Film-Tech Forum ARCHIVE: Crackling

This is topic Crackling in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Jeremy M Smith (Member # 4913) on 07-16-2012, 08:48 PM:

Just wandering if anyone has had this problem.

In one of my cinemas a have a Crackling noise coming from the center and more so from the right channel. It will only do if with some prints ie Spider Man is fine TED is not but TED is fine in another cinema that has the same sound head. We have had a tech look at it twice also.

Thanks
Jeremy

Posted by Randy Stankey (Member # 64) on 07-16-2012, 09:36 PM:

It could come from a scratched soundtrack.
It could be because of a misaligned A-chain or something wrong in the processor.
It could be a bad amp or a bad speaker.

The difference between movies could be because of a problem with the print. (e.g. The above-mentioned soundtrack.) It could also be because of the way the movie is mixed but it could also be a coincidence.

What projector/sound head are you using?
What sound processor are you using?

Are you playing any or all of the prints in digital? (Dolby Digital or DTS?)

The difference between the sound quality of different prints could be because one is playing in digital but the other isn't. In that case, you would need to perform a complete tune-up on both the analog/optical A-Chain and the digital reader alignments.

While you've got the equipment out (or while you have a technician on-site) you could do a complete A-chain alignment, a digital alignment and a B-chain EQ.

Since we are now in an era dominated by digital projection, it would serve you well to have your film projector working as well as you possibly can. The smart move would be to call a technician and have him tune the whole system.

Posted by Monte L Fullmer (Member # 2797) on 07-18-2012, 12:53 PM:

I called it a cracked diaphram in the horn driver.

They're made of very thin aluminum if any low frequencies went to the horn, it will take out a diaphram in a quick. But age itself can cause diaphram cracking.

The cracks are created at the base of the dome of the diaphram-very hairline cracks to noticable ones. One can check this out by taking off the rear cover of the driver to inspect the diaphram itself.

They're easy to change out-just follow polarity, but a tech is your best bet to find out the problem.

Common issue is older cinemas having speakers set for low wattage amplifiers (the Altec/Lansing "Voice of the Theatre" - A4, A7 - speakers are a good example: a transistor radio can drive these speakers and make that radio sound great) and when that cinema do a digital sound conversion with higher wattage amplifiers, this setup will easily create horn problems.