An investigation into the acoustic noise produced by the ferrite core used in television line output transformers

Details are given of the measurement of the acoustic noise produced by a line output transformer and polar diagrams are shown of the sound pressure around the core. It is shown that in the region of the television line frequency, 10.125 kc/s, the core can resonate in a flexural mode giving extreme levels of noise. A detailed analysis is given of the radiation diagrams produced from a vibrating face of the core and from this information the relationship between flux densityBand fundamental strain is found. Methods of clamping and glueing the core are suggested in order to reduce the noise from the core due to flexural resonance. Finally, attention is drawn to new materials developed in conjunction with this work, which produce very little magnetostrictive strain over the flux density range in which the core is operated. Measured results of flux density against fundamental strain are given for these materials and existing materials.