NTI M2010 class 1 measurement microphone

There has been some discussion in the past on getting B&K or other high quality metal diaphragm mic cartridges to work with non-proprietary audio interfaces. Generally, these systems have odd connectors, require odd power supply voltages. and would require significant DIYing to work with standard USB audio interfaces. While digging around online I discovered the NTI M2010 microphone has a very nice ACO Pacific 7052 metal cartridge, and also has a standard 48V phantom power XLR input. The retail price is $1395, but there happens to be a surplus place in Canada selling a mountain of them for ~$255 ea. on fleabay at current exchange rates.

I called NTI and the rep told me the mic will work with a standard audio interface. He also said they can provide the original factory calibration data by email on request. He said that data should still be valid after many years, assuming the mic hasn't been "knocked around." Alternatively the mic could be calibrated at CSL ($60) or Scantek ($175).

This seems to me like an attractive option for a measurement microphone. Even with precision calibration from Scantek the cost of a used mic in competitive with mics like the Earthworks M23 or iSemcon. Thoughts?
 
Below is a plot of my calibration files. No data above 20 kHz was provided by NTI.
1713827497545.png
 
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@jhenderson01075

I note that you have two samples with the same serial number of 3727- Is this is a typo?

In combination with 1 other user @ ASR, thanks to your data, we now have 6 random samples of the NTI M2010.
They are all within +/- 0.5dB from 20Hz to 2KHz.
Above 2KHz, they have slightly higher deviation.
I've auto-traced and plotted these 6 samples on one graph, and also the mean deviation (red)

1713831544362.png


My hypothesis is that these tweeters have useful ultrasonic response above 20KHz. This undocumented feature may serve useful for people working / designing with hard dome tweeters:

eg. The same aluminium dome tweeter measured by 3 different microphones: Umik-1 (red), Sonarworks Xref20 (light blue), Earthworks (blue).
All microphones are calibrated by their manufacturers to their specified limits, but only 1 microphone shows the high peaky resonance of this tweeter, which would benefit from a correctly implemented notch filter.

1713831872281.png




Thanks to other users @Joseph Crowe & @DcibeL we should be able to confirm in the coming weeks whether this NTI M2010 has usable response to 40-50KHz.
 
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