A mechanical agitation-free method of making a homogeneous mixture of polyvinyl chloride solids and at least one liquid additive and/or particulate solid additive without mechanically-agitating or melting the polyvinyl chloride solids during the making. The method comprises applying acoustic energy at a frequency of from 20 to 100 hertz to a heterogeneous mixture comprising the polyvinyl chloride solids and the liquid additive and/or particulate solid additive for a period of time sufficient to substantially intermix the polyvinyl chloride solids and the liquid additive and/or particulate solid additive, while maintaining temperature of the heterogeneous mixture above the freezing point of the liquid additive, below the melting point of the particulate solid additive, and below the melting temperature of the polyvinyl chloride solids, thereby making the homogeneous mixture without mechanically-agitating or melting the polyvinyl chloride solids.