How do scientists know how acoustics work?

I've seen lot of theory about how it works.
But how do they get to that conclusion?
As far a i know, you can see that it's air vibrating bc when there's a loud noise you can feel the floor vibrating or if i drop something in a table and i place my hand on it i can feel the table vibrating as well. But how do they know it in more detail. How do they know about the pith and that it's a wave?