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A comparison of some measurement mics and pre-amps

a4eaudioa4eaudio
in DIY

I don't think there is much new or interesting to those who have been around awhile, but I did a little study comparing some mics and pre-amps. Partly for my own interest but also for those beginners who are thinking about getting measurement gear for the first time or maybe upgrading their measurement gear. (Dual channel only, no USB mics)

Its quite long (although mostly pictures) so here is the bottom line:
(1) A cheap mic is fine for crossover work as long as you have a good calibration file. But ensuring you have a good calibration file either requires decent money or getting a mic from somewhere like Cross Spectrum Labs or having someone with a reliable mic calibrate it. (A Behringer ECM8000 is $35 at Sweetwater but does NOT have a calibration file.)
(2) For accurate distortion measurements a cheap mic won't do
(3) A basic pre-amp with at least 96khz sampling rate is fine for crossover work. The best bargain I have found (not tested in the study) is probably the Behringer UMC202HD (especially an open box from Amazon Warehouse deals).

If you want to see the whole study it is HERE

Steve_Lee4thtry

Comments

  • tktrantktran

    Nice!

    I'm surprised the EMM-6 did so poorly on the distortion measurements...

  • a4eaudioa4eaudio

    @tktran said:
    Nice!

    I'm surprised the EMM-6 did so poorly on the distortion measurements...

    Yes, especially considering the rumors that it is exactly the same (probably coming off the same factory line) as the Behringer. I know PE was made aware of some of their poor calibration files, I wonder if distortion and/calibration have improved, but I'm not going to buy one just to find out.

  • Tom_STom_S

    It could have been a parts issue on a run of mics. Seems some of those overseas production houses will stamp part numbers on transistors that are deemed to be "close enough" to work in some circuits.

  • Ed_PerkinsEd_Perkins

    I know the quality of the ECM-8000 has been all of the map. I have an old one (~ 10 years) that CSL calibrated. Several years later their website stated they wouldn't calibrate ECM-8000s because their quality had deteriorated.

  • a4eaudioa4eaudio

    @Ed_Perkins said:
    I know the quality of the ECM-8000 has been all of the map. I have an old one (~ 10 years) that CSL calibrated. Several years later their website stated they wouldn't calibrate ECM-8000s because their quality had deteriorated.

    Yes, I remember that. The one I tested, which I just bought last year, tested pretty good. BUT...no calibration file. Did they ever come with a calibration file from Behringer or have they always been uncalibrated?

  • Tom_STom_S

    I don't remember the Behringer version ever having a Cal file.

  • tktrantktran
    edited May 29

    AFAIK, the early ECM8000 had the Panasonic WM61A capsule, up until ~2013 when Panasonic discontinued this unit. And they never came with a frequency response file.

    What capsule they are using now, I do not know.

    It's a shame Cross Spectrum Labs have paused their calibration service:
    "Shipping update (Apr 26, 2024): We apologize for the lack of updates. UMIK-1 mics are currently unavailable. A combination of health issues, equipment issues and project schedules have consumed the bulk of our energy as of late and we haven't had time to focus on microphones. We will continue to sell calibrated microphones and meters - we do have some units in stock that we haven't been able to process and offer for sale yet. We just need a little patience from everyone. Thanks for your understanding, and we'll provide further updates as we have them"
    **
    Reference:
    https://cross-spectrum.com/measurement/calibrated_umik.html**

    Although their calibration is using a substitution method (with their ACO Pacific 7052E capsule, as @a4eaudio has shown, this is good enough for DIYers, audiophiles, or people tuning their room acoustics etc. In essence turning a cheap electret condenser microphone, that may have swings of up to +/- 6dB:

    https://www.hifi-selbstbau.de/index.php/hsb-grundlagen/software-messtechnik/1000-mikrofonkalibrierungen-eine-uebersicht

    …to something that may be closer to +/- 1dB between 20Hz to 20Khz. This substitution method, of comparing one microphone to another, is in fact what Earthworks, iSEMCon and Sonarworks do for their microphones sold with individual "calibration" files or charts. They probably should call it frequency response charts, graphs or files, to avoid the confusion with calibration.

    Now, a Traceable Calibration is kind you could get when you purchase a measurement microphone from the likes of G.R.A.S., Bruel & Kjaer. This can be traced all the way back to the basic units eg. What is a decibel, what is a kilogram.

    The next step up in assurance is an Accredited Calibration. These kinds of things seemed to designed for Laboratory/ Scientific Instrumentation. They are related to supply chain certification and calibration and paperwork trails. And come from labs that have been accredited by the relevant national authorities...

    https://media.hbkworld.com/m/177c2768e6cbab1f/original/ISO-17025-Scope-and-Certificate-of-Accreditation-Duluth-2023.pdf

    Whether you need that level of precision or can tolerate that level of imprecision depends on what you're doing.

    FUN FACT: Did you know that the core body temperature is measured with a rectal or esophageal probe? (up a bum, down your throat?).

    Do you need that level of accuracy? Hmm, I'll take the ear (tympanic membrane) probe, which after conversion to theh oral (under the tongue) equivalent, is +/- 0.2 F/C.

    That's close enough, I'll take that please Doc!

    Now, if I was unconscious and in intensive care, that temperature probe best be Accredited...

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