To open up the bottom part you'll have to remove both "grills" from the front (lots of adhesive tape) and loosen the screws - two T5 for the top plus four PH1 screws hidden beneath another layer of black adhesive for the bottom grill.

Then remove the hinge (pull axis outwards), I've also removed the bottom plate (two screws plus clipped near the lengthy holes).

Then the front and back part can be slowly pulled away (mine were held by glue holding mics on place), beware the two pins at the bottom, and start at one far end, things should come loose soon. Maybe one need to get a tweezer in the small hole at the front ends to help a clip come off, but starting at one end, going thhrough middle part and then the other end was fine for me.

Nothing special here, four mics plus a small PCB holding two WM8737G (stereo ADC) providing 4 channels PCM audio.