As a part of complex works aiming at the evaluation of the pump’s dynamic transfer matrix, this paper presents an estimation method of the speed of sound in water and water/air flows using three pressure transducers measurements. The experimental study was carried out at the CREMHyG acoustic test rig, for a void ratio varying from 0 to 1% and for amplitudes of speed of sound from 100 m/s to 1400 m/s. To estimate the speed of sound in this large range of amplitude, a new post treatment approach was developed, based on the least mean square method. Experimental results obtained were compared with existing theoretical models and a very good agreement was observed. The post processing appeared fast, robust and accurate for all the mono and diphasic flows analyzed. The results presented in this paper can be applied, for instance, in acoustic characterization of the hydraulic systems, mainly in the case of space rocket turbopump applications.