This is topic exciter sound problem in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=002351
Posted by Patrick de Groot (Member # 858) on 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
Posted by John Pytlak (Member # 331) on 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
Posted by Gordon McLeod (Member # 33) on 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?
Posted by Kyle Abel (Member # 819) on 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
Posted by Demetris Thoupis (Member # 833) on 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
Posted by Darryl Spicer (Member # 711) on 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.
Posted by Gordon McLeod (Member # 33) on 06-05-2001, 06:27 PM:
Not all excitor supplies used in european machines will accept the grounding of one side of the powersupply
Posted by Tom Kroening (Member # 201) on 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.
Posted by Patrick de Groot (Member # 858) on 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.
Posted by Brad Miller (Member # 2) on 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.
Posted by Patrick de Groot (Member # 858) on 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.
Posted by Patrick de Groot (Member # 858) on 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...
Posted by Paul G. Thompson (Member # 655) on 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.
Posted by Rick Long (Member # 213) on 06-12-2001, 10:42 PM:
"Ground-loops" are why soundmen drink.
Posted by Randy Stankey (Member # 64) on 06-12-2001, 11:01 PM:
...AND they are what happens when PILOTS drink! 
Posted by Paul G. Thompson (Member # 655) on 06-12-2001, 11:30 PM:
Yes, Rick. I ate a few not only in the Motion Picture Industry, but also in the Broadcasting Industry. They are really not that hard to deal with, and are usually are easy to eliminate.
Posted by Tom Kroening (Member # 201) on 06-13-2001, 04:43 PM:
Paul,It's definately not a ground loop problem. Its more of a buzz like those hairclippers that they use at the barber then a hum. It doesnt always come out of the auditorium, but always comes out of the SMART sound monitor. The monitors normal light is on and the backup light is flashing. Funny thing is the switch is set to the normal posotion. There seems to be the same hum coming from the exciter bulb itself, although it could just be the sound monitor that im hearing since they are in close proximity.
Posted by Gordon McLeod (Member # 33) on 06-13-2001, 05:05 PM:
I believe you probably have a smart combine excitor supply and monitor
When the bypass is flashing it indicates that the backup ps is in use
The problem is probably the bridge or the regulator module
Posted by Tom Kroening (Member # 201) on 06-13-2001, 05:12 PM:
Hmmm, interesting. We have two or three extra smart monitor/exciter supplies. Would you recommend swapping parts or the whole unit itself?
Posted by Gordon McLeod (Member # 33) on 06-14-2001, 12:43 PM:
Simpiler to swap the whole thing