Apparatus is provided featuring a signal processor or signal processing module configured at least to: receive signaling containing information about a radiation impedance of a piston vibrating a process medium, including a fluid or slurry; and determine a speed of sound or density measurement related to the process medium, based at least partly on the signaling received. The signal processor or signal processing module may determine a speed of sound measurement related to the process medium, based on at least partly on the density of the process medium, including where the density of the process medium is known, assumed or determined by the signal processor or signal processing module, or determine a density measurement related to the process medium, based on at least partly on the speed at which sound travels in the process medium, including where the speed of sound of the process medium is known, assumed or determined by the signal processor or signal processing module.