The mechanisms of sound attenuation are different in dispersions with
low and high density contrast. ''Viscous losses'' are dominant in high
density contrast dispersions whereas ''thermal losses'' predominate i
n dispersions with low density contrast, The rutile dispersion is chos
en as an instance of the high density contrast system. The dispersion
of the neoprene latex is an instance of the low density contrast syste
m, The dilution experiment performed with both systems shows that the
role of the particle-particle interaction is quite different in these
two dispersions. The measured spectra show that attenuation remains a
linear function of the volume fraction in the latex dispersion even at
30 vol %. At the same time, attenuation exhibits a nonlinear dependen
ce on the volume fraction for the rutile dispersion even at 10 vol %.
This difference means that particle-particle interaction contributes m
ore to the ''viscous losses'' than to the ''thermal losses'', We assoc
iate this effect with the difference between ''viscous depth'' and ''t
hermal depth'' These parameters characterize the penetration of the sh
ear wave or thermal wave into the liquid. The observed insensitivity o
f the thermal losses to the particle-particle interaction supports the
application of dilute case theory to calculate the particle size dist
ribution in the concentrated (up to 30 vol %) emulsions and latices.