THX Ultra II Surround Specs... Weird?

Discussion in 'Archived Threads 2001-2004' started by Mark Zimmer, Oct 30, 2001.

  1. Mark Zimmer

    Mark Zimmer Producer

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    I was reading in the new Widescreen Review about the forthcoming THX Ultra II specs, which require the surround speakers to be adjacent to each other. That sounds pretty strange, and contrary to what little I know about imaging theory. Anyone have any thoughts on this?
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  2. Dan Hitchman

    Dan Hitchman Cinematographer

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    THX specs. seem to be getting more and more arbitrary as they go along.
    It's just licensing $$$ to them now.
    Dan
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  3. Kevin C Brown

    Kevin C Brown Producer

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    I think that's the *back* surrounds that they say should be side-by-side. And then there's still the *side* surrounds that will be on either side of the seating area. Ideally.
    I think the reason why they want the back surrounds together, is maybe destructive interference if they are set apart, because they are being sent the same mono signal.
    (Same reason why 2 subs are usually best sounding if they are stacked, rather than separated in a room.)
    Maybe? [​IMG]
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  4. Larry Chanin

    Larry Chanin Stunt Coordinator

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    Kevin:
    Dolby Surround EX that has a mono surround back channel.
    THX Surround EX is the Dolby Surround EX process licensed by Lucasfilm for use in homes. It also has a mono surround back channel.
    THX Advanced EX (Ultra2 processing) derives two different back surround channels from non-Surround EX 5.1 encoded material.
    From what I have read, the human ear sometimes has difficulty discriminating sounds coming directly from the rear on the listener. When this happens there is a psychoacoustic effect in which sounds coming directly from the rear are perceived as coming directly in front. These rear – front reversals are said to be greatly reduced by placing two back surround speakers about 150 degrees from the front. (I liken it to an audio form of parallax.) This is supposed to apply to both single and dual channel back surrounds. That is, it is recommended that even though Dolby Surround EX is only mono, a second adjacent back channel speaker is recommended to reduce these reversals.
    Larry
    [Edited last by Larry Chanin on October 30, 2001 at 04:28 PM]
    [Edited last by Larry Chanin on November 01, 2001 at 09:41 AM]
     
  5. Kevin C Brown

    Kevin C Brown Producer

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    I'd buy that for a dollar! Thanks for the explanation.
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  6. Mark Zimmer

    Mark Zimmer Producer

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    Larry,
    Don't you have those same psychoacoustic effects if you stick both of those rear surrounds together and put them directly behind? The 150-degree angle part makes sense, but this spec seems to completely undo that.
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  7. Cortney J Beard

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    THX places the back surrounds next to each other because most people are simply sitting to close to them and their rooms are just to small to trick your mind enough. If your room where sixty feet long and twenty-five feet wide you can spread them out much more.
    Cort
    ps sure THX is about the $$$ but they must be doing something right to be making all the money.
     
  8. Lewis Besze

    Lewis Besze Producer

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    [​IMG]
    Good one!
    THX is simply tring to reinvent the wheel here again.
    First they co develop the "format" with Dolby,then the home version must have 2 speaker outputs in order to receive the THX EX certification,now with THX II they put those speakers side by side,so it could receive ,yet again another certification.
    It will only gonna get worst,before it gets any better. [​IMG]
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    [Edited last by Lewis Besze on November 01, 2001 at 01:47 AM]
     
  9. Larry Chanin

    Larry Chanin Stunt Coordinator

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    Its been my understanding that 7.1 channel playback with two back surround speakers has been around a long time as part of Lexicon’s Logic 7 process, long before Home THX. (Meridan may also have been an early adopter of 7.1 processing.) I would think that the Lexicon owners who have been enjoying Logic 7 since the ‘80s would definitely say that Lucasfilms (Home THX) is a “Johnny-come-lately and they have yet to duplicate what Lexicon has been doing for years. From following the reactions of Lexicon owners in various home theater forums, I would have to conclude that they do not consider Lexicon’s implementation of two back surrounds to be just a money-making gimmick.
    Maybe seeing the increasing popularity of 7.1 channel system, Luscafilms is trying to capitalize on that market with this latest surround mode. Some speculate that this will also induce Dolby Labs to release a 7.1 version of Dolby Pro Logic.
    Larry
     
  10. Jay Mitchosky

    Jay Mitchosky Producer

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  11. Larry Chanin

    Larry Chanin Stunt Coordinator

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    Jay:
    Thanks for the correction. [​IMG]
    After doing some additional reading I realize that I was also confused between Dolby Digital Surround EX and THX Surround EX. In my original posting I listed them as:
    What I should have said was:
    Dolby Surround EX that has a mono surround back channel.
    THX Surround EX is the Dolby Surround EX process licensed by Lucasfilm for use in homes. It also has a mono surround back channel.
    THX Advanced EX (Ultra2 processing) derives two different back surround channels from non-Surround EX 5.1 encoded material.
    To avoid confusing others who may read this thread, I've gone back and corrected my original posting.
    Sorry for my confusion. Now that I'm back on the same page as everyone, didn't Lucasfilms switch from recommending either a pair of dipole, or direct radiating surround back speakers under THX Surround EX, to a pair of direct radiating surround back speakers under the THX Advanced EX spec?
    This is probably a stretch, [​IMG] maybe they reason that two direct radiating speakers, operating out of phase and mounted adjacent to one an other, will act as a large dipole array for a more enveloping surround back sound field??
    Thanks again.
    Larry
    [Edited last by Larry Chanin on November 01, 2001 at 10:04 AM]
     
  12. Mark Zimmer

    Mark Zimmer Producer

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    I don't know, but the speaker mfrs. have gotta love THX. Now you need dipoles! Whoops, bought the dipoles, now replace them with this! Whoops, bought those, now replace them with that! [​IMG] Do I smell payola?
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  13. Larry Chanin

    Larry Chanin Stunt Coordinator

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  14. Kevin C Brown

    Kevin C Brown Producer

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    I wonder if THX Ultra2 will allow for the situation of only have 6, and not 7 speakers?
    (You know, adjusts all the digital processing somehow between 2 vs 1 rear center speaker.)
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  15. Lewis Besze

    Lewis Besze Producer

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    Larry,you are correct on the Meridian and Lexicon,however,it is more of a post processing by the processors themself,and not part of the movie mix[which isn't mandatory ,but that's how it was intented].
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