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TOPIC: Problems with sound

Problems with sound 08 Jun 2004 21:56 #21912

  • puzzlegut
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On Monday, we started to experience problems with the sound in one of our auditoriums. When the film would play, there would be a buzzing staticy sound. If there was music in the background of the movie, you couldn't really hear the buzzing. The buzzing is not very loud, but people can notice it during the quieter parts of the film. We tried running 2 different movies and they both have the same problem.

Does anyone have any suggestions as to what the problem may be? Where should we check? We've already looked at the wiring in the projection booth.
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Re: Problems with sound 08 Jun 2004 22:17 #21913

  • outaframe
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You didn't say whether this is an optical, or digital sound problem, but ASSUMING it's optical, AND you have already inspected the wiring, I'd inspect and "tap" all the soldered connections around the solar cell, and pull and clean off all the plugs and sockets leading to the preamp/processor and amps with electrical contact cleaner (with system turned OFF)... If you don't find a problem there, is there a possibility that someone bumped the projector sound lens or solar cell allignment which would lead to "motorboating" (reading sprocket holes instead of only the soundtrack)... ALSO inspect to be sure someone did not "sprocket run" (series of sprocket marks in soundtrack) the print, which causes the same kind of problem... Another possibility is "dirty" fader potentiometer (volume control)...
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Re: Problems with sound 08 Jun 2004 22:18 #21914

  • rodeojack
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Have you installed a lighting dimmer anywhere near the sound equipment recently?... maybe for your work area?

Outaframe has the rest pretty well covered. If you're not digital, I'd also vote that you're probably picking up a little DTS time code.

[This message has been edited by rodeojack (edited June 08, 2004).]
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Re: Problems with sound 08 Jun 2004 23:33 #21915

  • Ken Layton
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Are you using a Jaxlite or exciter lamp?
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Re: Problems with sound 09 Jun 2004 08:21 #21916

If you are using an exciter lamp or a Jaxlite replacement sometimes the lamp holder can vibrate or get pulled out enough to shift the focus of the lamp off the soundtrack and on to the frame lines or as someone pointed out already the sprocket holes. It remains intact enough to maintain electrical contact. If you have stereo one channel will be gone or have the noise in it.
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Re: Problems with sound 09 Jun 2004 09:12 #21917

  • puzzlegut
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Thanks for all the help. I cannot answer all of your questions since I'm not very technical when it comes to the projection equipment; my partner is the one that deals in that area.

We don't have digital sound. It shouldn't be the framing of the film since it has happened during each showing on Monday and Tuesday. We ran 2 different movies through the projector and both faced the same problem. The dimmer switch is near the sound switch, but it has been there since we bought the theater over a year ago.

If it also helps, we have the red light that reads the soundtrack. Also, whenever the furnice in that auditorium would kick on, it would make the sound worse.
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Re: Problems with sound 09 Jun 2004 10:03 #21918

  • jimor
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Your partner, who is the "technical one," may also have to test the internal electronics for a now perforated capacitor which may defeat the isolation of the sound amps from the 60hz AC line, which would pick up some of the 'hum' or buzzing-like sound you hear. He will probably know about this need, if the other mentioned sources of noise are eliminated. Let's hope it is a simpler cause (could someone have significantly disturbed the sound wiring in the walls or attic?), because circuit work is tedious and requires a lot of electronics knowledge. I hope you can get the schematics for your sound equipment.
Jim R. (new E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it ) member: www.HistoricTheatres.org
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Re: Problems with sound 09 Jun 2004 13:57 #21919

  • outaframe
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Hmmmmm, well now you are talking about two seperate problems which may or may NOT be related... The fact that the heating system causes noise in your sound system suggests that they are likely on the same electrical circuit (AC power line) which is a very BAD idea... The sound system should be on its own seperate circuit to help eliminate the possibility that something else on that circuit would introduce noise in the line which could show up in the sound... JIMOR's mention of 60 Hz hum is certainly correct, as well, but it's likely that that would have been present all along, and not just show up suddenly out of the blue... As he said, a capacitor failure COULD cause that, but its MORE likely to be either a poor ground issue, or a ground loop in the system that has been there since it was installed... Red light readers have a poorer signal-to-noise ratio than a standard white light reader, meaning they have a lower signal output which requires that it be ampified more (ALONG with any noise they may pick up) and adds to the vulnerability to external noise showing up in your system...

You also do NOT mention if the noise appears on ALL channels, or just in one channel (the center "dialogue" for instance)... IF its in the WHOLE system, that suggests that it could originate from the solar cell connections, or allignment, OR from the print itself (sprocket run, etc), OR from the preamp/processor before it goes through the seperate channel amplifiers into the speakers... You would need to have someone downstairs next to the speaker(s) listening as you disconnect each link of the chain (with the power OFF) to eliminate each component IN THE ORDER it feeds into the system... You will also need to first identify whether this is a "hum" you're hearing, or something more along the line of "static"... The hum suggests grounding problems, or less likely an open capacitor, but the static suggests a poor, or intermittent electrical connection somewhere it the signal path, and might also be a failing capacitor or resistor, or even a defective transistor in the preamp/processor chain...

IF the noise is in only ONE channel, that narrows it down to originating somewhere within the preamp/processor itself (noisy, dirty output level potentiometer?), OR plugs/jacks/wiring feeding that channel's amplifier, the amp's input level potentiometer (IF any), a problem within the amp itself, poor connection to the speaker lines (NOT likely), or even that the speaker(s) in that channel have a problem (poor connection at the speaker, diaphram failing in the HF horn, cone buzz or rubbing in the woofer, etc)...

Essentially, you have to first identify what the type of noise is you're hearing (hum, static, or distortion), then start eliminating links in the sound chain from A to Z as they produce sound in that order... ALWAYS eliminate the easy stuff FIRST, and assume that it's something simple: a headache is NOT usually a brain tumor!...

You will probably have to bring your technical partner into this, because it CAN get technical in a hurry, but given enough info, we can probably help locate your problem...



[This message has been edited by outaframe (edited June 09, 2004).]
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Re: Problems with sound 09 Jun 2004 18:23 #21920

  • rodeojack
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Jimor and Outaframe bring up good points, though I wouldn't be so quick to focus on that electrical leg. There's likely (& normal) to be a whole lot of stuff on the same power leg as the amplifier. The fact that the equipment is on the other side of a circuit breaker won't eliminate any interference... and putting the audio on its own leg back to the transformer would probably cause a rather serious imbalance in the building's electrical load. In the end, everything traces back to two or three incoming legs, and most theatre equipment is designed to handle it ok.

The capacitor issue sounds possible, though I wouldn't think a whole lot would get across the power transformer. Still, that kind of bypassing is what those caps are there for.

Since it's analog, I'm leaning toward a grounding issue. It's entirely possible that nothing in the sound system has changed. Sometimes, it seems ground loops can crop up because you sneezed in the wrong direction.

Here's something that might be helpful...
When you can hear that buzz, take a piece of paper... like part of a business card, and put it between the film and the pickup cell. The sound will go out... but it would be interesting to know if the buzz also disappears. That might eliminate some parts of the system & help narrow this down a bit.
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Re: Problems with sound 10 Jun 2004 09:07 #21921

  • puzzlegut
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I think we have the problem fixed. My partner changed the line amp in the projector and the buzzing noise stopped. But what is strange about it is that when we put the problem line amp in another projector, we didn't notice the same problem.
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Re: Problems with sound 10 Jun 2004 09:45 #21922

  • John Pytlak
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Sounds like you may have had a ground loop that was corrected in changing the connections on the amplifiers.

John P. Pytlak, Senior Technical Specialist
Customer Technical Services
Entertainment Imaging
Research Labs, Building 69, Room 7525A
Eastman Kodak Company
Rochester, NY 14650-1922
Telephone: +1 585-477-5325 Cell: +1 585-781-4036 Fax: +1 585-722-7243
E-Mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Website: http://www.kodak.com/go/motion
John P. Pytlak, Senior Technical Specialist
Customer Technical Services
Entertainment Imaging
Research Labs, Building 69, Room 7525A
Eastman Kodak Company
Rochester, NY 14650-1922
Telephone: +1 585-477-5325 Fax: +1 585-722-7243
E-Mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Website: http://www.kodak.com/go/motion
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Re: Problems with sound 10 Jun 2004 09:50 #21923

  • John Pytlak
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Some links to general information about solving "ground loop" problems:
http://www.epanorama.net/documents/groundloop/index.html
http://www.lh-electric.4t.com/gnd_loop.htm
http://www.dself.dsl.pipex.com/ampins/groundloops/grndloop.htm



John P. Pytlak, Senior Technical Specialist
Customer Technical Services
Entertainment Imaging
Research Labs, Building 69, Room 7525A
Eastman Kodak Company
Rochester, NY 14650-1922
Telephone: +1 585-477-5325 Cell: +1 585-781-4036 Fax: +1 585-722-7243
E-Mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Website: http://www.kodak.com/go/motion
John P. Pytlak, Senior Technical Specialist
Customer Technical Services
Entertainment Imaging
Research Labs, Building 69, Room 7525A
Eastman Kodak Company
Rochester, NY 14650-1922
Telephone: +1 585-477-5325 Fax: +1 585-722-7243
E-Mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Website: http://www.kodak.com/go/motion
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Re: Problems with sound 10 Jun 2004 12:44 #21924

  • outaframe
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Glad your problem is fixed... As John said, it could be that you corrected a ground loop in the process, or perhaps a faulty or resistive connection... Some of these things are very touchy...
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Re: Problems with sound 10 Jun 2004 13:12 #21925

  • jimor
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Ah, yes, outaframe, the possibility of a "resistive connection" sometimes called an 'intermittant.' The proverbial intermittant -- regardless of origin or cause -- is the bugaboo of any technician's life = a cause of major headaches and premature retirements! It was one of the things that got me out of repairing TVs and VCRs; toooo many ways cheap design/manufacture could cause intermittants and no profitability in trying to find them!! May puzzlegut's life and everyone else's here be free of intermittants in all equipment. Amen!
Jim R. (new E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it ) member: www.HistoricTheatres.org
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Re: Problems with sound 10 Jun 2004 22:53 #21926

  • rodeojack
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It's also amazing how many diodes you find around AM transmitters!
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