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Author
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Topic: Help with a sound problem
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John Pytlak
Film God
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Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 11-08-2000 12:24 PM
I suspect the film is "wandering" side-to-side on the analog sound drum, allowing the perforations to be scanned. Standard SMPTE 203 specifies track 1 (left channel) is on the inboard side, and track 2 (right channel) is on the outboard (perforation) side, so it sounds like the film perforations are occasionally wandering into the scanned area for track 2, giving the "motorboat" sound on the right and (derived) center channel. The audio frequency the perfs make is 96pps (putts per second). (24fps x 4 = 96). ![](http://216.97.28.234/ubb/wink.gif) Since you said that the problem is not confined to one print, or section of a print, and sometimes goes away when you rethread the soundhead, I suspect that the tensioning and postition of the film as it goes around the sound drum is incorrect. If you can provide the model number of the soundhead, I'm sure others more familiar with it can guide you on checking proper tension and alignment. ------------------ John P. Pytlak, Senior Technical Specialist Worldwide Technical Services, Entertainment Imaging Eastman Kodak Company Research Labs, Building 69, Room 7419 Rochester, New York, 14650-1922 USA Tel: 716-477-5325 Fax: 716-722-7243 E-Mail: john.pytlak@kodak.com
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Matt Ashburn
Film Handler
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Posts: 16
From: Martinsville, Virginia, USA
Registered: Aug 2000
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posted 11-08-2000 01:36 PM
I'm not sure if this would apply, as this problem was experienced on some Century projectors this past summer.The problem on the Centurys was that the tension around the sound mecahnisms was too taunt, causing a sound that was described as a "train running" or a "lawnmower." Relieving some tension by squeezing together the rollers surrounding the drum or by rethreading solved this problem. Here's a diagram: Like I said, I'm not sure if it applies to your setup, but I thought I'd throw it out for you. Matt Ashburn, Hollywood Cinema Martinsville, VA
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Rick Long
Jedi Master Film Handler
Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999
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posted 11-08-2000 09:47 PM
The intemittancy of this problem reminds me of a tip from the old Simplex sound-head manuals. When you close the guide rollers over the drum, the assembly is held there by a small pin under the sound drum. If this pin is allowed to become dry, it can impeade the rollers from springing back out to their proper position. A small drop of oil on this pin will alleviate that problem. Presumably this thing was once operating properly, so I do not recommend adjusting the lateral guide adjustment unless you have a good loop of Buzz-track, and know how to use it.
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John Walsh
Film God
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Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999
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posted 11-09-2000 10:49 AM
I think Bill was just trying to provide a quick fix (by suggesting to steal a washer from the soundhead door.) Easily avaiable, and free! Any washer can be used to replace the stolen one.Off hand, I don't know what the standard thickness for washers is, but if it's not 0.025" it can be a bit expensive to have made. We've had a problem like this for quite awhile that no one has been able to figure out... A buzzing sound (like a 60hz hum); happens on some, but not all Five Star soundheads; most prints are OK- happens only on a few; pushing the film over can make it go away, but when alignment film is run, it tests OK. Our projectors were shipped about six years ago-- could this be part of that "short standoff" batch? If this is our problem, I'm gonna be a happy camper!
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Bill Purdy
Expert Film Handler
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Posts: 139
From: Seattle, WA
Registered: Oct 1999
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posted 11-10-2000 09:57 AM
I just grabbed a pair of dial calipers and looked at 0.025". Not enough, so, I guess I misled you. It needs to be more and that washer I suggested you "borrow" is thicker than normal which is why it works so well. For those who would like to pursue this further, the first thing to check is the sharpness of the flanges on a roller that has been in there for awhile. The aluminum is soft and wears easily, so one which is out of line will develop a sharp flange. To really prove the point you need to make a guage. If you have the facilities to make it yourself, or if you can get a machinist to make it for you, you need a piece of metal (preferably brass or aluminum) which is 0.330" thick. This is the distance from the outboard edge of the sound drum to the outboard edge of the film. You lay your gauge across the end of the sound drum and gently slide it until it touches the inner flange of the lateral guide roller. The inner flange (the one which determines film position) should just kiss the guage. If you have made your guage long enough, you then slide it up until it touches the aluminum roller and it should also line up. So, where does this 0.330" come from? When we were doing our original design work on our sound readers we wanted to know just where the film wanted to run. In other words, where was the original design point? After measuring numerous lens mounts we were able to get a pretty consistent number. This was confirmed (within 0.004") by Rick Sanjurjo at Ballantyne who started with the drawings for the picture head and traced the film center line down to the sound drum. To be sure, there can be variations in the tolerances of the sound drum itself (although, LaVezzi is mighty good) and the machining of the bearing seats in the sound head casting, but they are really pretty close. At least, this gives you a starting point. ------------------ Bill Purdy Component Engineering
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