  In this paper, we consider an open tube of diameter $\epsilon>0$, on the side
of which a small hole of size $\epsilon^2$ is pierced. The resonances of this
tube correspond to the eigenvalues of the Laplacian operator with homogeneous
Neumann condition on the inner surface of the tube and Dirichlet one the open
parts of the tube. We show that this spectrum converges when $\epsilon$ goes to
0 to the spectrum of an explicit one-dimensional operator. At a first order of
approximation, the limit spectrum describes the note produced by a flute, for
which one of its holes is open.
