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Topic: Torus Screens

Dave Cutler
Master Film Handler

Posts: 277
From: Centennial, CO
Registered: Jun 2000

posted 07-24-2000 06:22 PM

What is everyones opinion on Torus screens?

Before I ever saw one I thought they were a great idea. Then I started at a theatre that has 8 of 24 Torus screens. I hate them now. Why? Speaker placement. You got your mids and highs all up top along the ceiling, and the subs along the floor. It sounds like crap, especially in a stadium auditorium if you sit on the ground level. Also the image is really distorted if the screen isn't shaped perfectly (they sag at the bottom curve) and if you have drop down masking, FORGET IT! The speakers (highs and mids) are then detached from the image, not to mention the torus becomes inconsistant from top to bottom. UGH! <GRRRRRR>

While I am at it, does anyone like single curve solid screens. I don't like those either for the speaker reason from above.

I much prefer a single curve perforated screen over any other. That way the screen channels can all be BEHIND the screen where they should be.

So what's your opinion?

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Nic Margherio
Film Handler

Posts: 91
From: St. Louis MO, USA
Registered: Dec 1999

posted 07-24-2000 07:00 PM

Yes Torus screens are lousy, all those undesirable things you brought up about them are accurate. And, if I may add a thing or two, they cause a very close-following echo especially noticeable around dialog (or at least all the Torus auditoriums I've heard have this problem.) and a "whisper wall" effect that enables one to hear a conversation taking place, say, 12 rows away and 8 seats down. Its really quite eerie. I'm sure these two phenomena are in some way related to the eliptical (and non-perforated) nature of the screen and thus, to each other. Not to mention they cost about twice as much as a regular screen of comparable size, which is why AMC FINALLY stopped installing them.

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Brad Miller
Administrator

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

posted 07-24-2000 07:31 PM

We've had a similar discussion on this in the past. I say flat screens. I've never seen a curved screen that I like. Many will disagree, but I don't like them.

You might want to do a search for "curved" and see what everyone had to say about it a while back.

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Dave Cutler
Master Film Handler

Posts: 277
From: Centennial, CO
Registered: Jun 2000

posted 07-24-2000 08:24 PM

I had forgotten that you had gotten the search back up, thanx Brad.

Nic, when did AMC stop with the torrus? BarryWoods was built in opened in late 1997 and has 8. I am glad to hear that they made the right decision for future theatres.

Flat screens are also very nice didn't mean to omit that from above. It slipped my mind, I haven't seen a film on a flat screen in a while.

Any perforated screen is better than a solid one.

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John Pytlak
Film God

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

posted 07-25-2000 07:11 AM

If you have enough light to use a low gain (gain = 1) matte surface, a flat screen installation is the way to go. Gain screens need to be properly curved to maintain good uniformity throughout the auditorium. SMPTE Recommended Practice RP 95 "Installation of Gain Screens" recommends a curvature having a radius of 1/2 X (Projection distance + Distance between screen and audience center), and a tilt of 1/2 X (Projection angle to screen center).

A gain (specular) screen is somewhat like a mirror, where the angle of incidence equals the angle of reflection. So ray-tracing is often used to optimize the curvature and tilt for a particular auditorium.

The theory behind the "Torus" screen design was published in the Fall 1997 issue of Kodak's "Film Notes for Reel People" in an article by Glenn Berggren and Gerald Nash of Sigma Design Group:
http://www.kodak.com/US/en/motion/newsletters/reel/fall97/screen.shtml

Since a perforated screen cannot be used for the current "Torus" design, speakers cannot be placed behind the screen, which is an issue. The "whisper wall" effect and geometric distortion issues have also been noted. The design does deliver high light efficiency and good illumination uniformity.

------------------
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 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

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Gordon McLeod
Film God

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

posted 07-25-2000 08:41 AM

Actually the later AMC put the bass up top as well
The echo is due to the lack of absorbancy in the side walls
Some expert at AMC decided that with slightly splayed walls there would be no need for expensive wall treatment
Check out the pics of AMC Kanata as the wall angles are visible
Also the same expert was the probably the one who decided on the amount of room isolation

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John Pytlak
Film God

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

posted 07-25-2000 09:18 AM

Gordon:

Interesting photos of the AMC Kanata. Just as a curved screen can help focus the light back to the audience, it unfortunately can also focus sound reflections back too.

I looked at a few of the other AMC theatres in the Film-Tech Projection Picture Warehouse. Looking at the last photo of the AMC Studio 30 in Mesquite TX, I hope they have cleaned out some of the dirt in the air ducts through which they run film during interlocked operation!

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 07-25-2000 09:44 AM

Hey Gord,
You mean to tell me that they actually have experts at AMC? Thats a new twist!!
Mark

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Nic Margherio
Film Handler

Posts: 91
From: St. Louis MO, USA
Registered: Dec 1999

posted 07-25-2000 02:08 PM

Mark, rest assured that there are not any experts at AMC. Dave, they decided to stop buying Torus screens in December of '98 though they were already in the plans for several theatres at that point. My theatre thankfully has none, the four "big houses" (2 - 289's, 2 - 207's) have slightly curved perforated screens, 2 side moving, 2 top moving. It was opened in September of last year. Its now the small theatres that are the problem - all of them have non-perforated sigle-axis curved screens! All the portions of the channels, lows, mids, and highs, are hanging from the ceiling! To make it worse, they are all top-moving maskings. I cannot understand it one bit, but it does go to show that there're certainly are no experts at AMC.

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Dave Cutler
Master Film Handler

Posts: 277
From: Centennial, CO
Registered: Jun 2000

posted 07-25-2000 02:29 PM

While there are no experts at AMC Corporate, I can think of two at the theatre level atleast that seem to care about quality. Namely Nic and myself!!

Any other AMC booth ushers/managers hanging around here? I would say projectionists but that's taboo at AMC, although I go clock in under Projectionist.

Nic, I find it funny that they hung the screen channel subs from the ceiling too. Is there even enough room up there? There must be a lot of masking between the ceiling and the top of the screen. Did the mount the subs next to the highs & mids? Are the subs for the LFE channel on the floor?

How can you hang a sub anyway? Wouldn't that kill the impact of subs?

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Joe Redifer
You need a beating today

Posts: 12859
From: Denver, Colorado
Registered: May 99

posted 07-25-2000 03:45 PM

Torus screens suck! And they do, literally! Not even the people who designed Torus screens can deny the fact that they suck, because it actually is a fact!

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Nic Margherio
Film Handler

Posts: 91
From: St. Louis MO, USA
Registered: Dec 1999

posted 07-25-2000 09:59 PM

The drivers are oriented horizontally rather than vertically in order to fit them between the ceiling and the screen. The LFE woofers are on the floor. As bad as this setup is for room acoustics, the main problem we have with sound quality is the EQ's - they are horrible! I probably could have done a better job with my ears. Which brings up question I have - where does one learn how to EQ? Do you learn from an experienced tech, a master/apprentice kind of thing? Is there a course you take? Is there any kind of certification?

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John Walsh
Film God

Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999

posted 07-26-2000 08:57 AM

Usually, you just watch someone do it. It's not hard to get the EQ to be acceptable or even good. But it does take some practise to get it to sound great.

While I'm sure there are classes that you could pay for, I think you sould be able to find someone to show you for free. When I was doing it, I would gladly show anyone if they just helped me carry all the stuff to/from the car.

The only certifications are from Dolby and THX/TAP. But, it's not absolutely necessary. I know several techs who are excellent at EQ'ing and are not certified at all.

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Dave Cutler
Master Film Handler

Posts: 277
From: Centennial, CO
Registered: Jun 2000

posted 07-26-2000 10:47 AM

Nic, you have problems with EQ's too? For the most part mine are terrible as well. I have one SDDS house that sounds good and it was EQ'd by an independant Tech not too long ago. Both my SRD and both of the DTS houses sound good, but the SDDS in those houses suck.

Has anyone noticed that you can't get a real black on a Torus screen. They just reflect too much light. Same goes for any solid, but not as bad as a Torus.

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Scott Morrison
Film Handler

Posts: 9
From: Los Angeles, CA, USA
Registered: Sep 1999

posted 07-27-2000 02:16 PM

Ahh, Torus Screens.
I just did a press screening of 'Space Cowboys' at AMC Gulf Pointe 30 in Houston, TX and I found a new reason to dislike them, aside from those already mentioned. During the shuttle launch sequence in the film, the subwoofers set up a standing wave ripple on the sheet itself. So you have a visible ripple on the screen which kind of looks like a video distortion, a ground loop through a video monitor or some such. Interesting from a physics point of view, but annoying during a presentation. Don't know if the phenomenon is specific to that size screen (it was a 600 seat house) and speakers, the frequencies used in the mix of the film or what.
As far As AMC eqs, most AMC theaters I've been in have the amplifier gains (balance between highs, mids and lows) set drastically wrong, so then whoever tries to eq with the third octaves on the ultra*stereo and SDDS units dials in way too much boost and cut to try to flatten it out. I would gladly set things right, but since I can't re-EQ the SDDS, I have to leave it alone (or worse yet, put it back the way it was) or it will sound awful when playing in digital.
All other interesting effects I deal with regularly, as they are relatively well known, except to filmakers who are constantly amazed at the construction and technical details of an AMC stadium house.
My favorite is the 6db level drop from the center (sweet spot) rows to the back of the auditorium, this is roughly 2 fader notches on a standard Dolby fader, so if its playing at '7' in the center of the house, its only at '5' in the last row.

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