Line array as center channel?

Discussion in 'Home Theater Projects' started by TimForman, Sep 9, 2003.

  1. TimForman

    TimForman Supporting Actor

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    Given that line arrays are very popular for mains how do you construct a matching center channel? The potential for horizontal off-axis problems exists due to the cylindrical rather than spherical sound field doesn't it? Can you angle out the end drivers or just add more drivers until you get the width you need or forget the whole idea and go with single point source?
     
  2. RichardHOS

    RichardHOS Second Unit

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    A vertical line array would have wide horizontal dispersion (good).

    A horizontal line array would have horizontal dispersion more or less limited to it's effective array length, unless it followed an arc shaped array (similar to Magnepan's center channels), but would still generally suffer from comb filtering artifacts (bad).

    In short, a center channel line array that was identical to your L/R line arrays would make an exceptional center channel. Fitting one above or below a screen or TV might be a bit of a problem though, with an acoustically transparent screen a good option.
     
  3. Scott Simonian

    Scott Simonian Screenwriter

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  4. Jim Griffin

    Jim Griffin Extra

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    If you use a near field line array for the left and right speaker channels, you may not even need a center channel. That is because the center image area is significantly larger with a near field array. In the near field the sound from a line array falls off at half the rate of point source speakers. Therefore, the sweet spot for the image becomes a sweet area--a much larger space is filled-in by the array. You can set your receiver/DSP processor or DVD player that decodes the surround sound to a phantom center and enjoy the sound. In fact, only if you have a very wide spacing for the left and right speakers would you need a center channel to fill-in.

    What would be awesome is to have line arrays for the rears so you have a very wide image area--nearly the entire room. Surround sound bliss!

    See my white paper for near field line array details. The rotten system here will not accept URLs from me (I used to be able to post links--go figure!) for the white paper but contact me and I'll e-mail.
     
  5. ThomasW

    ThomasW Cinematographer

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    My 25+yr history using line arrays leads me to the conclusion that they do provide adequate center fill for music. But for the dialogue channel of movie DVD's, the people sitting off axis do benefit from a dedicated center channel. Note that a standard MTM configuration center is frequently adequate to the task, depending on the size of the room and distance to the listeners

    Horizontal placement of a line array is almost always worse than using a 'phantom' center.

    If one has the ability to place a vertical line array center channel speaker the overall sound stage is probably the best available.
     
  6. TimForman

    TimForman Supporting Actor

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  7. John E Janowitz

    John E Janowitz Second Unit

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    I actually have a 6 driver line/center channel in the works. Although it will not have all the typical properties of a line array, it will have a very controlled horizontal dispersion to about 30 degrees off axis each direction. Basically a half moon type shape that could mount on the front wall or sit above or below a screen/tv. Yes, this is a horizontal line array to some extents, but takes advantage of the limited vertical dispersion of the ribbon tweeters, turned sideways, to eliminate the comb effects between tweeters. I do have measurements from this, and it works out great.

    I'm working on the front channel line arrays right now. I'll be working on this center channel in about a week and will post the results.

    I also have line array surrounds as well. :)

    John
     
  8. TimForman

    TimForman Supporting Actor

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    I agree with your design concept and am about to embarke an a similar venture. I found my current enclosure too long to fit in the space between the top of the RPTV and the ceiling so it's back to the drawing board. Which is ok, I've learned what not to do now.
     
  9. Jake K

    Jake K Stunt Coordinator

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  10. Jim Griffin

    Jim Griffin Extra

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    Jake,

    A line array that operates in the near field will have sound fall off that is one half the rate of a point source. But a line array can also operate in the far field wherein the sound falls off at the same rate as a point source. Conditions are given in my near field line array white paper on the audiodiycentral site at:

    www dot audiodiycentral dot com

    Replace the dots with periods for the usually web address and look for my paper on taht site. Sorry that this forum does let me post web addresses until I'm in jail for a few more postings.


    Jim
     
  11. Dennis XYZ

    Dennis XYZ Stunt Coordinator

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  12. Jim Griffin

    Jim Griffin Extra

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    Thanks Dennis!
     

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