sound source localization - calculation of sound intensity vector angles
So this technique approximates the velocity of the particles using the pressure gradient at a time instance. This approach is only correct for microphones that are spaced closely together. The max frequency it can measure correctly with the spacer we're using is around 4.8kHz (stated in datasheet), so all angles corresponding to higher frequencies gave a wrong answer. This caused the 180 degree shifted angles.
A great explanation/visualisation from Siemens can be found here