Main speakers beside TV?

Discussion in 'Archived Threads 2001-2004' started by Scott Miller, Jan 23, 2003.

  1. Scott Miller

    Scott Miller Agent

    Sep 9, 2001
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    Any rule of thumb about how far unshielded mains need to be away from a RPTV? Getting the 50 incher tomorrow and trying to get the logistics of where everything is going to fit!
  2. Paul_Fisher

    Paul_Fisher Screenwriter

    Dec 27, 2001
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    I believe 12 inches will suffice. Just as long as you don't see any discoloration on the screen you're fine.
  3. brucek

    brucek Second Unit

    Dec 29, 1998
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    There can be several problems associated with locating speakers close to the sides of an RPTV. It can ruin your soundstage and there is a potential for distortion.

    Several years ago I had a set of Studio 100's as my mains. I had them both pressed against either side of my Toshiba 50H95 for a few weeks while I was building some new shelving to house way too much audio equipment. Well, besides killing my sound stage (which I was ready for), it had a small magnetic effect on my outside CRT's. I was surprised, because I felt the outer CRT's (red and blue) were far enough away from the lower magnets in my woofers to have no effect.

    I only noticed the small problem that the magnets were causing when I watched some text scrolling up the screen. Specifically the blue, which happens to be the right hand CRT closest to the speaker. My convergence was off. I moved the speakers as a test and the convergence was fine again. Oh well, no big deal, I just tweaked the convergence and all was OK until I rearranged my stuff with my new shelves and I had to again re-converge.

    Since I had the 100's slightly forward from the front of the RPTV so that my soundstage wouldn't be completely destroyed, the magnets of the lower woofer pretty well lined up with the blue CRT inside the TV.

    My point is, a CRT, no matter whether in a direct view or RPTV, follows the same rules.
    A beam is scanned across a phosphor surface by using magnetic deflection coils around the neck. This scanned spot is a tightly controlled beam and is called the raster and if you turn the beam on and off as it scans down the screen to produce varying brightness' you end up with a picture. Simple stuff.

    The fact is though, you are able to also effect this beam with "external" magnetism. The stronger the field, the more you distort the beam. Magnetism, outside the controlled magnetism introduced by the deflection coil can cause problems. So, if the magnetic field from a speaker is in close enough proximity, it will have an effect. Large speakers with big magnets obviously have the greatest effect.

    Not that it hurts anything, but it can cause some distortion. Move the speaker away and the distortion stops.
    Keep in mind, this is a geometric distortion, and not a screen impurity that we see with direct view TV's which have a shadow mask. The result of a speaker magnet being too close to a RPTV CRT will result in convergence problems. Some speakers have shielded magnets and won't be a problem, but my Studio 100's certainly were a problem.

    Anyway, shortly after that, I got a new set of mains (ProAc response 3.8's) and moved the 100's to rear duties, with the ProAc's going into the same position beside my RPTV. The 3.8 though, has it's woofer much higher in the tower than a 100 and as a result my convergence was way off again. I reconverged and all was OK again. So it does matter what speakers you're using.....

    Anyway, it's something to watch out for if your moving speakers around your RPTV, there is a potential for distortion. As Paul says, I suspect 12 inches would be suffice for most speakers.......


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