Today I got my professionally calibrated microphone. Even without any correction files, it's only 0.5 dB off at 10 Hz. Pretty impressive. It was calibrated against B&K 4133 microphone.
I have now measured it against my analog RS meter. As I have said, the RCA output jack is weighted (C or A). But as Ethan showed, it appears that the output of the RCA jack of the digital RS meter is unweighted when set to C-weighting, when set to A, it's A-weighted. When set to C, it has a flat FR atleast down to 20 Hz.
Here is a TrueRTA screen of my results.
As you can see, even with those general CFs, the RS meter is still below the true FR. It tracks the mic down to 40 Hz, but below that it's off. You need to compensate even more than for example 7.5 dB @ 20 Hz. Around 11.5 dB seems to be more closer. Of course every RS is different, so this might not apply to your RS. Although me and my friends have measured total of three RS meters (analog) and they all give pretty similar FR.http://personal.inet.fi/private/ilkka/RS_calibrated.txt
Here is a calibration file which turns my RS into calibrated measurement microphone. When using this file its FR is within 1 dB (10 Hz - 200 Hz) from my calibrated microphone. It may not be as perfect with your RS, but much better than the general CFs. Notice that general CFs are way off below 15 Hz.Analog version:
Use atleast general CFs or this
file when measuring with the TrueRTA or smilar. Same thing if you are measuring manually (looking at the needle). You can use the rough corrections below, if you don't want to check the file (if you are measuring manually, add those corrections, do not subtract them).
Frequency / Correction
10 Hz +5 dB
12 Hz +6 dB
16 Hz +14.8 dB
20 Hz +11.5 dB
25 Hz +7.8 dB
30 Hz +5 dB
40 Hz +3.2 dB
50 Hz +2 dB
80 Hz +1 dB
100 Hz +1.2 dBDigital:
Do not use any correction files when measuring with TrueRTA or similar. The output of the RCA jack is unweighted when set to C-weighting. When measuring manually, add corrections shown above to the readings.