Sorrodje's mic calibration gadget loaner (US & EU)

Discussion in 'Closed Loaners' started by sphinxvc, Nov 11, 2016.

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  1. sorrodje

    sorrodje Carla Bruni's other lover - Friend

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  2. stratocaster

    stratocaster Friend

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  3. Serious

    Serious Inquisitive Frequency Response Plot

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    Just received it. Am I right in assuming that @landroni is next and then it finally goes back to @sorrodje?
     
  4. MrButchi

    MrButchi Gear Master Europe

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    Afaik, yes!
     
  5. Serious

    Serious Inquisitive Frequency Response Plot

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    Sent the package out to @landroni today.
    Overall it was a pretty useful device. My UMIK calibration file had the sensitivity set to -2.5, but according to the calibrator it was about +0.5. I used a piece of tape to seal the mic like how @atomicbob recommended. I also appreciated that he included the adapter he made for 1/4" mics. I used it for my WM-61A.

    One thing to keep in mind is that the air pressure will change the calibration. I think it was something like -0.1db for every 25 mbar less than 1013, but I can't quite remember. It's in the manual. (This actually seems like a lot to me. Dunno if the more expensive stuff is better in this regard.)
    There was some variation for the calibration. Use the SPL logger in REW to get readings to 0.001db accuracy. I found that there was some variation when turning it off and on again.

    I want to check against my speaker sensitivity again. I really wonder why the UMIK would be 3db less sensitive than the calibration file.
     
  6. atomicbob

    atomicbob dScope Yoda

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    You have hit upon why the Bruel & Kjaer 4231 is $2000 and not $120 like the ND9. Compensation for temperature, air pressure, battery voltage, aging, slight variance in mic cavity due to variance in mic capsule sizes, etc. Over the years my 4231 has varied only 0.1 dB in calibration cycles with Scantek. Measurement repeatability of less than 1 dB is considered very good in the acoustic world. It is very hard to achieve 0.1 dB repeatability like is more easily obtained in electrical measurements.
     
  7. sorrodje

    sorrodje Carla Bruni's other lover - Friend

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    in our use ( amateurish headphones meausurements) I don't think we need such a precise calibration. At least the ND9 allows to check if our mic/setting/procedure is not completely wrong and that's why I bought it.
     
  8. atomicbob

    atomicbob dScope Yoda

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    Of course. I carry an ND9 into a lot of my field work. Most of the time it is to verify that nothing has changed dramatically or very easy adjustment of preamp gain stage. Standard dual system tape measures are preferable to carrying Starett Heavy Spring Tempered 1 meter Precision steel rule ($300 US) as an analogy. And for +/- 1~2 dB calibration the ND9 is an excellent choice.
     
  9. landroni

    landroni Friend

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    Got the package, thanks! Where do I ship it next?
     
  10. sorrodje

    sorrodje Carla Bruni's other lover - Friend

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  11. landroni

    landroni Friend

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    I'm now playing with the ND9 -- cool gizmo.

    Two questions to the experts:
    - when you couple the mic with the calibrator, do you remove the foam from the mic? I suspect 'yes', but I'm new to the game...
    - with the foam removed, when you couple the two do you slightly push them against each other to improve seal, or do you seal them as well as you can and then leave them stand freely on the table? The difference between both techniques is barely 0.1 dB, so I guess this is more academic than anything.

    Either way, what I did was remove the foam and couple by gently pushing the ND9 against my DL1351. The results:
    As found: 92.7 and 112.8 dBA
    As left: 94.0 and 114.1 dBA

    [​IMG]
     
  12. atomicbob

    atomicbob dScope Yoda

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    @landroni
    1. yes, foam MUST be removed.
    2. tight seal provides best results. I use gaffers' tape to make a shim for this when wanting best precision. However, for this level of work I will often do exactly as shown in your picture, including the mouse pad(s) for alignment.

    Your results are in alignment with what I typically see for this type of device. Well done.
     
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