Doctorchild, while technically correct, there are a lot of variables involved. How close the projectile passes to the ear, velocity, projectile size & direction it’s going, all affect the intensity of the shockwave & how it enters the ear. The bigger the projectile & the higher the velocity, the more intense the shockwave will be. The wave also looses pressure/intensity as it expands away from the path of flight, so how far from the ear the flight path is will affect the intensity also (not by much initially). The outer ear acts as a funnel, so the wave coming from the front or side will be channeled into the ear hole intensifying the effect, while coming from behind would tend to deflect much of it. Eardrums are like people & have different strengths, so that comes into play as well. It boils down to, it depends on all this whether the eardrum is broken or they just hear a loud crack, that may partially deafen them.
Slow & a lot of volume will work also. Cupping your palm & striking the ear will break an eardrum also. Doing both at the same time is a classic fighting move, if you want to seriously hurt someone fast.