  We study the dynamics of wave propagation in nominally diffusive samples by
solving the Bethe-Salpeter equation with recurrent scattering included in a
frequency-dependent vertex function, which renormalizes the mean free path of
the system. We calculate the renormalized time-dependent diffusion coefficient,
D(t), following pulsed excitation of the system. For cylindrical samples with
reflecting side walls and open ends, we observe a crossover in dynamics in the
transformation from a quasi-1D to a slab geometry implemented by varying the
ratio of the radius, R, to the length, L. Immediately after the peak of the
transmitted pulse, D(t) falls linearly with a nonuniversal slope that
approaches an asymptotic value for R/L>>1. The value of D(t) extrapolated to
t=0, depends only upon the dimensionless conductance g for R/L<<1 and upon kl
and L for R/L>>1, where k is the wave vector and l is the bare mean free path.
