  We consider the propagation of the piston mode in an acoustic waveguide
obstructed by two screens with small holes. In general, due to the features of
the geometry, almost no energy of the incident wave is transmitted through the
structure. The goal of this article is to show that tuning carefully the
distance between the two screens, which form a resonator, one can get almost
complete transmission. We obtain an explicit criterion, not so obvious to
intuit, for this phenomenon to happen. Numerical experiments illustrate the
analysis.
