Film-Tech Forum ARCHIVE: How do I get rid of "Whirr"

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Posted by Andrew Bangs (Member # 4938) on 09-21-2008, 02:53 PM:

I have been having a horrible time with this whirring sound in one of our theatres. After aligning the sound head as best as I can I came to the conclusion that the "whirr" is primarily in the Left sound track. Which means to me it is not picking up sprocket holes (which is what my coworker suggested.) I have now adjusted the beam to the far out side of the sound track practically eliminating the left sound feed and the noise is practically gone. However I am now left with a theatre that has no left channel and most of the sound comes from the right. Fairly unnerving. Is their something else besides alignment that could cause the "whirring" noise? One thing that worries me is the cover for the circuit board of the camera is missing and has been ever since I started working here. How can I safely clean this out to remove the possibility of dirt their causing the problem? Mind you I have cleaned the sound head very gently with alcohol and a Q-Tip. So I do not believe dirt there is the issue. But at this point I will probably try anything. I have also pleaded for an actual tech which I am sure is what the real solution should be. However in the mean time I still feel I need to do something.

Thanks in advance for the help.

Posted by Gordon McLeod (Member # 33) on 09-21-2008, 03:42 PM:

Is there a loss of high frequencies if so the focus could be off causing a magnification error

Posted by Mark Gulbrandsen (Member # 72) on 09-21-2008, 07:29 PM:

If it sounds like a radial airplane engine you're scanning the DTS track. You need a loop of Buzz track to properly set the lateral position.

Mark

Posted by John Wilson (Member # 269) on 09-21-2008, 09:42 PM:

Indeed...left channel would be the DTS time code track.

Posted by Richard Hamilton (Member # 321) on 09-23-2008, 10:04 AM:

Andrew,
Seems like your having alot of trouble with these Chinese projectors [Eek!]

If I remember correctly, I think I spent a day in Kerrville with the engineers from Harbin working on the platters. They had a couple of issues, which I thought were straightened out at the factory. Although, your equipment was already in the states.

As far as your sound problems, my experience with the projectors was during the install, no problems. Sounds like you have an alignment problem.

Rick

Posted by Andrew Bangs (Member # 4938) on 09-23-2008, 01:03 PM:

quote: Richard Hamilton
If I remember correctly, I think I spent a day in Kerrville with the engineers from Harbin working on the platters. They had a couple of issues, which I thought were straightened out at the factory. Although, your equipment was already in the states.

Yep and since their visit we have had some more problems with the Platters. I'd say at least Half are down to two Working Platters and one is completely dead right now. It is great being the guinea Pigs for this equipment.

As far as aligning I so far have only looked at adjusting the beam source now I am starting to think it is the film tracking or the camera that is off.

Posted by Tony Bandiera Jr (Member # 2365) on 09-23-2008, 01:54 PM:

Andrew:

Soundhead alignment, analog or digital, is critical and not to be attempted by eye or ear (with the exception of Buzz track) and you're only making things worse by fiddling.

I will gladly send you some buzz track and instructions on how to use it, please send me a PM and I'll get that off to you.

Posted by David Boyd (Member # 4936) on 09-24-2008, 06:00 AM:

We had that problem with the beam being too wide. Depends on the design and setup of your sound head scanner. When you run the buzz if you get a buzz either way and can't get a silent bit in the middle then the beam is too wide. You might find this with some laser scanners. Best upgrade (own opinion from experience) is BACP.

David.

Posted by Mark Gulbrandsen (Member # 72) on 09-24-2008, 08:07 AM:

Actually Buzz SHOULD be done with a scope as well. Also it is possible to adjust the scanning width on some scanners in particuluar Cinemecanicca(spelling?) and the early Kelmar types.

Posted by Andrew Bangs (Member # 4938) on 09-24-2008, 09:56 AM:

Thank you all for all the wonderful tips and suggestions but I finally got it solved. And in the end It was something so simple I feel silly for not checking it earlier.

Their is a swinging Tension arm that straddles the sound roller and this had come lose shifting the film slightly off center. Once I tightened it back up so that the film ran straight the "whirr" was gone and I could re-align my beam so that all L,C,R, and surround tracks were clean and loud. In the future I will try not to get so Focused on a problem thinking they is only one place things go wrong. When in fact their are usually many. I will say it was some of the Suggestions given in this forum that got me thinking and looking in different places.

quote: Mark Gulbrandsen
If it sounds like a radial airplane engine you're scanning the DTS track.

This is what the problem was. I realized when I set the Beam offset to reduce the Left track that it was not picking up the space in the sprocket holes which is what I was told the problem was by an ex-coworker. (Listening to that idiot was my first major mistake) Then with the mention of the DTS Track I smacked my forehead and said of course! 5 min later after a quick adjustment everything was literally back on track.

quote: Tony Bandiera Jr
I will gladly send you some buzz track and instructions on how to use it

Thank you for the gracious offer and perhaps in the future I will take you up on this but for now everything is peachy. And hopefully I will have a tech coming soon anyways to fix some of our other problems. At which point I will be a parrot on his/her shoulder Learning any and everything I can. As well as asking some good questions.

So Cheers to you all! [beer]

Posted by Tony Bandiera Jr (Member # 2365) on 09-25-2008, 12:04 AM:

Glad to hear you got it working Andrew! Good job of troubleshooting.

And watching the tech when you get one there, and asking questions will help you learn a lot. It's how I got my start as a tech, a combination of reading every document I could get my hands on, and taking instruction from a great tech, Kent Peterson.

Big [thumbsup]

to you!!

Posted by Richard Fowler (Member # 893) on 09-25-2008, 01:45 PM:

The Harbin and other current Chinese projectors have sound drum guide rollers are based on a Meopta design. If the upper or lower guide roller is loose or the bar holding the both, you will have tracking problems.