Tom V - Sub calibration question

Discussion in 'Archived Threads 2001-2004' started by David Giles, Dec 1, 2001.

  1. David Giles

    David Giles Stunt Coordinator

    Mar 6, 2001
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    I just read the following in another thread:

    "In an excellent old post from TV. I read that the compensation numbers posted were only valid for 1/3 octave pink noise. I want to get a finer, more accurate resonse curve than that so I can set up the paremetric eq optimally. The Behringer has a tone generator, that has 1/60 octave steps. I'd like to just step through the whole range from about 16 Hz to 100 Hz in 1/60 steps, but I'm not sure how to compensate the readings for straight tones. Are the numbers I see in TVs post and elsewhere still good? (I'll interpolate linearly between the listed values - that should be close enough)"

    Okay, this got me worried. I spent several hours the other night using the Autosound 2000 CD to put out straight tones at 16, 20, 25, 31.5, 40, 50, 63, 80, and 100 Hz, then used the published values to correct the RS SPL meter. I used the results to help determine best placement for my CS_Ultra, and then to set the EQ to correct for a couple of peaks I found.

    Is it true that the correction values don't work for straight tones, only pink noise?

    Okay, now I'm thinking your going to make me feel stupid and say that pink noise is a mixture of frequencies? And to apply the correction values, you have to output specific frequencies. So maybe I'm okay after all?

    Learning is such a humbling process.

  2. Wayne A. Pflughaupt

    Aug 5, 1999
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    Katy, TX
    Real Name:
    Don’t break a sweat over the RS corrections. In the range where most people need to make EQ adjustments (40-80Hz) you’re only talking about a couple of decibels, usually less.
    The goal of sub EQing is smoother response. This has as much to do with your ears as it does measurement. Therefore clinically-accurate SPL readings aren’t necessary. For instance, your frequency-by-frequency readings might suggest the EQ needs a 1/3-octave filter centered on 50Hz and cut 10dB. However, after listening you might decide it sounds better with a 8dB cut and the filter a little broader than 1/3-octave.
    The readings will tell you what you really need to know: where the problem is and how bad it is. From that point you should trust your ears, not the data exclusively. What you might want do is plug in the corrections after you’ve made adjustments. At that point the only thing important is the filter’s center frequency. For instance, if your filter is centered at 45Hz, split the difference between the known corrections at 50Hz (1.5dB) and 40Hz (2.5dB). As you can see, you will only be making an adjustment of 1.5-2dB.
    Maybe now you can understand why I don’t waste my time with the corrections. [​IMG]
    The 1/3-octave test tones on the Autosound disc, pink noise or otherwise, are fine if you have a 1/3 octave equalizer. However, if you have a parametric EQ you might want to get test tones with at least 1/6 octave resolution.
    By the way, David, don’t waste your time moving your sub around the room looking for that “magic spot.” That’s for people who don’t have an equalizer for their sub. What they inevitably end up is response characteristics they can “live with” at the expense of extension and volume. Put the sub in a corner (one with maximum uninterrupted wall length in both directions). Of course, you will have one or two response peak, but after EQing you will have it all: the lowest extension, the highest SPL, and the smoothest response. Win, win, win!
    Hope this helps,
    Wayne A. Pflughaupt

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