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This topic comprises 3 pages: 1 2 3
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Topic: Where are the screen speakers in these older AMCs?
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Frank Angel
Film God
Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999
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posted 04-19-2006 10:54 PM
The problem with the torus is not so much the curve -- it's the way you have to get it -- all that super-suck air pressure pumps and the air-tight room nonsense behind the thing. If a torus screen could be made by some sort of self-supporting rigid material that didn't require a vacuum system to maintain the curve, then an X/Y concave curve matched specifically to the throw is the theoritical ideal for absolute focus and light distribution.
Thing is, in the real world, today's lamphouses and the broad depth-of-field of modern lenses are more than capable of giving perfect corner-to-corner focus and illumination without the need for the torus dual curves. Besides, the place you really need to use a high gain screen without hotspotting (which is what the torus gives you), would be in the really larger screen sizes; there you might profit from the torus in that you wouldn't need to go up to extreme lamp sizes. But it is just in those larger size screens where the torus becomes much more of an unwieldy behemoth, needing bigger suction pumps and a larger airtight space behind it.
I never saw a torus, but this came to mind -- wouldn't you need to keep the pumps going all the time, not just when the theatre is opened? If you turned the vacuum pumps off, wouldn't the whole screen sag in on itself? I would guess that could leave creases. Or maybe it wouldn't crease and you could turn it off at night. Then when you opened, it would be: turn on the marquee, turn on the work lights, turn on the booth power, turn on the screen and watch it suck itself into postion. Weird.
But that's just the physical oddity of the thing. Then there are the anomolies that any large curved surface in a room with a sound system will present. Curved surfaces are an acoustician's nightmare. There are enough theatre builds that suffer from the lack of a good acoustical engineer involved with the design -- most owners just use the "just-throw-velour-on-all-the-walls" school of acoustical design; the last thing anyone needs is to have people designing theatres without benefit of a good acoustical engineer AND have one wall a double concave reflective surface.
As for speaker placement, I disagree with Steve about speaker needing to be behind the screen. I think in theory that might be right -- for the perception of sound coming from the image, the ideal is to have the speaker place behind the screen. But what trumps theory is what happens in the real world and I can tell you that I work in two venues which of necessity, both have speakers on either side of the screen with a center channel directly above it. And again, in theory this may seem like it detracts from the desired perception that voices are coming from the actors' mouths, but I can tell you that is not the practical reality. In both these rooms, even sitting in the first few rows (which are, blessedly, about 25-30 feet from the screen) your brain matches localization just as much as when speakers are closer to the actual image. Even in the older mag mixes with panned dialogue following the characters, the illusion is not broken by the outrigged Left and Right channels. This is true even moreso with today's mixes where dialog is kept dead center, the dialogue is not moving to the actor's location on the screen anyway -- it stays nearly always dead center; your brain moves it to where it needs to be. On a 50ft screen, if dialogue is coming from the center channel and a character is at either end of the screen, the sound is pretty removed from the image, yet you still perceive it as coming from that character.
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Frank Angel
Film God
Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999
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posted 04-20-2006 10:34 AM
Well Steve, you've got some pretty acute hearing abilities, and I will agree with you that left and right localization would possibly suffer, IF dialogue was routinely placed near the screen extreme left and right edges of the screen, but as I said, even in 4trk mag mixes, dialogue is rarely placed exclusively in the left or right channel (and of course the given here is a 3 screen channel mix, not 70mm/5). Point is, localization is far more critical for left and right horizontal sound positioning than it is for vertical localization (otherwise we would have two additional ears, one on our forehead and the other on our chin). We evolved with very acute ability to hear what's coming from all around us (fast running predators of all sorts), but obviously there wasn't much threat from overhead.
Now I don't know if anyone has done any psycho-acoustical tests for this, but in my experience -- talking off the top of my forehead as Louis put sit -- I have never found that either lip sync or what I'll call "detachment" of an actor's voice from his image position on the screen, were problems that happened when a center channel speaker cluster is placed above the screen. If it is a 20ft high screen, then the center channel would be about fifteen feet away from dead center. I contend that in the vertical plane, that does not cause the problems for most of us that you say you can hear, especially in a large room where the audience concentration is usually around 30 ft from the screen. I am not denying that you are conscious of it, all I am saying is that most people are not even aware of the off-placement.
I am a recording engineer; I certainly am very much aware if and when both channels, left and right, are perfectly balanced or not, in the horizontal plane. But as for up or down....I mix sitting down, sometimes standing up, and I do this three feet from near-field monitors; in some studios the speakers are placed high, in another, right at the console level, but the vertical positioning is not critical -- and that's when you are close to the system. In a large PAC theatre, the audience is sitting a lot farther away than in a shoebox multiplex or in a screening room -- being good distance from the screen also minimizes the vertical displacement anomalies.
Bottom line is, we've had a parade of directors, cinematographers, post production mixing engineers, producers, etc., all watch their own films in our PAC with off-screen speakers and I never encountered even a minor mention that dialogue was detached or lip sync was off or that they were in any way unhappy with the sound -- one even voiced surprise when she went back stage for a Meet & Greet and noticed that there were no speakers back there. She had watched her own movie from start to finish and thought the speakers were behind the screen the whole time.
We had one client, the producer/director of a feature, use our theatre to show his film to prospective backers. He was ultra critical of every aspect of the presentation and even had his own people bring in their a CP200 to replace our older CP50. If anyone would have walked out and gone somewhere else if the sound wasn't absolutely perfect for him, it would have been this guy. He was very happy with everything, off-screen speakers and all.
So, I will grant that placement of left and right channel arrays off-screen would be problematic IF for some reason actors were routinly positioned to the far left or far right on the screen, but that rarely if ever happens. As for music, it doesn't care that the speakers are off-screen as long as there isn't a hole-in-the-middle created. As far as you saying that placing the center channel directly above the screen would somehow affect lip sync or ruin the illusion of dialogue coming from the actors, then your hearing is a lot better than most people.
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 04-20-2006 01:07 PM
The "echo" problems with torus screens are inherent to any solid surface that "focuses" sound, as in a "whispering gallery" design:
Whispering Gallery Chicago MSI
quote:
The Whispering Gallery is a marvel of sound wave communication. The two parabolic dishes and the unique shape of the room carry the quietest message from your lips to someone’s ear
Whispering Gallery Design
quote:
A whispering gallery is an area with a domed ceiling where two people can softly converse even though they are standing many feet (or meters) apart. The two most famous examples are found within St. Paul's Cathedral in London and Statuary Hall in the US Capitol.
There is also one located in the dining concourse in front of the entrance to the Oyster Bar in NYC's Grand Central Station. There is no sign marking the gallery or any instructions posted on how to make it work. However, by waiting a few moments, an in-the-know couple will walk up and show you the way.
If that doesn't happen, you and a partner need to stand in opposite corners below the tiled ceiling. You need to be facing very close to the corners, around 2 to 3 inches from it. Speak in a soft to normal tone and your friend should be able to hear you quite clearly, as if you were standing next to one another.
Over the years, Grand Central's Whispering Gallery has become a romantic spot for paramours wishing to quaintly exchange sweet nothings. It's also a popular scene for proposing marriage, especially around Valentine's Day, so be careful what you are getting yourself into.
If someone asks you how or why it works, try to recite some of the following explanation and use lots of the big words. A whispering gallery occurs beneath a domed ceiling constructed in the form of an ellipsoid with a parabolic dish at each focus (usually a corner). When someone faces one dish and whispers, the sound telegraphs from this focus until it reaches an opposite dish, where another person waits to receive the message.
[ 04-20-2006, 02:54 PM: Message edited by: John Pytlak ]
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Louis (I most certainly agree.)
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I have done many field checks with master plans that would have 2 - 3 pages of our drawings detailing speaker and hardware location and watch the blank stares from other subs why we could not "live" with it.
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