Imaging and Cancellation

Discussion in 'Archived Threads 2001-2004' started by Keith_R, Oct 26, 2001.

  1. Keith_R

    Keith_R Screenwriter

    Jun 16, 2001
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    I'm still kind of a newbie to home theater. I was wondering could someone please explain to me what imaging is? also what is cancellation?
  2. Saurav

    Saurav Cinematographer

    Feb 15, 2001
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    Loosely speaking:
    Imaging is the ability of an audio system to create an "image" of the sound in front of you (for stereo) or around you (for surround sound). Taking stereo as an example, it appears like the sound paints an image, so that you can clearly "see" every individual instrument and singer separated in space, and the music doesn't sound like it's coming from the only your two speakers. You can tell that the sound of the singer's voice is coming from in front while the drummer is in the back, and the three guitarists are spread out across the width of your room (not one in each speaker and one in the middle).
    Cancellation - this is what happens when you have two speakers producing the same note but out of phase, so that they cancel each other out. Sound moves in waves, you can visualize it as a sine wave with positive and negative regions. If two speakers produce a sound such that when teh waves reach you one is in its positive half and the other is in its negative half, the net effect will be zero, or no sound. This is in theory - in practice nothing ever cancels out perfectly, so the effect you get is a big drop in volume level at the frequencies where cancellation is occuring. Improper speaker setup, especially when subwoofers are involved, is usually responsible for this.
    Hope that helps.

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