The effect of experimental variables upon the damping characteristics of particulate materials was investigated using the low intensity vibration method (Yanagida et al., 2003) of the present series of papers. The loss factor was measured from the acceleration transmissibility data. A significant stress dependence upon the elastic modulus was seen, whereas the loss factor showed the insensitivity to experimental variables including the compressive stress, the particle size and the bed height within the range of this study. A model based upon fundamental contact mechanics gave a qualitative interpretation for the insensitivity of the loss factor at small amplitudes.