KM184 off-axis response and ORTF
Author: Lutz Schmidt
Date: 06/09/2011
Hello everyone!

I ran into an issue recently when recording a choir with KM184's in ORTF. I have to say that I never recorded a choir before.
To the largest part, everything went as desired: good location, the group was not too large (about 40), placed as a kind of semi-circle , female voices placed towards both sides; the stereo imaging was nicely balanced with good depth.

Occasionally, female sibilants (esses) from either side blended into the other channel, smearing the stereo localization and shifting the image towards the center.
I had no idea what might have caused this until I saw the 90° off-axis response curve of a KM140 quite recently. I assume that the design of the capules of a KM140 and a KM184 is basically identical?
For that KM140, the 90° off-axis resonse showed a +3dB peak around approx. 9kHz whilst the on-axis response showed a small dip at the same frequency. The 0°and 90° sensitivities matched at this point.
(Microphones of other quality brands showed rather similar characteristics.)
This means to me that under those specific circumstances, for an "ess" with a lot of energy around those 9kHz, arriving from let's say 40°-60° off-axis, there is diminished channel separation. The time difference of ORTF will have no real effect here.

I am not absolutely sure if I am right with this? Any suggestions or comments would be appreciated.
Lutz Schmidt
Martin Schneider/Neumann
Baptist Clauwens
Uwe Sattler/NeumannUSA
John Willett
Uwe Sattler/NeumannUSA