I am sure they will answer an english request. Let me know if you need help.Not enough for any practical conversation.
I use Line Audio Omni1. It is "good enough" without requiring a calibration file, and one of the best value performers for taking distortion measurements. Made in Sweden.
http://www.lineaudio.se/Omni1.html
Looks decent. But I already have uncalibrated dbx, which was similar price... Now I understand, that purchase of uncalibrated was a mistake.
Dbx provides no accuracy specification for the RTA mic, but some basic chart is provided here:
https://dbxpro.com/en/product_documents/rta-m_cutsheet-pdf
Thank you! Have seen this one - that visually "small" bump is pretty big, in the 4dB level - which is very likely true according to my measurements.
I have found also some .cal files on audio forums of the the same model microphone I am using, but they had very different curves, no such bumps.
What software would you recommend to build .cal file from scratch? Text editor?
I would assume, that it's intended use is for room EQ, where the frequencies of interest are <2kHz, so nonlinearity >5kHz is not incredibly important.
The opposite: I am most interested in all the range including up to 10-14kHz. It will be used to measure 2-way bookshelf speakers I am designing from scratch.