  We consider boundary element methods where the Calder\'on projector is used
for the system matrix and boundary conditions are weakly imposed using a
particular variational boundary operator designed using techniques from
augmented Lagrangian methods. Regardless of the boundary conditions, both the
primal trace variable and the flux are approximated. We focus on the imposition
of Dirichlet conditions on the Helmholtz equation, and extend the analysis of
the Laplace problem from \emph{Boundary element methods with weakly imposed
boundary conditions} to this case. The theory is illustrated by a series of
numerical examples.
