We knew that there will be clockdrifts and synchronization problems between the boards, because they were not connected to a central word clock (this was a hardware-restriction).
we set up the 24element circular array in a way that eight MEMS microphones connected to one board represent an 8-element circular array with constant angular interval of 45 • ; considering all three circular arrays, the merged 24-element circular array exhibits an interval of 15 • .