Film-Tech Forum ARCHIVE: Strange "Bang" in speakers ?

This is topic Strange "Bang" in speakers ? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Henrik Sanden (Member # 1222) on 09-14-2002, 08:27 PM:

Hi!

We have a strange problem in two of our tree auditoriums. A stange "Bang" suddenly come from the right loudspeaker. often just one, but sometimes there is many after each other, like a thunderstorm. We have tried changed the amplifier but the problem is still there. What can it be ? Some moths ago the problem appeared rarley (Once a month... maybe) but not almost every day.

The "Thunder" is loud and low frq and can appear i any soundformat (SR/SRD/DTS). Running CP500 and CP650.

Posted by Matthew Bailey (Member # 601) on 09-14-2002, 09:26 PM:

It maight be the audio outs of your proceccors or something. Maybe the cables between them & the amplifiers. Something with ground perhaps? It's probably the noise created by any nearby switches or relays. Have any lighting,anything electronic or electrical in the theatre & booth checked to see what's making the noise.

Posted by Daryl C. W. O'Shea (Member # 1303) on 09-14-2002, 09:39 PM:

Check any soldered connections inside D-Sub shells. I've seen installations that work fine for years before a crappy soldering job starts causing static, noise, or just plain muting.

Posted by Darryl Spicer (Member # 711) on 09-15-2002, 12:03 AM:

Make sure that all conections are tight on the back of the main frame of the processor units. Especially the outputs going to the amps.

Posted by Paul G. Thompson (Member # 655) on 09-15-2002, 01:33 AM:

Henrik said:

quote:
"but sometimes there is many after each other, like a thunderstorm."

It sounds like it might be "motorboating."

High-Power amplifiers will make some strange noises if the input and output cables are run parallel, especially if they are all in the same bundle.

If you have this condition, separate the inputs from the outputs. Maintain the inputs on one side of the cabnet, and the outputs on the other side.

Posted by Pete Naples (Member # 761) on 09-15-2002, 05:45 AM:

Is this a CP500?
I've had Cat675's going west on me make all kinds of wierd noises as they fail, including what was described to me as gunfire and thunder. Check the CP's event log and the watchdog led's on the cards. It's often worth swapping the Cat675's from one slot to another, the two in the middle of the CP500 can be swapped easily, and will reconfigure themselves on power up. You can swap either of them with the third Cat675 in the DA20 sub section, but you have to move a jumper, as the cards are running at a different clock speed in the DA20 section.
Sorry if that's a bit vague, but it's Sunday morning and I'm still recovering from Saturday night!

Posted by Steve Guttag (Member # 268) on 09-15-2002, 11:09 AM:

>>"Hi!

I think you all missed a vital clue in the above...these are "TREE" auditoriums!!! The problems are after thunderstorms...the answer is obvious...the bangings are merely tree branches falling down as the tree ages!

(I just couldn't resist)

Steve

------------------
"Old projectionists never die, they just changeover!"

Posted by Henrik Sanden (Member # 1222) on 09-15-2002, 11:21 AM:

Thanks for your answers. I will check the cables that Paul mentioned. And i will also check the forest behind the screen

Posted by Bruce Hansen (Member # 281) on 09-15-2002, 06:27 PM:

This could be dirty connectors. Try reseating (and cleaning) the connectors. It could also be static, which would be getting worse now that fall has started, and the humidity is droping. Check for proper grounding of the audio gear, and the projector.

Posted by Paul G. Thompson (Member # 655) on 09-15-2002, 06:56 PM:

Henrik, if the people in Sweden drive like they do here, you might want to check if someone has not plowed their car into the side of your building.

Posted by Jon Bartow (Member # 241) on 09-15-2002, 07:59 PM:

I had the exact same thing at one of my theaters recently. Except in the Left surround channel only. Turned out to be the DAC card. cat 685. Replaced the card, no more custom special effects