All Norsonic microphones are free-field types. A free field microphone is designed to measure the sound pressure in the sound field, compensating for the influence of the presence of the microphone in the sound field. In effect, the microphone measures the sound pressure as it existed before the microphone was introduced in the sound field, i.e. free-field conditions.
Applicable standard is IEC 61672 and the former IEC 60651.
The free field microphone should be pointed towards the sound source at a 0° angle of incidence.