Fixture for matching microphone capsules

This is a fixture I made to match Primo EM172 electret condenser microphone capsules for sensitivity. The speaker is driven by a pink noise signal and the mic capsule under test is recorded in Audacity, then a sample of the recording is analyzed for the rms level.
The mic capsules will be used to make a binaural mic to feed my Sony PCM-M10 digital recorder and some other peoples' projects at the Milwaukee Makerspace.