A probe 10,170 is provided that measures the speed of sound and/or vortical disturbances propagating in a single phase fluid flow and/or multiphase mixture to determine parameters, such as mixture quality, particle size, vapor/mass ratio, liquid/vapor ratio, mass flow rate, enthalpy and volumetric flow rate of the flow in a pipe or unconfined space, for example, using acoustic and/or dynamic pressures. The probe includes a spatial array of unsteady pressure sensors 15-18 placed at predetermined axial locations x.sub.1-x.sub.N disposed axially along a tube 14. For measuring at least one parameter of a saturated vapor/liquid mixture 12, such as steam, flowing in the tube 14. The pressure sensors 15-18 provide acoustic pressure signals P.sub.1(t)-P.sub.N(t) to a signal processing unit 30 which determines the speed of sound a.sub.mix propagating through of the saturated vapor/liquid mixture 12 in the tube 14 using acoustic spatial array signal processing techniques. Frequency based sound speed is determined utilizing a dispersion model to determine the parameters of interest.