Hi vanderghast, thank you very much for providing such a smart idea, and it seems quite practical and visualized.It is possible that a human activity enters in vertical resonance with the structure. A "well known" case is given, for a 39 story building at https://www.sciencedirect.com/science/article/pii/S0141029613004471
You should be able to measure the frequency with a laser beam light fixed on the wall (the wall is assumed to be "fix") with the laser beam ray as parallel as possible to the floor, but hitting it at it middle long span (if you prefer, have the laser beam as low as possible but intercepting the middle of the floor). The intersection of almost two parallel lines (the floor and the laser ray) is highly dependent of the exact slope of either line. So, under a floor in vibration, you should be able to see the laser spot on the floor moving back and forth the center of the floor. You should so be able to get the frequency with a light detector (the laser hitting and leaving to hit again, moment later, the light detector), or counting the frames from a movie you would have recorded, having the frame rate of the camera.
In order to document the issue you might want to try one of the vibration monitoring apps. Some of them can record data so you could get the frequency and time for the vibrations.
Thanks for your attention. I also tried several vibration monitoring apps, and have recorded data by using some of them.I just installed one. Surprisingly sensitive. Picked up me tapping my foot while the phone was on the table.
diapason
What would you connect this to? I am thinking of a different type application like to prove there are 3 people not 1 living next to me which is why my vibration issue is 24/7 and that Im not going insane and hearing voices that speak a foreign language when the neighbor on the least is not home. Sorry if you read my reply to the just of the original thread this will make better sense..Thx PieperA PZM microphone + recording in Audacity has to work well.
On a side note thanks for asking. Wife is doing OK overall. Like most cancer we get a step forward and then a step backwards.