The effect of a body changing its dimensions while applying a magnetic field or changing its state of magnetization is called magnetostriction. The basis for this mechanical deformation is the interaction between the external magnetic field and the elementary magnets formed by the atoms circled by electrons. The evidence of this effect depends on the crystalline structure of the material and the elements containing. The effect is mainly marked in ferromagnetic materials.
Concerning an electrical contact, the quality of which is mainly achieved by contact pressure, magnetostrictively caused, as result of the alternating magnetic field of the current of a loudspeaker for instance, changes of geometry would directly modulate the transmitted signal by the alternating transition resistance.