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.

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"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, 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.

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.

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:

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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
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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

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.