The sound field

Discussion in 'Archived Threads 2001-2004' started by Keith_R, Jul 19, 2001.

  1. Keith_R

    Keith_R Screenwriter

    Jun 16, 2001
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    I'm still kind of a newbie to this hobby and I started wondering, everyone recommends having your rear surround speakers elevated (which is why I now have them sitting on stands) to create an accurate soundfield. I started wondering though how can that work? sure, in certain movies you can recreate the sound of a jet flying above and behind you but not all movies have a jet lifting off or flying. Take "Die Hard" for example where Bruce kills the first terrorist, remember where that terrorist shoots at the floor and the sound channels to the rear speakers on a 5.1 set-up... If your speakers are elevated how can it sound accurate? the sound will get channeled upwards instead of downwards. I'm not saying that the elevation stuff doesn't work because I'm already noticing a difference but if the rears are elevated how does it create a accurate soundfield for a thing like this? sorry about the long-winded post but I'm interested in learning more, can someone help me on this? thanks.
  2. Bob McElfresh

    Bob McElfresh Producer

    May 22, 1999
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    There is some history that might help:
    When we first started using rear-speakers, we has Dolby Pro logic that took a stereo signal and did some fun stuff with it:
    - It could strip off dialog and send it to a dedicated center/dialog speaker
    - It could strip off ambiant noises (wind, rain, humm, etc) and send the SAME signal to 2 rear speakers.
    Since the same signal went to both rear speakers, the movies could NOT have sounds go just to the left or right.
    And since these sounds were only for "ambient" or "effects" sounds, they did not want you to tell where the sound was coming from. So they wanted you to use a special speaker called a "dipole" that fired sounds along a wall. And they wanted you to mount these speakers up high to also hide their location. (They were also limited in that you could only send sounds above 120 hz to them).
    Now comes along Dolby Digital. This allows you to send sounds to any one of 5 speakers. The rear speakers were no longer limited to the same sound, or limited to "ambient" sounds.
    So Hollywood engineers started to defy the old ways and send specific sounds to one rear speaker or the other.
    Slowly, movies evolve and now start to sound better if the rear speakers are lowered so the tweeters match the height of the fronts.
    But it has taken years to get to this point. And there are still DVD's being produced with only ambient sounds to the rears. These still sound fine with a high rear-speaker placement.
    So it's basically a disk-by-disk decision: some sound better at ear-level, others sound better with a high placement.
    (Note: This is my observation/opinion and is not accepted by everyone. Seek other advice.) [​IMG]
    My rears: at a level to match the tweeters on the front.
  3. Kevin C Brown

    Kevin C Brown Producer

    Aug 3, 2000
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    My own personal take.
    I used to have dipoles up high in the back. I really liked the sound. But one quick impression I had watching Saving Private Ryan: "Wow, it sounds just like the bullets are going over my head!"
    I then went to direct radiators (bipolar actually) at ground level. (Moved what I had for mains to the rear, and got 2 more bipolars for the fronts.)
    Now, I am "in" the soundfield, rather than "under" it.
    And actually, with the bipolars in the back, they draw a lot less attention to themselves than the dipoles up high did. That's a good thing!

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