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Would an audio test CD help trouble shoot a rattling noise in speaker?

Discussion in 'Electronic Repair' started by eastcoastguyz, May 3, 2007.

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  1. (Please be kind, I am not an audio expert.)

    I have a TV which makes a rattling noised when certain low frequencies
    are played at a normal volume. This happens from either cable or
    playing something from a DVD. Before I remove the cover and start to
    try tightening screws up and other things, I would like to be able to
    duplicate the problem while attemping to fix this problem.

    I thought perhaps this could be done with an audio test CD I have
    heard about. I was thinking I would play it through the DVD player
    connected to the TV, and then when it makes the rattled, know that I
    have isolated it to begin to fix this.

    I don't know if I would have any other use for a $100 audio test CD
    beyond this purpose, so I was wondering if there already exists some
    audio test samples that are free I could download someplace that would
    do the trick. The rattle doesn't happen often enough to simply leave
    the TV on while trying to duplicate the problem. I don't know how low
    of a frequency it is, just that it is low when it rattles. This is
    just a normal JVC TV, no surround sound or anything additional added
    to it. Thanks!
     
  2. Mr.T

    Mr.T Guest

    Fairly common for the small cheap speakers used in most TV's to rattle when
    any significant bass levels are attempted.
    Why not just use one of the DVD's you are already having trouble with?
    Turn up the volume, and bass controls if your TV has them. Plug the
    subwoofer output from the DVD player into the TV audio inputs if you can,
    then play almost any action movie with lots of low frequency rumble.
    Can you plug your computer sound output into the TV audio input? Then you
    need a sinal generator/oscillator program that you can adjust the frequency
    to find the worst resonance frequencies for the TV speaker. But yes you
    could also make your own test CD's for nothing using a program like
    Audacity. A low frequency sweep signal is usually helpful.

    Frankly I find simply tightening the speakers and packing any plastic
    surrounds with rubber to stop vibration helps, unless you want to really fix
    the problem by using much better external speakers. That always works for
    me.

    MrT.
     
  3. No point - wouldn't help. The usual way is to feed 3 VAC into the audio
    system and look for the rattle. Failing that, you need an audio generator to
    drive the system.
     
  4. **No need to shell out big Bucks on a test CD. Just burn your own. Here is a
    freeware package which should allow you to do just that:

    http://www.dr-jordan-design.de/signalgen.htm

    Just dial up a low frequency (say 50Hz) and test.
     
  5. http://www.lindos.co.uk/cgi-bin/FlexiData.cgi?SOURCE=SeqsAndSegs

    Seg 8 - the slow sweep - is ideal for this purpose.
     
  6. N Cook

    N Cook Guest

    Its surprising how much distortion can be due to just a paper clip or bit of
    machining swarf touching the cone and attracted by the magnet. Try a
    different speaker on the same feed is my suggestion.
     
  7. Don't remember what web site but I was able to download a couple drum
    samples which greatly aided my troubleshooting once. The piece I was working
    on didn't even act up using sine waves, only when lower frequency music was
    being played.

    Maybe Google "download drum sample" and see what you find.


    Mark Z.
     
  8. The best check is a warbling sweep. Check out the one I suggested earlier.
    That's what speaker makers use.
     
  9. GregS

    GregS Guest

    Sine waves can detect resonances. I have always used low bandwidth music,(AM radio)
    to shake up rattles in the higher registers. All you have to do is turn the switch
    and work the knobs, or buttons.

    greg
     
  10. Trouble is you can't *guarantee* random music will have the correct
    frequencies to show up a rattle etc. Hence the idea of using a repeatable
    test. The beauty of the 'warble' is going either side of the spot
    frequency tends to excite any resonance more readily.
     
  11. Mr. Land

    Mr. Land Guest

    How old is the TV?

    I've seen really old ones where the cement used to adhere the speakers
    voice coil wire to the paper cylinder has deteriorated with age such
    that some of the windings come loose now float around, scraping
    against the other parts of the speaker. This is especially audible at
    lower freqs. I'd bet that's what it is.
     
  12. mark

    mark Guest

    Why not just try another speaker if it's old a lot of times the cone is
    torn or the speaker is just bad in some way.
     
  13. If the TV has an optional audio input, I'd suggest just plugging in an
    audio cable, turning up the volume, and put your thumb on the center
    prong of the audio cable. This should generate a loud hum that is
    likely to reveal the source of the rattle. (If you don't have a cable,
    stick a small screwdriver in the audio input and touch it with your
    finger while jiggling it around a bit.)
     
  14. Jeroni Paul

    Jeroni Paul Guest

    I had a similar problem, it had that flex thing that surrounds the
    speaker cone broken. It was of some aged material that fell off just
    blowing air at it. Fixed it with fine paper adhesive.
     
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