somewhere; can't find it now :(). [EDIT: HA! Found it: http://www.controlbooth.com/forums/...parnel-deep-color-gel-lasting.html#post212449 . Turns out this wasn't the first time it eluded me, either.]
 
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chausman

Chase
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Could you possibly use fewer fixtures at a higher intensity?


Sent from my iPad using Tapatalk HD
 

millamber

Active Member
Just as an alternative to everyone else's great suggestions, is the humming coming from the lights or through the speakers? There could be a grounding issue in the sound system...
 

dshriver

Member
Thanks for the replies so far everyone.

My hang points are fixed so there's no way to move them farther from the punters. Sadly, they are only about 6 feet over the heads of my east/west balcony seating.

Using fewer lights at higher intensity doesn't really help. Already the classical musicians complain about the lights in their eyes. I run the full compliment at fairly low levels trying to fight the back lighting while keeping the musos happy.

I know its not hum from the audio systems. I typically have the amps turned off for my classical shows.

Are any of the brands of 750HPL lamps better than others? I'm not against moving away from my GE lamps. I could go with more diffusion and try running fewer instruments at higher intensity but I think I'll get complaints. Going with a 40% ND may be my best option, but it means changing gels when I go from classical to non-classical.

Other suggestions?

-d
 

gafftapegreenia

CBMod
CB Mods
Do you have any extra fixtures you can hang lamped at 575 or 375 for use on these events? Or perhaps you could use lights lamped at 750, but fewer of them, and with barrels of a wider spread than you currently use, in order to use lumen loss to your advantage?

Would adding top hats help reduce the visible glare from the lights? City Theatrical also has egg crate style louvers for the Source 4 Ellipsoidal.

I'd suggest you order a 750 from every major manufacturer and do a shoot out for your own ears. Lamp sing can be a very personal thing.
 
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DavidNorth

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My hang points are fixed so there's no way to move them farther from the punters. Sadly, they are only about 6 feet over the heads of my east/west balcony seating.

Well, that's certainly a challenge. I've been lurking on this one to see what other inexpensive creative solutions people could come up with.

Reflectors are wonderful for gathering light and sending it [more or less] one direction. Unfortunately, they do the same with sound. In addition, longer filament lamps such as PARs [notoriously loud!!] and 750W HPLs, are going to be more problematic than shorter filament lamps. If you look at the construction of a 750W HPL versus a 575W HPL, you will see that the 750W has two longer extensions of the filament. Going to a 575W lamp will certainly help but it will not eliminate the problem. Adding more load into each dimmer used will also help as forward phase dimmer chokes reach their full risetime rating when at a full load. So maybe you want to double up the loads into dimmers as your first step. I will tell you that running the dimmers very low are not going to help at all and is certain to make the situation worse. The best case would be to lamp down to 575W and then plug two to four into a dimmer wherever possible.

Six feet over the heads of complaining patrons is going to be really difficult to solve. In fact, that is specifically why Seattle Rep installed sinewave dimmers for all of their FOH box and balcony positions and then standard dimmers elsewhere. Brilliant solution.

There is a D20HR module which has a risetime of over 1000uS, but it is single density and might mean installing more racks.

Of course, another option is LED profiles.....

Try to place as many fixtures into as few dimmers as possible, and consider moving to 575W. Sinewave or LEDs will certainly be the best solution.

Hey, using ND and raising levels is a great idea too.

David
 

derekleffew

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David, have you any hypothesis as to whether the (assumed) thicker filament of a long life lamp would be quieter than a standard lamp? Or purposefully using the "wrong" (for the application, 115 or 120V) lamp?
 

chausman

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David, have you any hypothesis as to whether the (assumed) thicker filament of a long life lamp would be quieter than a standard lamp?

I know I'm not DavidNorth, nor an expert, but wouldn't the (assumed) thicker filament need more energy to vibrate, consequently making it produce less "noise"?
 

DavidNorth

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David, have you any hypothesis as to whether the (assumed) thicker filament of a long life lamp would be quieter than a standard lamp? Or purposefully using the "wrong" (for the application, 115 or 120V) lamp?

I don't, but will think about it. Ok, done some thinking [after I wrote the below and came back]. My lamp knowledge not being that of the level of some others tells me that the long life lamp is really just a higher voltage lamp marked at a lower voltage. If true, then it is therefore longer and noiser. Not sure about all this though....

It did remind of one other thing to note, though, that I should have remembered to pass on. My calibrated ear has heard a very distinct difference in noise output when comparing HPL aluminum base lamps and ceramic base lamps. Note that when the lamp buzzes, it is due to vibration and then everything around it vibrates as well. That means that an aluminum lamp base vibrating in a cast aluminum housing [in the case of a S4], is going to make a little metal-on-metal sound. Use ceramic HPLs as they are by far MUCH quieter. That likely explains why there are fewer noise complaints from Ushios - per above.

Try some 750W Ushios first....

David
 

derekleffew

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FMEng

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Just put neutral gray gel on the lights, such as Roscolux 97. It'll reduce the light intensity without affecting the color. That will cut down on the light output and allow you to crank the dimmers up, reducing filament sing. Cheap and easy to do with no lamp or hardware changing.
 

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