8mm Forum: Wow & Flutter

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Topic: Wow & Flutter

Terry Sills
Phenomenal Film Handler

Posts: 1423
From: Weymouth,Dorset,England
Registered: Oct 2012

posted January 18, 2016 02:22 PM

Just bought an IMac Bisonix in lovely virtually unused condition but on testing it with film the sound suffered from what I believe is known as 'wow'. That is to say there was a variation of speed that caused the sound to do the same. My first thought was lack of lubrication due to the machine not having been used for many years but everything looked well greased. Then I thought that maybe the flywheel was not running freely, but that seemed fine. I cleaned the drive belt in case that was slipping. Then after watching the mechanism running I noticed that there was a slight imperfection in the belt which as it ran over the motor pulley caused the slight variation of speed that was the cause of the problem. Changed the belt and now it's fine.
Just goes to show - check out the simple things first!

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Andrew Woodcock
Film God

Posts: 7477
From: Manchester Uk
Registered: Aug 2012

posted January 18, 2016 03:09 PM

It's good Terry when Wow or Flutter can be completely eradicated as simply as this.

It's certainly not always possible, just from a projectors inherent design in some cases.

Well done Terry! [Wink]

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"C'mon Baggy..Get with the beat"

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Brad Kimball
Phenomenal Film Handler

Posts: 1171
From: Highland Mills, NY USA
Registered: Jun 2003

posted October 30, 2019 08:46 PM

Is flutter when the sound is similar to someone talking under water? My Chinon 7000MV is sounds like someone’s gargling

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Claus Harding
Phenomenal Film Handler

Posts: 1149
From: Washington DC
Registered: Oct 2006

posted October 31, 2019 01:10 AM

"Wow" is the term for slow variations in speed, giving piano and orchestral passages the slow up-and-down pitch variations, much like when you reach the last grooves of an off-center LP.

"Flutter" is the fast variations in pitch, giving a vibrato-like quality to held notes.

Brad, your problem could be an issue of loops not being right, resulting in the film vibrating when it gets to the sound head.

Typically, a W/F factor of 0.2 off the speed is about where the ear really starts noticing; a good turntable or reel-to-reel will have a value of maybe 0.04 or so, resulting in rock-steady notes.
Most film projectors we use could never get to that level, but, as always, some are better than others. If your machine is fly-wheel dependent, running it for a few minutes prior to screening will help get the flywheel up to speed and give you more even sound. This is based on my Elmo St-1200.

C.

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"Why are there shots of deserts in a scene that's supposed to take place in Belgium during the winter?" (Review of 'Battle of the Bulge'.)

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Leonard Goss
Film Handler

Posts: 33
From: Launceston, Cornwall, UK.
Registered: Jul 2012

posted October 31, 2019 06:16 AM

Great projector the Imac Bisonix, I have one myself. Ingenious gauge change mechanism for a dual gauge sound projector with a single lever doing everything including switching the sound heads.

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A fan of 8mm movies since the mid 1960s and still as keen as ever!

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Brad Kimball
Phenomenal Film Handler

Posts: 1171
From: Highland Mills, NY USA
Registered: Jun 2003

posted October 31, 2019 08:34 AM

Claus, would replacing the belt help? The unit runs fine otherwise. It just all sounds like someone’s gargling while talking or instruments filled with water.

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Claus Harding
Phenomenal Film Handler

Posts: 1149
From: Washington DC
Registered: Oct 2006

posted October 31, 2019 09:33 AM

I don't know if that would solve it. Keep in mind that the film needs to be "done" with its staccato rhythm from the lower loop and be running smoothly by the time it reaches the sound head/drum. If the loop formers aren't adjusted right, you can get the kind of fast-pitched disturbance you described. I have had that happen on one of my 16mm machines.

C.

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"Why are there shots of deserts in a scene that's supposed to take place in Belgium during the winter?" (Review of 'Battle of the Bulge'.)

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Paul Adsett
Film God

Posts: 5003
From: USA
Registered: Jun 2003

posted October 31, 2019 09:39 AM

Wow and flutter are definitely influenced by projector design and film properties. Some projectors, like Elmo's, seem to be more susceptible to wow with certain films than others. Eumig's never seem to exhibit these problems in any of their projector models. A lot of it is related to the particular design of the sound capstan and pressure roller. And a slippery film, due to too much lubrication, is really going to aggravate the problem.

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The best of all worlds- 8mm, super 8mm, 9.5mm, and HD Digital Projection,
Elmo GS1200 f1.0 2-blade
Eumig S938 Stereo f1.0 Ektar
Panasonic PT-AE4000U digital pj

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