Abstract: The process comprises injecting, before the polystyrene expanding stage, high-pressure steam into a mould which forms the definitive shape of the ribbed and grooved surface of a blank of the diaphragm. After removal of the blank from the mould, water is made to travel toward the ribbed and grooved surface of the blank by condensation resulting from a lowering of the temperature. The blank is then brutally frozen so as to produce microfractures in a thin superficial zone of the blank. This superficial zone is removed by means of a suitable machining operation so as to expose under this zone the softened aspect of the diaphragm immediately subjacent to this zone.Application in the manufacture of electrodynamic loudspeakers.