  A family of implicit-in-time mixed finite element schemes is presented for
the numerical approximation of the acoustic wave equation. The mixed space
discretization is based on the displacement form of the wave equation and the
time-stepping method employs a three-level one-parameter scheme. A rigorous
stability analysis is presented based on energy estimation and sharp stability
results are obtained. A convergence analysis is carried out and optimal a
priori $L^\infty(L^2)$ error estimates for both displacement and pressure are
derived.
