8mm Forum: Wow & Flutter

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Posted by Terry Sills (Member # 3309) on 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!

Posted by Andrew Woodcock (Member # 3260) on 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]

Posted by Brad Kimball (Member # 5) on 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

Posted by Claus Harding (Member # 702) on 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.

Posted by Leonard Goss (Member # 3172) on 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.

Posted by Brad Kimball (Member # 5) on 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.

Posted by Claus Harding (Member # 702) on 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.

Posted by Paul Adsett (Member # 25) on 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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