StopDropRoll, posted earlier a video of an experiment.
It shows the dynamics of an explosion inside of a real aircraft.
See in video at 3:03
https://youtu.be/Fi1_1l7M8FA?t=183
Notice the pressure gauge mounted near the cockpit. The pressure clearly increases before dropping.
The shock wave meets first the cabin pressure sensors, before to be heard in cockpit microphones(CVR). The FDR should show the cabin pressure increase.