Film-Tech Forum ARCHIVE: Unsteady Sound

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Posted by Brian D. Nelson (Member # 3277) on 08-13-2005, 03:29 PM:

In the last few months I've had the sound start to get unsteady but without consistancy, almost like a fluterring in and out. If it happens, it's usually after mid point through the 6000 foot reel, in the second to third shipping reel right through to end. I had encountered this before when there was specks of accumulated shed material (and other junk missed) found on the sound drum of the Century (Model R5B), which I cleaned and the problem was solved. I make sure I check those drums every day now so I'm quite sure that isn't the cause this time. The drum rotates smoothly and easily, the film seems to be fed consistantly and smoothly as well.

I had considered that maybe the drive belt on the take-up might be too tight, but there's just enough slip to not add too much tension and the sprocket checks out as well. The next consideration was the focus of the Reader (JAX, yeah I know, I'm working on upgrading very soon). Is that a reasonable concern?

Posted by Peter Mork (Member # 1336) on 08-13-2005, 03:55 PM:

Be sure there's some slack on the film going arounf the sound drum. You may have threaded it that way, but a faulty or misadjusted pad roller on the sprocket that pulls film through the head could cause it to slip and pull the film tight, which would make a difference you can hear.

I doubt it has anything to do with the reader.

Posted by Brian D. Nelson (Member # 3277) on 08-13-2005, 04:00 PM:

Ah, like if there's too much sudden pull from the take-up causing the the film to jump a tooth or two on the sprocket which pulls the film tight. I've had that happen before and indeed experienced that issue with the sound being affected. Unfortunately, that isn't the case this time, there's still slack in either way.

Posted by Gordon McLeod (Member # 33) on 08-13-2005, 04:18 PM:

First Peter is incorrect there must be no slack in the threading of the soundhead a century is a davis tight loop
Check the roller on the kelmar arm I have had those get elipictal and wooble transitiing it back into the centuy soundhead
Also check the felt clutchs and aluminum plate on the take up

Posted by Brian D. Nelson (Member # 3277) on 08-13-2005, 04:33 PM:

Thanks Gordon, that seems the most likely. I just had a closer look at that roller, it does appear to have a slight elipictal shape, time for a new one. I also noted that there seems to be less play in the action of the that lower arm which now needs attention.

When I took this old theater over with aged equipment, it became obvious that the previous operator didn't pay much attention (or money for Tech time) to the equipment so I'm having to learn and fix as I go.

Posted by Brad Miller (Member # 2) on 08-13-2005, 05:48 PM:

Make a loop of a trailer with a stretch of music in it that would show off wow and flutter and run it for an hour non-stop. Does the problem still appear? That will isolate whether it has something to do with the extra stress from the takeup or something in the soundhead.

BTW, if you thread a Century soundhead with slack, provided the bearings are in good condition you still won't have wow or flutter (except possibly at splices). In fact it's a good quick test. [Wink]

Also, have you checked the damping fluid? Most people forget about that.

Posted by Sam D. Chavez (Member # 1841) on 08-13-2005, 06:07 PM:

You should determine whether the upper and lower rollers around the sound drum that form the Davis loop, float to the middle of their travel as soon as the sound drum comes up to speed. If they don't it usually means dragging bearings in the sound drum.

If the two rollers jump up and down when the projector is running it usually means the projector is beating itself to death as in bad shutter bearings or gears.

As to Brad's suggetsion that you run a loop for an hour, this will only work if you put a weighted roller on the film loop as it coes out the bottom of the sound head. Century's lose the loop all day long and now with Estar film, it's a good way to have the film wrap around the bottom sprocket and break something important for sure.

Posted by Brad Miller (Member # 2) on 08-13-2005, 06:12 PM:

quote: Sam D. Chavez
Century's lose the loop all day long and now with Estar film

What??? I've yet to have that problem and I have been guilty of leaving a loop running for a looong time. Maybe I am setting the pad roller clearance differently or I make my splices different than you do. Is this really a widespread problem people have when running loops on a Century soundhead? [Confused]

Posted by Brian D. Nelson (Member # 3277) on 08-13-2005, 10:40 PM:

quote: Brad Miller
Is this really a widespread problem people have when running loops on a Century soundhead?

One of the projectionists I had working for me last year had that happen with a loop of test tape. It jammed around the sprocket and locked the whole works to dead stop, doing damage to the main drive motor before the breaker flipped. Fortunately, it didn't damage anything of significance other than the motor and toothed drive belt.

Sam, the arms stay stable after the drum gets up to speed on both machines, I'll look for those symptoms in the future. Thanks for sharing the advice as I have a pair of Simplex XL's (model 1008) that I'm suspicious of, I have no idea if previous operators looked after them well at all. So far the picture is steady as runs quite quietly.

Brad and Gordon, thanks to you aswell. It seems it was the roller on the lower arm being out of shape and transmitting movement up the film. I changed it (had a new one in the odd storage of spare parts) and now the sound is steady. Out of interest and future consideration, roughly how much tension should be present before the take-up clutch allows slip?

Also, I did not know about the damping fluid. I think what I really need to do is read a copy of the operating manual (of which I don't have). Is there one listed in the "Manuals" section that is applicable?

Posted by Michael Schaffer (Member # 1204) on 08-13-2005, 11:04 PM:

quote: Brian D. Nelson
Fortunately, it didn't damage anything of significance other than the motor and toothed drive belt.

And a motor is only $350 or so, so who cares [thumbsup]

Posted by Brian D. Nelson (Member # 3277) on 08-13-2005, 11:10 PM:

quote: Michael Schaffer
And a motor is only $350 or so, so who cares

Actually, it only cost $75.00 to get it fixed and runs just fine. Note, I said "...other than the motor and the toothed drive belt." It could have been a lot worse for that lesson learned.

Posted by Daryl C. W. O'Shea (Member # 1303) on 08-14-2005, 06:03 AM:

quote: Brad Miller
What??? I've yet to have that problem and I have been guilty of leaving a loop running for a looong time. Maybe I am setting the pad roller clearance differently or I make my splices different than you do. Is this really a widespread problem people have when running loops on a Century soundhead?

Pad roller clearance doesn't even come into play. The film gets spit outwards to the left starting almost from the bottom of the sprocket (below the pad roller). I find projection angle affects most whether it will loose the loop or not. The greater a -ve angle the less it will happen. It almost always happens with a +ve angle.

If I don't have a weighted roller handy, and it won't keep the loop, I'll often thread straight down between the pad roller and the sprocket. It only contacts ~2 teeth on each side that way, but when you're in a pinch...

Posted by Brad Miller (Member # 2) on 08-14-2005, 03:18 PM:

Are you guys threading around that last idler roller after the holdback sprocket? Don't.

Posted by Jon Miller (Member # 163) on 08-14-2005, 05:07 PM:

For clarification's sake...

So the green path should be followed, not the blue path? Or is it the other way around (as I've been doing for years)?

Posted by Sam D. Chavez (Member # 1841) on 08-14-2005, 05:36 PM:

If you do not thread around the idler roller, you have something like one tooth holding the film. It will lose the tension more often than not and as a sound guy I'm not into fooling around with someone elses pad rollers unless I really need to.

The better way in my opinion is to go around the idler roller so you have some wrap around the sprocket. I use a weighted roller to keep the film from wrapping.

Posted by Steve Guttag (Member # 268) on 08-14-2005, 05:56 PM:

I have generally found that if I use my finger to hold the film on the hold back sprocket until the tension rollers settle, it will run indefinately after that (using the idler roller).

As to the tensioners dancing, another cause is the older style rubbler coupling on the Direct Drive models swelling up (CG-629, if I recall). Check the coupling regularly to avoid that problem.

[ 08-15-2005, 04:59 PM: Message edited by: Steve Guttag ]

Posted by Gordon McLeod (Member # 33) on 08-14-2005, 06:45 PM:

If you don't go around the roller you have as same mentioned only one perf or two engageing the film
If you let the film run slack I have seen the sound drum scratch up prints Davis new what he was doing when he designed it so I recomend following it

Posted by Sam D. Chavez (Member # 1841) on 08-15-2005, 11:12 AM:

Yech, Century Direct drive. Another wonderful innovation run on a speedometer cable barely big enough to run the soundhead, much less the 6000 Ft, and 70mm reels prevalent in those days.

Posted by Gordon McLeod (Member # 33) on 08-15-2005, 11:46 AM:

The original R2 soundhead was a direct drive system as well back in the 40's as part of the "master soundsystem"