Noisy lights - need a better explanation!

[chilights]

Hi! I work in a facility with multiple venues. One venue is used mainly for live acoustic music performances. The venue is lit by about 20 Shakespeares. I'm guessing they are at least 5 years old. (The space was built and spec-ed before I started working here.)
So here's my problem: Occasionally some of the lights make a loud popping noise that lasts a few seconds. Those who play in the space are furious that this happens and are demanding I do something about it. I understand the sound to be from the metal of the fixture expanding/contracting and either making contact with the quartz lamp or with other metal parts of the fixture. I have explained this to the music folks that there isn't much I can do about it, but they refuse to believe me. The room is often kept at a cool temperature, and the lights are near the vents, so the popping occurs even if I preheat the lights for a few hours. There are no other hanging positions for the units, so moving them is not an option. Nor is adjusting the temperature in the space. My only solution for those who are irritated by this occasional sound is that we switch over to LEDS. The reason I'm so frustrated is that I am being blamed for the noise as they tell me that it never happened before I started working here. Also, no one believes me when I tell them what is causing the popping, so they've started getting other people involved who really don't need to be a part of this. I'm the only person with a lighting background, that doesn't seem to hold any weight.
So, long story short, does anyone have any sort of link to a blog post or some other source so that I can show these people that I'm not making this up when I tell them that sometimes lights make noise because they are made of hot metal?
Thanks for any help!

 

[robartsd]

You might look into ways to deflect the incoming cold air away from the fixtures. I imagine you've already done this, but be sure the bench focus of the fixtures is good to allow the fixtures to perform their best: not only will the light quaility be the best it can be, but the fixture will have the thermal loads distributed as they were designed to be.

 

[JD]

Heat cycle = noise, doesn't matter if it's a fixture or a wood stove! Only answer is to limit the heat with low temperature fixtures such as LED. If there is a specific fixture causing problems you may be able to find the exact part that is popping and make up a foil washer (if it's a screw) to limit it.

 

[BillConnerFASTC]

I was very aware of this with the pre-Shalespeare Altman axial, but not with Source 4 or even some of the more recent Strand profiles. Do you find this commonly on Source 4's?

I was sure when I saw title this was going to be about fans in LEDs, because we've observed (personally heard) problems with out of the box PL4 profiles and recently with a Phoenix LED - both of which I believe ship from the factory with fans at full which is not necessary for most theatre use, but maybe for display (constant) use in warm environments. Not sure how the Source 4 LED ships - fan at full or other.

 

[TheaterEd]

I have never heard a peep out of my S4s.

I also run a rig of par cans and s4 jrs in a black box that I have never observed popping. Tried to put some LEKO's in there and the lamp buzz was unbearable. Also, I can only use the cheapo LED's during loud musical numbers or summer shows when the AC units are running or else they are WAY too loud.

 

[derekleffew]

Wish I had a better answer for you @chilights . Question: do you normally have lots of cues/fades during these events? IIRC, with Altman 360Q, the clicking/ticking was most noticeable right after a fade up, regardless of how long the fixture had been on previously. You stated it happens no matter how much you preheat the fixtures. I fear the only solution is to change fixtures, or find a way to redirect the draft from the HVAC vents.

Yes, as TimMiller said, filament hum, more commonly called "lamp-sing," is a phenomenon of the SCR dimmer. Manufacturers have been struggling with this issue since the 1950s, and have rectified it [pun?] with the significantly more expensive sine-wave dimmer.

The "clicking" one hears from Altman 360Qs is expansion/contraction caused by heating/cooling of dissimilar materials (metals). Always useful in enhancing a quiet, dramatic moment in a play.

At least your problem isn't lamp sing, like this poster's: http://www.controlbooth.com/threads/buzzing-fixtures.28936/ .

 

[Les]

I am currently doing a show in a Shakespeare house, which I've worked in many times over the past decade and a half. Ever once in a while we hear a pop or two, but I wouldn't consider it excessive. I second the advice of checking fasteners, bench focus, etc. Hopefully the noise isn't something contacting the lamp because that should never happen.

Speaking of lamps, what wattage are you running? In the rare event that you're running FELs, it could be an overheat issue and on a similar note, lamping down to 575w may help if you're not there already.

As a side note, several of the Shakespeares where I'm working have been found to have cracked reflectors. You may want to check for that.

 

[carproelsofly]

Try backing off the knobs and screws on the offending fixtures by an eighth turn or so. It'll make it easier for the metal to move without vibration (sound).

That was our solution with the super-clicky 1KLs, and it worked like a charm.

HTH,
Jen