The acoustic near field method consists in studying the alteration of the resonance curve of a horn whose tip, the probe, is immersed in the sample. The operating mode in a medium in which strong variations of the rheological properties take place, is modelled for two horn shapes, one with a conical probe, the second one with a stepped cylindrical probe. The experimental curves obtained during the cement setting prove the validity of the simulations. The sensitivity of the horn to a given step of the setting is achieved by adjusting the probe shape.