There is a lack of consensus in the literature on the influence of the median particle size on stress wave velocity
in cohesionless soils. For assemblies of spherical particles with Hertzian contacts, the stress wave velocities
should not depend on particle size. However, a link between particle size and stress wave velocity has been
reported in laboratory experiments. In this study, to identify the reasons for the discrepancies, wave velocity
measurements were performed using planar piezoelectric transducers on four different sizes of alkaline glass
beads and natural silica sands. The experimental results indicate that shear and compression wave velocities are
independent of the median particle size. In accordance with dispersion theory, both the experiments and discrete
element simulations demonstrate that the maximum frequency that can propagate through a granular assembly
(i.e., the lowpass frequency) reduces with increasing median particle size. The relationship between the lowpass
frequency and the input signal frequency determines the quality of the received signal and hence the accuracy of
the interpreted stress wave velocity data. To accurately estimate shear wave velocities, the selected input
frequencies should match those frequencies which exhibit the largest gain factors and input frequencies should
not exceed the half of lowpass frequency. To determine the compression wave velocity, it is suggested to adopt
the start to start method and to choose an input frequency which is slightly lower than the lowpass frequency.