Film-Tech Forum ARCHIVE: Help diagnose sound troubles?

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Posted by Derek Miner (Member # 2348) on 05-17-2004, 02:14 AM:

Had a couple sound issues tonight with no resolution. One is ongoing, and the other has happened before but is rare.

Both auditoriums I'm dealing with have the Ultra Stereo JS 5/95 and SDDS equipment. The booth monitor is the Ultra Stereo CM-80E. I'm not sure what the amps in the system are off the top of my head.

The problem that hasn't happened in a while is that the sound in one auditorium is suddenly lacking in low end - dialog is incredibly tinny. We happen to be running "Laws of Attraction" there, which has SDDS, but bypassing (or turning off) that unit makes no difference. On the booth monitor, there is a noticable difference in sound quality and level when switching between the Processor monitor and Amplifier monitor. I powered off all the amps and turned them back on again (hoping for the "Fonzie Effect" I suppose), which did not do anything. This auditorium was fine a few days ago, and the last time I noticed this sound problem was several months ago.

In the other auditorium, we are plagued with a wow and flutter in the sound, which occasionally develops a hum. This is constant, and has been for a month or two. The "solution" has been to put the UltraStereo 5/95 into "Bypass" to get rid of the noise. Upon further inspection, this does not eliminate the sound issues, it just folds all the sound to the front so it's not as noticable. Our head projectionist ruled out the LED analog track reader, saying the fluctuation wouldn't come from there. Since I can still hear the wow and flutter in Bypass, I'm ruling out the cards in the unit, and I'm making a guess that it's probably nothing to do with the piece of equipment at all. I haven't been able to play anything in here with SDDS, but Tuesday, I might grab a trailer with SDDS out of the cabinet and thread it up and see how it sounds.

Posted by Mark Gulbrandsen (Member # 72) on 05-17-2004, 07:46 AM:

1. "the sound in one auditorium is suddenly lacking in low end"

This is easy..... I ran a service call for this problem at one customers theatre last week... someone had turned the LF amp down. Damed level knobs on the front panel [Mad]

!!

You have lost the LF on the center channel . You should find one of these wrong... Woofer blown, LF amp turned down, bad LF amp, bad electronic or passive x-over(least likely), loose wires or connections.

2. "we are plagued with a wow and flutter in the sound, which occasionally develops a hum."

Another easy one.... and the clue is that you haven't played anything in digital, only analog. Digital should sound fine in this theatre.

More than likely bad bearings in the sound reproducer. Is this a 5 star sound head? Check the parts of the scanner very carefully... bearings might be bad in the rotary stabilizer, or the lateral guide roller(the one you close over the sound drum) bearings might be bad or the sprung roller half of the lateral guide may be stuck in the open position so the film is weaving back and forth in the scanning beam. The hum could be from the scanner picking up either the DTS track, frame lines or perferations depending on which way the film is weaving in the scanning beam and how far it is weaving.

If you can't find anything obvious call your tech in [thumbsup]

as a frozen sound drum can and will damage film.

Mark @ CLACO