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Center Channel not Magnetically Shielded?

By Vehementi
Jan 6, 2003
  1. Hi all,

    I think the center channel for my home theater system isn't magnetically shielded. It's a KLH 943PL, and on the box it says it is - but I don't think it is. I'm getting wavy lines on my screen whenever the center channel is playing - if I disable it from my receiver than the lines start to fade after a couple of seconds. The center channel is sitting right on top of my monitor. Should I move it? I think it's in the optimal position...

    Should I get something to put between the speaker and the monitor?

    And it's not my refresh rate...it's 75Hz...

    Even my KLH 911B front speakers aren't shielded - I think - because I can notice the waviness even when the center speaker is off, slightly, and they go away when I turn the receiver down/off.

    Thanks in advance.
     
  2. Vehementi

    Vehementi TechSpot Paladin Topic Starter Posts: 2,704

    [crossout]And it doesn't happen immediately - it takes about 30s from me turning the center channel on to seeing the waviness.[/crossout]

    Edit: ok I'm an ***** and it does happen immediately - I just didn't notice it.
     
  3. SNGX1275

    SNGX1275 TS Forces Special Posts: 10,714   +397

    Its maybe a build up of an electromagnetic field, because if it was strictly magnetic (and the thign wasn't shielded) you would get interference immediately, whether the speaker was on or not, any time it was in the vacinity of the monitor it would distort it.

    Commonly magnetic fields will make blue or green or red show up on the screen, not just wavy lines.
     
  4. olefarte

    olefarte TechSpot Ambassador Posts: 1,343   +6

    I agree with SNGX, if the speaker is not shielded properly it will cause the picture to distort even if it is not hooked up, if you get close to the monitor.

    This may sound stupid and it probably is, but is there a top and bottom to the speaker, maybe try turning it over, it might be just shielded on one side. I know, sounds stupid. Maybe you should consider returning it and getting the Yamaha you looked at.
     
  5. Vehementi

    Vehementi TechSpot Paladin Topic Starter Posts: 2,704

    Great, now I am getting magnetic interference. There's two dots on the right side of my screen - the top one is bigger than the bottom one, and all they do is just mess up the colors. With the TS window under them, it just looks a little darker. I don't notice them in black. And Degaussing doesn't help. If I point one of my front speakers at it, it gets worse. Alot worse. My right speaker is about two feet away from the side of the monitor, and it doesn't help at all if I take it away completely or turn it off.
     
  6. Vehementi

    Vehementi TechSpot Paladin Topic Starter Posts: 2,704

    I did what you said olé - and flipped the center channel upside down. It seems to help, either my vision is going bad or the wavy lines are better - either is highly plausible. I flipped the grill to make it look better too :D
     
  7. young&wild

    young&wild TechSpot Chancellor Posts: 993

    I say....why not use a nickel-iron alloy to warp the center channel.? They can shield magnetic fields efficiently.
     
  8. Vehementi

    Vehementi TechSpot Paladin Topic Starter Posts: 2,704

    :confused: :dead: And how would I go about doing that?
     
  9. olefarte

    olefarte TechSpot Ambassador Posts: 1,343   +6

    The bottom line is, a center channel speaker should already be shielded. You shouldn't have to spend extra money to shield it.
     
  10. SNGX1275

    SNGX1275 TS Forces Special Posts: 10,714   +397

    You monitor stays messed up after you take the speaker away? In that case thats bad, happened to my friends TV, he had a 12" car sub speaker about 3 feet from the tv and it messed it up permanently.
     
  11. Vehementi

    Vehementi TechSpot Paladin Topic Starter Posts: 2,704

    It's been awhile and I don't notice the waviness. I guess I've gotten used to it...:confused:
     
  12. acidosmosis

    acidosmosis TechSpot Chancellor Posts: 1,350

    I'm having a problem something like that. I have a subwoofer abotu a foot away from the left side of my monitor and it doesnt bother my monitor, BUT I put it in sleep mode and when I come back in and turn off sleep mode when the monitor is coming back on I see distortion in the colors in the bottom corners of the screen and the picture is slightly bent in those corners. It didn't start doin that till I put the subwooder near my monitor, but again like I said its about a foot away.
     
  13. StormBringer

    StormBringer TS Rookie Posts: 2,244

    That can usually be fixed by degausing it. Most monitors have a button for this, most TVs however do not, but TV repair technicians usually have a device to do it with. The one we use at the shop is just a huge ring of coiled copper wire wrapped in insulation and wired to a 115v cord. You just wave it around in circles over and around the TV while it is on, and widen the circle until you pull the distorted colors out and the images return to normal. The procedure is the same for a monitor if it is too bad for the button to fix.

    Note: Do not attempt to build the device I mentioned if you are not skilled in electronics.
     
  14. young&wild

    young&wild TechSpot Chancellor Posts: 993

    A foot away?I don't think its enough if your sub is pretty powerful. My 641 Altec Lansing (dual 6") subwoofer needs to be placed at least 2 feet away.
     
  15. acidosmosis

    acidosmosis TechSpot Chancellor Posts: 1,350

    Not surem but I believe the cone is about 6 inches, and its Altec Lansing. Its a pretty big subwoofer. I guess I will just move it back to the floor where it was. I just cant hear it that well in the floor :(.
     
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