Film-Tech Forum ARCHIVE: bass treble trouble

This is topic bass treble trouble in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Patrick de Groot (Member # 858) on 07-03-2001, 12:31 PM:

We've got some anoying sound problem. It seems like the bass is too high and the treble too low. I can partionally correct this with equalization, but the sound still sounds like crap... CD music sounds ok. What can couse this? Solar cell? Exciter lamp? (that one I checked) voltage, amps? We reconnected the wires coming from the solarcell to the miccable going to the MIC input.

Posted by John Pytlak (Member # 331) on 07-03-2001, 01:27 PM:

For analog sound, first thing to check would be the focus and alignment of the sound optics. If this happened suddenly, be sure the optics are clean (no dirt or oil buildup), or that someone didn't fool with the adjustment. Also check to be sure the exciter lamp does not have a defective filament (e.g., sagging). The fact that you are suddenly having to use much higher amplifier gain and have lost the high end makes me suspect something as simple as dirty optics. Ideally, should do a complete A-chain alignment to get everything back into specification.

------------------
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
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Posted by Randy Stankey (Member # 64) on 07-03-2001, 02:51 PM:

I second that.

It sounds to me like its in your A-Chain. If you look at it with your RTA you will probably see this huge dip in the middle of the curve. It could be caused by a number of things. Just do a complete A-Chain alignment and that ought to solve the problem.

Oh! And DO clean the optics! That should be the first thing you do even if somebody tells you they just did it two minutes ago. I've gotten to the point where the only person I trust is me... not because I think everybody else is stupid or something but because unless I did it myself I can't say with certainty that something was done right. Who knows, they could have accidentally used a dirty Q-Tip when they cleaned the lens and made it worse. Stranger things have happened!

Posted by Mike Horn (Member # 896) on 07-03-2001, 03:13 PM:

I don't think it would be in the equalization unless something was recently changed. Probably in the optics...

Posted by Gordon McLeod (Member # 33) on 07-03-2001, 03:31 PM:

Since the cd player sounds ok then the problem is probably in the A chain

Posted by Joe Redifer (Member # 3) on 07-03-2001, 04:56 PM:

Hmmmmm.... I'm going to go out on a limb here and say it is your A-Chain.

Posted by Darryl Spicer (Member # 711) on 07-03-2001, 05:47 PM:

yes it sounds like an A-chain problem. Also a slight chance it could be in the pre-amp card or the noise reduction card. I have had instances where the treble was effected by one of these two cards having a problem. Also what type of light source are you using. Is it the exciter white light lamps or a jax light red led? A normal exciter can cause problems if the filement drops out of position. The jax light can cause problems if it is not positioned straight on in line with the optics.

Posted by Rick Long (Member # 213) on 07-03-2001, 08:32 PM:

Patrick, give us a little about the history of this problem. Did you hit the screen one day and suddenly notice the lack of high frequency content, or has it gradually been building until it became quite noticeable. Is this happening with more than one print?

By the way, what soundhead and sound processor are you using?

Posted by Rick McCluney (Member # 642) on 07-03-2001, 09:07 PM:

Sounds like the A-chain to me too. Clean the optics first but keep in mind that if you are useing a projector with an oil leak it is possible for oil to get inside the slit lens. If that is the case, you would need to replace it.

Rick

Posted by Patrick de Groot (Member # 858) on 07-04-2001, 10:20 AM:

Thanks for you're answers.

The problem gradually developed. When the sound was becoming bad I tried several things to make it sound better: rewiring, new exciter lamp, (white light 6V 1.5A or so, the european standard), new transformer (which was necessary)
I'm going to "try" to do an a-chain alignment.

We've got no sound processor... The stereo signal goes into a stereo mixer and from there to the amplifiers.
In another auditorium we have an equalizer put between it and a dolby surround decoder(not the professional stuff, just equipment for "home" use). In that auditorium the sound sounds reasonably. Dialog is clear. Heavy bass. Only problem is the background noise from the preamplifier. (Noise reduction?) So we have a L & R sound channel and some "sort of" surround channel.

The projector is a good old Philips FP5 and the soundhead is also of the brand Philips. Has someone maybe worked with this soundhead? Slight chance...

Posted by Gordon McLeod (Member # 33) on 07-04-2001, 10:54 AM:

I don't know the soundhead for that machine but it is probably similar to the one on the FP7 or DP70. In that it had reverse scanning
You may want to check the condition of the slit
There is an excellent laser made in Switzerland that should retrofit into this machine and improve the high frequency response

Posted by Patrick de Groot (Member # 858) on 07-04-2001, 06:28 PM:

Well, I have finally made the sound sound ok!

After some experimenting with some knobs (I don't have any experience with aligning soundheads...) It was the focus of the soundlens. I am really beginning to wonder how this problem could expand like this... Some technician did take a look but didn't noticed it. Maybe because we are a small local cinema??? I'm glad www.film-tech.com exists

Posted by John Pytlak (Member # 331) on 07-05-2001, 08:59 AM:

Patrick said: "...It was the focus of the soundlens... I'm glad www.film-tech.com exists."

Glad we were able to help!