Film-Tech Forum ARCHIVE: Sound issue on a Smart Mod VII

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Posted by Chris Iacofano (Member # 5074) on 02-08-2010, 10:52 PM:

I'm running a Smart MOD VII processor in Dolby SR in one of my theaters and I've noticed a strange problem. When dialogue is spoken there is a strange static sound that is barely noticeable. The static usually lasts for a split second after the spoken dialogue ends. I first noticed it several months ago, but have yet to hear a patron complain (my theater is in a college town with a film program, so trust me they do complain about these sort of things).

The thing is, this static only happens when dialogue is spoken in a particular pitch. Typically, it's characters that speak in a pitch that is in the lower registers of female voices and in the upper registers of a male voice. All other dialogue sounds fine, and I don't hear this (or it isn't as noticeable to me) in the rest of the sound mix.

Most recently I noticed this in a print of Red Cliff. I ran it in the other two auditoriums (one with an UltraStereo Js-200, one with a Dolby CP-500) and the static wasn't there. Could this be an alignment issue with the soundhead, or possibly something in the processor? Maybe the center channel speaker is going bad? What is the best way to troubleshoot this problem? Am I just being anal-retentive about things?

Posted by Monte L Fullmer (Member # 2797) on 02-09-2010, 01:29 AM:

almost sounds like the HF driver aluminum diaphram for the center speaker horn has started to crack on you...since it's not in the other channels..

Posted by Demetris Thoupis (Member # 833) on 02-09-2010, 01:40 AM:

These could be several things. I would first suggest changing (or exchanging) the High Frequency driver from the left to the centre speaker and see if you still get this static. SmartDev is not the best of processors. Does this happen in Analogue only? Do you have a Digital playback device like a DTS or a DA20?
Good Luck
Demetris

Posted by Jim Cassedy (Member # 4115) on 02-09-2010, 04:02 AM:

I had a similar problem last year and in my case
it turned out to be a bad active crossover module in
one of the large auditoriums where we bi-amp the sound.

I wish I had tried swapping the plug-in x-over mods
before I'd climbed all the way up some shakey scaffolding
backstage to replace the High Freq diaphram, which in
my case turned out not to be the problem.

The HF diaphram is usually the most likely cause for
the problem you describe, but if you can try swapping
anything else before you have to climb up and dis-
assemble your HF horn, you might want to give it a try.

Posted by Demetris Thoupis (Member # 833) on 02-09-2010, 06:41 AM:

A simple swap of the centre with the left channel amp will show indicate better if the problem is on the drive.

Posted by Sean McKinnon (Member # 612) on 02-09-2010, 12:59 PM:

The best advice I ever learned was that when it comes to sound problems the first place to always start even if you don't think it is where the problem is coming from is to perform an A chain alignment. Mis-Aligned optics/improper input levels can manifest in many strange ways that you wouldnt realize at first is coming from there. Also, once you rule it out yo know it's good and can move on down the line. I find starting at the begenning of a system and working my way through linearly works a lot better than guessing and jumping around all over the place.

Posted by Chris Iacofano (Member # 5074) on 02-09-2010, 07:54 PM:

Thanks for the advice everyone. As it turns out, it was the HF driver. Luckily it's pretty easy to access in that theater, so it was the first thing I checked.

I'm no fan of the Smart processors either, but it'll be gone in a couple of months when we install a CP650, so I'll just have to live with it in the meantime.