  In this work we have developed a technique for the measurement of the
resonance curve of Helmholtz resonators as a function of filling with beads and
sands of different sizes, and water as the reference. Our measurements allowed
us to observe very different behaviors of resonance frequencies and resonance
half-widths as a function of the size of the sand grains and the beads. By
comparing results for beads and water we were able to prove that the sound
penetrates the interstitial space between the beads. This was confirmed by
measurements of the resonance properties in resonators filled with spherical
beads whose experimentally determined filling factor is close to the random
filling factor of about 0.54. The similar behavior of the frequency and
half-width of resonance of sand-filled resonators of three different sizes
allowed us to suggest that sound penetrates the sand in the same way as it does
the beads.
