The alterations of the resonance frequency of the vibrating tip of an acoustic sensor detect the density and the viscosity of liquids. The employed acoustic near-field sensor has several resonance frequencies which correspond to its different parts. We determined that the resonance of the body of the acoustic sensor is sensitive to the rheological characteristics of viscoelastic media. We carried out experiments with bitumens and we modified the acoustic load on the sensor in two ways: the immersion depth of the tip and the temperature of the bitumen specimens. Theoretical and experimental results are compared.