  Calculation of the effective quasistatic shear speed $c$ in 2D solid phononic
crystals is analyzed. The plane-wave expansion (PWE) and the monodromy-matrix
(MM) methods are considered. For each method, the stepwise sequence of upper
and lower bounds is obtained which monotonically converges to the exact value
of $c$. It is proved that the two-sided MM bounds of $c$ are tighter and their
convergence to $c$ is uniformly faster than that of the PWE bounds. Examples of
the PWE and MM bounds of effective speed versus concentration of high-contrast
inclusions are demonstrated.
