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Topic: exciter sound problem

Patrick de Groot
Expert Film Handler

Posts: 161
From: Sprang-Capelle, Netherlands
Registered: Apr 2001

posted 06-05-2001 01:51 PM

We've got a problem with sound in our theater. When there is no film running through the projector and I put the exciter lamp on, you can hear a hum through the speakers. What can be the cause of this?

I don't hear it when the exciter lamp is off and all other equipment is on. I have already tried to dim the lights in the booth, but that didn't help...

Any ideas? Please help me out

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 06-05-2001 02:08 PM

The most likely cause is a poorly filtered power supply for the exciter lamp. Any AC (alternating current) ripple in the power supply will cause a hum in the sound when the exciter lamp is on. To verify the light output has ripple, block the light with a business card to see if the hum stops.

You might check to be sure the power supply is not in "bypass" or "emergency" mode, feeding AC to the exciter lamp rather than the pure DC (direct current) required.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 06-05-2001 02:40 PM

Did you recently do any upgrades or changes to your soundsystem such ad a subwoofer?
Some of the European machines used AC excitors with filters in the amps to eliminate the hum. Others used massive heavy filimented lamps to damp out the hum?

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Kyle Abel
Film Handler

Posts: 56
From: Plano, TX, USA
Registered: Apr 2001

posted 06-05-2001 03:28 PM

An obvious one, but make sure your processor is switching back to non-sync mode after film runs out.

------------------
Kyle Abel
General Manager
Plano Movies 10

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Demetris Thoupis
Phenomenal Film Handler

Posts: 1240
From: Aradippou, Larnaca, Cyprus
Registered: Apr 2001

posted 06-05-2001 04:04 PM

Hmm,
Another reason might be that the projector is not properly grounded (but if the humming sound is heard when projector motor is turned off then it probably is something else).

Demetris Thoupis

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Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

posted 06-05-2001 05:30 PM

Are you using a jax light exciter lamp red led for your sound source. If so these are notorious for picking up huming do to the fact that it needs a ground wire hooked to the negative lead on the power supply unit ore a ground wire hooked to the ground on the line amplifier for the solar cell that the jax light requires to boost the signal. you can rin a wire from the ground on this line amp to a screw on the sound head casing.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 06-05-2001 06:27 PM

Not all excitor supplies used in european machines will accept the grounding of one side of the powersupply

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Tom Kroening
Expert Film Handler

Posts: 214
From: Janesville, WI USA
Registered: Oct 1999

posted 06-05-2001 06:35 PM

We are having the same problem in one of our small auditoriums. Sometimes you can hear a buzz even when the movie is not playing. This seems to only be an intermittent problem. Even when you can't hear a buzz on screen you can hear one throug the monitor. For some reason the backup light is flashing on the monitor. Also, i noticed that you can hear a buzz from the exciter bulb itself. I reall havn't had the time to trouble shoot this problem yet, hopefully when we get some new exciter bulbs i'll take a closer look.

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Patrick de Groot
Expert Film Handler

Posts: 161
From: Sprang-Capelle, Netherlands
Registered: Apr 2001

posted 06-12-2001 12:54 PM

Sorry for my late reply, but I wanted to test it out.

It seems John is right. I've found another transformator and got the voltage and amp right. The humming sound disappears! However there is still another sound problem (yes, this is a problem auditorium...)

The sound is distorted. It isn't caused by the speakers because cd's play well. I think the cause lays in the a-chain, because the input levels on the mixer (...) are not entering the red area, but it still sounds like crap.

Once again, any ideas? It would be appreciated.

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 06-12-2001 01:00 PM

"I think the cause lays in the a-chain, because the input levels on the mixer (...) are not entering the red area, but it still sounds like crap."

Please explain this. A mixer??? If your theater is doing what I think is being done, I think the problem has just surfaced. Then again, perhaps the word "mixer" doesn't translate well into English.

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Patrick de Groot
Expert Film Handler

Posts: 161
From: Sprang-Capelle, Netherlands
Registered: Apr 2001

posted 06-12-2001 01:02 PM

I thought lets clear out "distorted" in the message above. The sound sounds like it's clipping. And it seems like the bass is to heavy and the treble to low.

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Patrick de Groot
Expert Film Handler

Posts: 161
From: Sprang-Capelle, Netherlands
Registered: Apr 2001

posted 06-12-2001 01:06 PM

well I keep replying

Mixer, jep, those things with some faders and knobs. That why I put those ... after the word.

We get reasonable good sound from them (using the MIC input's) in another auditorium. But of course I also wants some real cinema equipment like a Dolby or DTS processor. Well, my boss is thinking about it...

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 06-12-2001 09:05 PM

Patrick, has the sound always been bassy with mushy treble? First thing you might want to do is check the sound focus and azimuth. Could also be your sound lense is shot. Also check your exciter target. And, make sure the sound lense is clean.

Tom, can you be more specific on what your "Buzz" sounds like? Is it a hum, hash noise, or does it sound like a telephone line hum?

If it sounds like a telephone line hum, you have a ground loop problem. A ground loop hum sounds like a 60HZ hum with harmonics.

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Rick Long
Jedi Master Film Handler

Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999

posted 06-12-2001 10:42 PM

"Ground-loops" are why soundmen drink.

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Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 06-12-2001 11:01 PM

...AND they are what happens when PILOTS drink!

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