I've been wanting to try out a cardiod in my MS setup (MKH30&50/60) to get a better image. But instead of buying a MKH(80)40 i'm trying out Line audio cm3's. They are nice mic's for a very low price and sound pretty good. The sensitivity is much lower (6mv/Pa) compared to the MKH30(25/Pa).
So I tried to match sensitivity by A-B ing the MKH50 and CM3. This showed a 6.21dB difference in favour of the MKH50. I did some test recordings with both mics ganged to the gain of the MKH30. The idea was that in post i could easily add the 6.21dB to the Mid channel (CM3) and get a good stereo image after MS matrixing.
However, back in the studio I ran into some difficulties. Some recordings were fine and others not (phase issues and extreme wide stereo image). So i thought, I must be able to calculate the difference. I searched the archive and found this post: What do sensitivity measurements of microphones really mean? Following this formula I reached almost the same result, a 6.19dB difference. So great, I was close in my test, but why is one recording good and another not?
Now I'm thinking something is wrong with my train of thought. Could it perhaps be that when I use more or less gain the sensitivity ratio (25:6) is influencing the output differently?
I didn't take note of the preamp gains so I don't know if this had any influence. I will continue my tests, but maybe somebody here has a more academic/technical approach?
Thanks in advance!