There are several Room Correction Software for recording studios, like Sonarworks Reference or IK Multimedia ARC. These manufacturers sell their own measurement microphones, and I’ve noticed that some are recommended to be used in horizontal position (pointing to the speakers) and others in vertical position (pointing to the ceiling). E.g.: the old version of the ARC microphone was recommended to be horizontal and the new one vertical.
What would be the correct position for the NTi MA220? I am using it with Sonarworks Reference 4 and with REW Room EQ Wizard.
free-field microphones should always point to the direction of a dominant sound source.
Therefore we definitly recommend the horizontal position (pointing to the speakers) for NTi Audio measurement microphones.
I'm not an expert but in my understading, these microphones are free-field equalized. So they should work in any direction. Hope the two pics help. You could also check their specifications yourself.