Film-Tech Forum ARCHIVE: 9K or 7k sound test film question

This is topic 9K or 7k sound test film question 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=002281

Posted by Bernie Anderson Jr (Member # 410) on 05-17-2001, 08:12 AM:

I was trying to adjust the alignment on my 9050 rca. I have a 7k test film and ran it and all I heard was a slight quiet squeal even at almost full volume. Now, from what I remember the last time I usd this film on my friend's machine, the squeal almost knocked me out of the booth. So what's wrong here? Any ideas?

Bernie

Posted by Josh Jones (Member # 447) on 05-17-2001, 10:35 AM:

Sounds like your sound lens is out of focus. On a 9050 like mine, unlock the focus ring on the sound objectives. twist the lens ring back and forth until you get maximum level. but before you go to all that trouble, make sure the cell has a good connection. otherwise you will be screwing with the focus when you dont need to.

Josh

Posted by Paul G. Thompson (Member # 655) on 05-17-2001, 02:35 PM:

In addition to the sound lense being out of focus, the lense could be oil-fouled.

How does the 1Khz track sound?

Also, make sure the solar cell is clean, and the sound lense is clean (on both ends) and make sure the exciter lamp is "targeted" correctly. Also make sure you have the correct exciter voltage. Too low of a voltage on the exciter will prevent proper illumination on the sound track, and at or close to 100% modulation, distortion will occur.

Remember, when you run the test tracks, make sure the emulsion side of the film is to the REAR! If you don't do this, you will have a hf roll-off of a few db's.

A word of caution: If the azimuth adjustment stops were defeated, I would not recommend any attempt to make a sound focus run unless you have buzz track, a pink noise loop, and cross-talk if you have a stereo application. To use pink noise and crosstalk loops correctly, you will need a dual trace oscilloscope. If you are mono only, an oscilloscope is not necessary, but a Real-Time Analyzer is! Make your sound focus and azmiuth adjustments at the same time with a pink noise loop, and you will have much better success.

If the sound lense is up to snuff, and the output is reasonably flat as measured at the output of a known good preamp that has the correct impedance match and configuration, and the HF appears to be very low in the auditorium, I would suspect you have a blown or dis-connected HF driver, a goofy cross-over, or an amplifier problem.

Make sure you have the right exciter lamp. I have seen some vertical filament lamps used in RCA and Simplex applications out of hindsight by the projectionist and suppliers.

Posted by Gordon McLeod (Member # 33) on 05-18-2001, 11:15 AM:

The width of the slit is the cicker on most old RCA's many of them had a 1.5mil slit and as such they had a built in academy curve in the optics

Posted by Bernie Anderson Jr (Member # 410) on 05-18-2001, 01:11 PM:

academy curve in the optics? What does that mean? I took out the slit lens to have a closer look at what's going on. Well, when you hold it up to the light looking through the front you can see that it's real hazy on the inside as if oil got in there years ago and never left. When you look throught the back you see the slit but it looks like it's blocked in spots across the slit. In other words the slit isn't complete across. Could this account for the lack of high end frequency? Okay, let's say that the lens has gone bad. With improved newer technology over the past years is there a different slit lens that I should get? I'm assuming that if this one is bad the other machine is too. They're matched from the same drive in. some info:
It's a 9050 soundhead with a kelmar mono solar cell. The amp is a kelmar AS8800. Thanks

Bernie

Posted by John Pytlak (Member # 331) on 05-18-2001, 01:50 PM:

A web search found this site:
http://kvayclub.chat.ru/ranelib/par-book.htm

"Academy curve The name of the standard mono optical track that has been around since the beginning of sound for film. Standardized in
1938, it has improved (very) slightly over the years. Also known as the N (normal) curve the response is flat 100 Hz-1.6 kHz, and is down 7 dB at
40 Hz, 10 dB at 5 kHz and 18 dB at 8 kHz. This drastic "dumping" of the high-end was to hide the high-frequency "frying" and "crackling" noise
inherent in early film sound production."

"X curve (extended curve) In the film sound industry an X curve is also known as the wide-range curve and conforms to ISO Bulletin 2969, which specifies for
pink noise, at the listening position in a dubbing situation or two-thirds of the way back in a theater, to be flat to 2 kHz, rolling off 3 dB/oct after that. The
small-room X curve is designed to be used in rooms with less than 150 cubic meters, or 5,300 cubic feet. This standard specifies flat response to 2 kHz, and then
rolling off at a 1.5 dB/oct rate. Some people use a modified small-room curce, starting the roll-off at 4 kHz, with a 3 dB/oct rate."

Here are some other links regarding "Academy Curve" rolloff in optical sound frequency response:
http://www.bandradio.com/glossary/?wordname=Academy%20curve
http://www.northbeachpost.com/acad.htm
http://www.dmxl.net/coursenotes/audioforvideo/afv14.html
http://www.mtsu.edu/~smpte/seventies.html
http://www.filmjournal.com/displayfeatures.cfm?UI=9803&ID=38
http://www.robertmargouleff.com/publications/surround_0100b.htm

------------------
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 Paul G. Thompson (Member # 655) on 05-18-2001, 02:35 PM:

Bernie, from what you described, your sound lense is shot, and should be replaced.

John, with the information you provide on these forums, I am going to start printing all that stuff out and start making training folders from it. I have learned more from your posts than you can imagine. Thanks for the wealth of information.

Posted by John Pytlak (Member # 331) on 05-18-2001, 03:47 PM:

Paul:

Thanks. I enjoy helping. I certainly don't know everything, but I usually know where to find the information. Kodak knows that "Film Done Right" is more than just making better film.

Posted by John Walsh (Member # 168) on 05-19-2001, 12:28 AM:

Bernie: I think what Gordon meant by "academy curve in the optics" is that, because of the slit width, the volume drops dramatically as the frequency goes up.

It does sound like the sound lenses should be replaced. For a mono system, it shouldn't be too expensive.

An internet search for sound lenses came up with:

THE MARBLE COMPANY INC.
P.3102 Ambrose Avenue
Nashville, TN 37207
(615) 227-7772
FAX: (615) 227-7008
Email: randy@drive-in.net
President: Brad Blevins
Sales Manager: Randy Bauch
In business: 36 years, ITEA
Sankor lenses, Datamax thermal ticket printers, splicing tape, booth supplies, double eagle carbons, reflectors Osram bulbs, sound lenses, laser lens, splicers, exciter lamps.

CINEMA PRODUCTS INTERNATIONAL
1015 5th Avenue N.
Nashville, TN 37219
(800) 891-1031/(615) 248-0771
FAX: (888) 891-0554/(615) 248-2725
E-mail address: dave@cinprod.com
Website: www.cinprod.com
President: Ron Purtee
Controller: Elizabeth E. Langley
Domestic Sales: David Bevilacqua
In Business: 4 Years, ITEA
Complete line of booth supplies, including Sankor Lens, splicers, Xenon lamps, Projection ports, crowd control, Projection/Sound Equipment, splicing tape and many more items. (Strong, Peavey, Phonic Ear, FPL, Hi-Tech, Kelmar, NT Audio, Smart Devices, TECO, many more)
Branch office: Nashville

50100 Cinema Products International T-1 Sound Lens .59 Slit Width, For Use With Simplex/Century $227.27

50110 Cinema Products International T-12 Sound Lens .47 Slit Width, For Use With X- Narrow Si... $312.50

50120 Cinema Products International C-1 Sound Lens .59 Slit Width, For Use With RCA $306.81

50130 Cinema Products International C-12 Sound Lens .47 Slit Width, For Use With X-Narrow RCA $335.22

50140 Cinema Products International F* Sound Lens .63 Slit Width, For Use With RCA 90-30, B ... CALL

50150 Cinema Products International X-11 Sound Lens .43 Slit Width, For Use With Cinemeccanica... $392.04

Stereo Solar Cells
53100 Simplex $150.00
53110 Century $150.00
53120 RCA $170.00
53130 Cinemeccanica $369.00
53140 Ballantyne $170.00

Posted by Paul G. Thompson (Member # 655) on 05-19-2001, 01:54 AM:

Bernie, check the CP-55 installation manual (part 2) page 77 on Film-Tech manuals.

It shows what you can expect for a hf roll-off for a given slit lense. The 1.5 mil slit lense starts its roll-off at slightly less than 2khz, and continues to roll off to a -10db level at 9khz. This simply means that if you measured a certain voltage at the output of the solar cell (let's just pick a value of 100mv at 1Khz), you will measure 31.62 mv at 9khz. This represents a -10db drop in output.

A 1 mil slit lense starts its roll-off at about 2.5khz and continues the roll-off to a -8db at 12.5khz. 100mv at 1khz will yield 39.81mv output at 12.5khz.

It should be noted that I used calculations dealing with voltages, and not current.

I stand partially corrected when I indicated a "flat response" of the solar cell output on my previous post. It is not flat in the application we are dealing with for the following reason:

The "combined" effect of lower amounts of light at higher frequencies, caused by phase cancellation due to slit width, accounts for the lower voltage and "roll off". This is what John Walsh was basically saying in his post above.

When the slit width is equal to the spacing of 1 cycle, the loss is 100%.

Therefore, the narrower the slit width is, the better the frequency response will be.

The flat response is what you will see at the output of the processor's pre-amp after the hf slit loss compensation adjustment has been made.