I'm assuming the answer to this largely varies from person to person. Assuming you could instantly change the pressure around your head by amount $\Delta p$, what is the minimum $\Delta p$ for your ears to "pop" and adjust their inner pressure to the outside pressure?
I think the minimum building height that I have noticed this in is around 10 stories. Assuming 10 feet per story and $\Delta p = \rho g h$, the pressure difference comes out to about 0.05 psi.
What I'm asking is if there is some sort of "pressure release valve" in the ear that triggers for about the same pressure difference for most people?