A set of experiments is presented which allows one to obtain all the effects which appear as well in piezoelectric as in semiconducting and in semi‐insulating materials connected with acoustoelectric amplifaction, using only a single sample of CdS: a) the sequence of current‐steps, b) the various oscillation‐modes associated with them, c) the part of the boundary conditions (contacts) in the onset of these phenomena. Two sets of phenomenaaccording to the size of the onset time τ and its change with the temperature are distinguished. The behaviour of these two sets of phenomena allowing the presence of one or two acoustic fluxes in the sample from different sources is explained.