I've put EM 172 microphones inside Steve's isolation box to measure their noise. I've attached mics to each other and aligned them using the tape.
At low frequencies (below 1 Hz) the noise is limited by ADC as there is a 10 Hz high-pass filter inside mic readout box.
ADC noise is measured by splitting the signal from 1 mic into 2 ADC channels.
BT EM172 microphones are ordered.