The Barkhausen noise power spectrum was investigated on laminated polycrystalline toroids of Fe and 4% SiFe as a function of sample thickness; that is, of surface-to-volume ratio. Upon decreasing the thickness strong variations of spectrum shape are observed-the cut-off frequency increases and the spectral density drops in the very-low-frequency range. On the other hand, only negligible variations of static magnetic properties are observed. According to a recent theory, the results are explained assuming that a change of thickness directly affects the number of elementary pulses clustering into a large Barkhausen discontinuity. The calculated variations of the spectrum intensity and cut-off frequency are in good agreement with the experimental results.