Film-Tech Forum ARCHIVE: Buzz in auditorium when striking lamp

This is topic Buzz in auditorium when striking lamp in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Tom Wienholt (Member # 1510) on 11-26-2010, 10:12 AM:

When striking the lamp, there is a "buzz" that is audible from all speakers in the auditorium. This booth was just installed. I assume this is a grounding issue?

Posted by Marin Zorica (Member # 1716) on 11-26-2010, 10:45 AM:

Probably the ground, cheak all ground wires and how the ground was made. Remember, ground should be made in that way that you have one star point, and all grounding to equipment (projectors, sound...) are wired from that point, with big conductors. Secound, even if that is okay, ground instlation could be bad, than you need someone to measure it for you. Also, if you using three phase, make sure sound rack is on diferent phase than ignitor on projector, that could help sometimes. Also bad capactirors in ignitor can cause this as well.

Posted by Mike Olpin (Member # 1115) on 11-26-2010, 10:50 AM:

Are your sound racks "piggybacked" onto your lamphouse?

Posted by Sam D. Chavez (Member # 1841) on 11-26-2010, 10:57 AM:

What brand lamphouse?

Posted by Tom Wienholt (Member # 1510) on 11-26-2010, 01:25 PM:

My sound rack sits about 3 feet away from the console. It is a Christie Xenolite 2000 watt console.

Posted by Sam D. Chavez (Member # 1841) on 11-26-2010, 02:16 PM:

You need to find out how the buzz is getting in.

What is the cinema processor?

Does the buzz go up and down with different fader settings?

Is the buzz getting in on one format and not the rest?

Digital, Non sync, etc.

Is the buzz in one channel or in all?

You get the idea.

Posted by Chris Slycord (Member # 4239) on 11-26-2010, 03:47 PM:

And does the buzz happen if the bulb is struck with the processor turned off (both with it cut off/running in bypass and with it entirely unplugged).

Posted by Jonathan Bodge (Member # 4072) on 11-26-2010, 05:08 PM:

I kinda like that sound, I know the movie is about to start.

Posted by Marin Zorica (Member # 1716) on 11-26-2010, 05:25 PM:

quote: Jonathan Bodge
I kinda like that sound, I know the movie is about to start.

Also some HF drivers like them, because it meant to kill em. I went to some cinemas, that sound was louder than any in movie what was playing that night in SRD.

Posted by Tom Wienholt (Member # 1510) on 11-27-2010, 12:33 AM:

The processor is a Dolby CP55. The buzz only happens when the lamp is striking (just for a split second) and seems to be coming from all channels in the auditorium (while in non-sync). I also noticed that the end cue triggers a very slight "click" that can be heard in the auditorium as well. I will check ground wiring first.

Posted by Sam D. Chavez (Member # 1841) on 11-27-2010, 12:49 AM:

I would unplug the non sync audio output wiring from the CP and see if it goes away. The shielding and wiring on most CD players is pretty sad and an easy way for the ignitor to penetrate.

The idea is to figure out the limits of the problem and then bore in on it.

Posted by Steve Guttag (Member # 268) on 11-27-2010, 01:15 AM:

Christie lamphouses/consoles excite grounding issues since they actually ground the negative side. Most all others float both sides.

Grounding is a tricky thing...it not only has to be there and be good but also one has to pay attention to the path noise has to take to avoid showing up in sound systems.

-Steve