This work describes a simple apparatus used to measure power spectra of Barkhausen noise in an analysis frequency band between 25 and 104 cps. Because previous work by the authors showed that when the specimen is in the form of a closed magnetic circuit and unlaminated the intensity of the noise has but small dependence on the core dimensions, unlaminated ring-shaped samples were used in this work. Spectra obtained with a magnetizing field frequency of 0.1 cps are given for iron, 6% silicon iron, grain-oriented silicon iron, ultraperm, mumental, nickel, and Permalloy C. It is observed that the intensity of the noise depends to a large extent on the nature of the ferromagnetic material. No interpretation of this fact is given, as it appears very complicated to understand.

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