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TV vibration from Centre channel?

Discussion in 'Archived Threads 2001-2004' started by ChrisAG, Oct 5, 2001.

  1. ChrisAG

    ChrisAG Supporting Actor

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    When I really crank the volume the TV exhibits horizontal interference lines. Someone else complained about this, and the answer seemed to be vibration, cured by adding rubber feet to the speaker. This does not help in my case. If I lift the speaker off of the TV a few inches it still happens, but it is reduced. If I lift it over a foot, the problem is gone. The problem is also eliminated if I disconnect the centre speaker, so it is not caused by floor vibration from the mains (I do not have a sub).
    So, is the cause sound pressure, or magnetic interference?
    If it is magnetic, wouldn't there be interference even if there is no sound, since the magnets are still "magnetic" with no input from the receiver?
     
  2. Philip Hamm

    Philip Hamm Lead Actor

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    Do a search, this topic has very recently been covered. It is vibrations. Do you by any chance have a SONY TV?
    ------------------
    Philip Hamm
    AIM: PhilBiker
     
  3. ChrisAG

    ChrisAG Supporting Actor

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    Thanks, I saw the previous thread, but that problem was cured with rubber speaker feet. In my case I have the feet, plus:
    - when I lift the centre a few inches off of my JVC 32" TV, I still see the interference
    - when I disconnect the centre, the problem vanishes
    This tell me:
    - the mains are not the problem, so floor vibration is not a factor
    - the centre speaker is the culprit, but it is not vibration due to contact with the TV, since interference still happens when I lift the speaker 4 inches above the TV (but disappears when I lift it a foot)
    Is the "vibration" travelling through the air, i.e., sound pressure?
     
  4. Massimo N

    Massimo N Stunt Coordinator

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    Sound like it's magnetic interference. This would happen only if you crank the volume, because more current is travelling through the speaker's magnetic coil(s), making the magnetic field stronger.
     
  5. Kevin. W

    Kevin. W Screenwriter

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    Chris,
    What centre speaker do you have? I have a JVC 32"(Sears) and do not experience the problem with my Paradigm CC-350. How far forward on top of the TV is the speaker? Try adjusting its position. Does your speaker wire run up the back of the TV? Maybe your getting some feeback from the speaker wire.
    Kevin
    [Edited last by Kevin. W on October 07, 2001 at 10:21 AM]
     
  6. AndrewJ

    AndrewJ Auditioning

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    Chris, I have experienced this problem before. I was Chief Engineer at KEF in England, many moons ago, and had a customer complaint of a very similar description. In that case it was not vibration, as you have proven by simply lifting the speaker off the tv a few inches. It is not current through the voice coils either, since this is essentially shielded by the magnet structure. I believe it is electromagnetic interference from the current flowing in the crossover inductors, combined with less than perfect shielding in the tv. This is why the interference gets worse at high volume levels and manifests itself as horizontal line interference, not colour purity.
    In my particular case the crossover was mounted on the bottom surface of the cabinet, and so very close to the tv. The cure was to go inside the speaker and simply screw the crossover to the top of the cabinet. How about trying the experiment of turning the speaker upside down and seeing if it improves matters?, or at least looking inside the speaker and letting us know where the crossover is located?
    It would also help to know the make and model of tv and speaker
     
  7. ChrisAG

    ChrisAG Supporting Actor

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    Thanks for the input everyone.
    My TV is a 32" JVC. Speaker is Mordaunt-Short TXH 504. I also have a non-TXH Mordaunt-Short 905 centre channel to act as my single rear centre. I tried switching speakers, and the interference happens with the 905 as well, though not quite as much.
    I'll try it with the speaker upside down and see what happens.
     

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