  We numerically investigate sound damping in a model of granular materials in
two dimensions. We simulate evolution of standing waves in disordered
frictionless disks and analyze their damped oscillations by velocity
autocorrelation functions and power spectra. We control the strength of
inelastic interactions between the disks in contact to examine the effect of
energy dissipation on sound characteristics of disordered systems. Increasing
the strength of inelastic interactions, we find that (i) sound softening
vanishes and (ii) sound attenuation due to configurational disorder, i.e. the
Rayleigh scattering at low frequencies and disorder-induced broadening at high
frequencies, is completely dominated by the energy dissipation. Our findings
suggest that sound damping in granular media is determined by the interplay
between elastic heterogeneities and inelastic interactions.
