Frequency on sub test tone

Discussion in 'Archived Threads 2001-2004' started by Sebastian, Jul 18, 2002.

  1. Sebastian

    Sebastian Second Unit

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    I was wondering when you are running a test tone from VE or test tones from a receiver. What frequency is being outputted from the sub?
    Thanks
     
  2. jeff lam

    jeff lam Screenwriter

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    I believe its a range of frequencies which is why the needle on the SPL meter fluctuates a little. If you actually watch the driver during the test you will see that it isn't a constant movement, it moves in and out in all different ways.
     
  3. Sebastian

    Sebastian Second Unit

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    So are you saying that during the test tones it would start at your crossover freq and go down to 20 or 30 Hz and then back up?
     
  4. Eric T

    Eric T Second Unit

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    I think it's like the white noise that's used for your other speakers -- lots of frequencies all at the same time. Except in the case of the subwoofer test tone, it's a smaller and lower frequency range.
     
  5. Phil Iturralde

    Phil Iturralde Screenwriter

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    Actually, the LFE Test Signal in Video essentials is Band-Limited Pink Noise. (Title 7: Subwoofer Channel) The other channels = Pink Noise.
    Band-Limited Pink Noise - Dolby specifies that the subwoofer response should not go above 120 Hz, so the test noise used for subwoofer calibration should be band-limited pink noise, low-pass filtered at 120 Hz.
    band-limited: A signal is said to be band-limited if its frequency content is restricted to a particular frequency range. For instance, the output signal of a CD player is band-limited to 20kHz by the reconstruction filters built into the player.
    pink noise: A type of random noise which has a constant amount of energy in each octave band, as opposed to white noise, which has equal energy at all frequencies. Pink noise can be made from white noise by passing it through a filter with a 3dB per octave rolloff. Pink noise is used to align the frequency response of tape recorders and loudspeaker systems.
    Video Essentials playback SPL @ -30dBFS = 75 dB SPL playback
    The reason your Radio Shack SPL Analog Needle varies during this test, is due to long lower frequency wave length (ex. 32-feet for 32 Hz), plus your sub & room boundaries interaction. Some HT rooms are better than others.
    I get a 5 dB swing, so when I say that I REF Calbrate my SVS 25-31PCi = 77 dB, the lowest swing is 75 dB and the highest swing = 79 dB.
    Phil
     
  6. Johnny Mac

    Johnny Mac Stunt Coordinator

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    79? Live a little man! I'm swingin up around 82. [​IMG] Kidding Phil. Thanks for the info.
    BTW, i'm on a slab and not corner loaded so i'd bet my 82 sounds about the same as your 79. Just a guess though.
     
  7. ling_w

    ling_w Second Unit

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    Why can't they make make a pink noise that is of true equal energy where the SPL (or actually voltage) is truely constant at any given time, instead of this random hiss which has to be compensated for by the slow setting of an SPL meter.
     
  8. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    >>>I was wondering when you are running a test tone from VE or test tones from a receiver. What frequency is being outputted from the sub?
     
  9. Kevin C Brown

    Kevin C Brown Producer

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    You can also use a discrete test tone CD like Stryke or Autosounds 2000. Best way to test *across* the crossover frequency to the sub anyway.
     
  10. BruceD

    BruceD Screenwriter

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    I think using a 1/3 or 1/6 octave warble test tone scale is the best way to calibrate the crossover.

    The warble test tones don't interact with the room to produce room modes in the bass frequencies like single frequency test tones do. Interaction of "boomy" room modes makes optimization of the bass xover almost impossible.
     
  11. Kevin C Brown

    Kevin C Brown Producer

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    Ahhh, but I use a parametric eq to take care of the peaks. I mainly use plotting discrete tones through the crossover as a method for getting proper phase between the sub and mains...

    Plus, using the plot, I can get a much better match in levels between the sub and the mains. Like a lot of others, the meter reading jumps around too much with the generic sub tones from my processor and Avia or VE. Not so with discrete tones.
     
  12. BruceD

    BruceD Screenwriter

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    Kevin,

    I too use a parametric EQ, and to be clear, the warble tones are actually discrete 1/3 octave tones.

    Warble tones have a center frequency that is slightly varied to prevent room-mode buildup from showing up on the SPL meter. This allows you to do a more accurate job of blending a sub-to-mains xover setup.

    The Stereophile test cds #2 and #3 have 1/3 octave warble tones on them. Other test CDs do as well, but I'm not sure which ones.
     
  13. Wayne A. Pflughaupt

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