Strange Sub Behavior at 50Hz

Discussion in 'Speakers & Subwoofers' started by James Grasso, Apr 18, 2003.

  1. James Grasso

    James Grasso Agent

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    I was just plotting the freq. response of my WM40 and at exactly 50Hz, there is a strange oscillation, no clear frequency can be heard, just sort of a wobbling, varrying frequency, and the dB meter goes crazy wobbling between 70 and 80 dB. Why is it doing this? Is it the room acoustics, could it just be the resonant frequency of the enclosure causing it, or something else? It does it in 2 different places in the room. It is polyfil stuffed also.
     
  2. Dustin B

    Dustin B Producer

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    Room mode. The wavelength of the those two frequencies is matching a multiple of one of your room dimensions and forming a standing wave. Standing waves can result in reinforcement (peak in response) or destructive interference (null in response).
     
  3. James Grasso

    James Grasso Agent

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    Thought so, just had to make sure it was that. Audio is wacky, crazy stuff. I love/hate the way sound does stuff like that. It's interesting, but a pain to deal with.
     
  4. James Grasso

    James Grasso Agent

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    BTW, Can anyone host a picture of an excel plot for me sometime in the near future so I can put it up on the board?
     
  5. Frank Carter

    Frank Carter Screenwriter

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    James,

    Email me with the picture and I'll put it up.

    Frank
     
  6. Frank Carter

    Frank Carter Screenwriter

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  7. James Grasso

    James Grasso Agent

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    FWIW, the Polyfil only was accidently done with a 100 Hz Receiver Cutoff frequency. All of the other tests were done with the same sub placement and the cutoff freq. was set to about 140 Hz. I'm assuming that the huge hump of this response was because of the terrible room acoustics. It's about a 15' by 9' room with sort of an arch that turns a section of the room into a 9'x9'x9' cube. The sub was placed in as much of a corner as possible.
     
  8. jeff_coil

    jeff_coil Stunt Coordinator

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    Hey James GO HAWKS [​IMG] I am in Cedar Rapids
     

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