test disk for SPL plotting

Discussion in 'Archived Threads 2001-2004' started by gomez_a, Feb 17, 2002.

  1. gomez_a

    gomez_a Stunt Coordinator

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    Hello, I have an Autosound 102 test CD that has sine wave test signals that start at 10Hz and goes on up to 90Hz in 1Hz increments. .I want to plot my SPL for the sub 80Hz area of my system (of course, I won't plot every Hz :).

    Can someone tell me if its ok to use these sinewave test signals at reference level (0 dB on my rcvr) without damaging my sub?

    Or, can someone recommend a better frequency test signal CD thatI can use to plot my SPL readings

    I'll use AVIA to calibrate my system to 85dB (ie, 0 dB) with all my sats (including mains) set to SMALL.

    Thanks!
     
  2. Bhagi Katbamna

    Bhagi Katbamna Supporting Actor

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    I would be very careful with sine waves at reference level. Just test the sub response at 75-80 dB. You are looking only for the relative difference in response of your subwoofer at various low bass frequencies. The max SPL your subwoofer can produce at your listening position depends on many things including room response, amplifier power, size of room etc.
     
  3. Wayne A. Pflughaupt

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    Gomez,

    The Autosound disc will wok fine. You only need to take about sixteen 1/6-octave readings, which should be no problem for most subs. It only takes a few seconds to get a reading at each frequency. I’ve taken readings as high as 104dB with my Shiva-based subs (that was the one “peaky” frequency).

    However, you might proceed with caution if you have something small, like an 8-inch sub.

    There are the 1/6-octave frequencies:

    18Hz, 20Hz, 25Hz, 28Hz, 30Hz, 36Hz, 40Hz, 45Hz, 50Hz, 56Hz, 63Hz, 71Hz, 80Hz, 89Hz, 100Hz, 111Hz.

    Use all that apply to your sub’s extension and crossover frequency.

    Good Luck,

    Wayne A. Pflughaupt
     
  4. gomez_a

    gomez_a Stunt Coordinator

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    Wayne, Bhagi, thank you for response

    I have an SVS16-46PC and a Polk 650 sub , which I have yet to plot the SPL responses for . . so, here's what I'll do - pleae correct me where I'm wrong here:

    1. I'll line level run both subs off my onkyo 898 sub-out jack (I have a 'y' splitter going to both subs)

    2. use my autosound test cd #101 and turn volume up to 75db and plot the SPL reading (with the RS SPL meter correction factors added in) at the freq's wayne suggested

    3. when taking readings, my 2 subs will be on, but the sats and mains will be off

    a-question: how do I turn the sats and mains off? do i

    disconnect their spkr wires?

    b-question: is it ok to plot both subs together, or should

    I do them separately?

    I know the polk and SVS are seperate animals, but i do want to keep both subs in the system

    Then, based on my plot, I'll see if a parmetric eq is in order (that is, if I can't correct the peaks/valleys via moving the subs around)
     
  5. Kevin C Brown

    Kevin C Brown Producer

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    You have to do each sub independently alone 1st.

    Then, each sub by itself with the mains to get each individual's sub's phase correct.

    Then both subs with the mains.

    And if you can't turn off the mains (satellites) via your receiver (with a pre/pro, just turn off the amp feeding them) then disconnecting the wires will work too.

    Not easy, but this is the best way to avoid nasty phase cancellation effects which is very common with 2 subs spaced apart.

    BTW, a lot of people suggest that if you do have 2 subs, simply stack them together in 1 corner. You get ~6 dB more output, but no phase problems to worry about.
     
  6. gomez_a

    gomez_a Stunt Coordinator

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    yes, I stacked the SVS sub atop the Polk 650, looks strange, but it should work
     
  7. Kevin C Brown

    Kevin C Brown Producer

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    Cool. Then theoretically, the room induced peaks and valleys *should* affect both subs the same at each freq.
    I'd be curious if you do those measurements, if that's what you see... [​IMG]
     

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