  We show some new properties of the acoustic propagation in two-dimensional
sonic crystals, formed by parallel rigid cylinders placed in air. The
transmission through slabs of sonic crystals and the associated band structures
are considered. It is shown that within partial bandgaps, the waves tend to be
collimated or guided into the direction in which the propagation is allowed.
Such a feature also prevails in the situations in which deaf bands appear. We
show that within the partial bandgaps, a stable imaging effect can be obtained
for flat sonic crystal slabs, in analogy to the cases with photonic crystals.
