  Mechanical impulse propagation in granular media depends strongly on the
imposed confinement conditions. In this work, the propagation of sound in a
granular packing contained by flexible walls that enable confinement under
hydrostatic pressure conditions is investigated. This configuration also allows
the form of the input impulse to be controlled by means of an instrumented
impact pendulum. The main characteristics of mechan- ical wave propagation are
analyzed, and it is found that the wave speed as function of the wave amplitude
of the propagating pulse obeys the predictions of the Hertz contact law. Upon
increasing the confinement pressure, a continuous transition from nonlinear to
linear propagation is observed. Our results show that in the low-confinement
regime, the attenuation increases with an increasing impulse amplitude for
nonlinear pulses, whereas it is a weak function of the confinement pressure for
linear waves.
