Two models of calculating the association constants in mixtures of two weakly interacting liquids are proposed and analyzed: one of them assumes additivity of acoustic impedance with the molar fractions of components, and the other assumes additivity of the time of transmission of the acoustic signal with the volume fractions. The models were tested for different systems, showing that the latter yields results much more reliable and closer to expectations. The presented attempt seems to be an interesting alternative way in interpreting the experimental results of sound velocity measurements in liquid mixtures. (C) 2003 American Institute of Physics.