To improve tracking in the groove and achieve low distortion the mass of the cartridge parts that move the moving mass—must be lowered.
This can be done by removing the magnet from the rear of the cantilever (as in the moving magnet types) and substituting a tiny, very light, hollow piece of iron. The iron piece moves in the field of a stationary magnet, changing that field and generating a signal in the coil, Fig. 8.18.
As the armature moves toward or away from a stationary magnet pole, the reluctance (magnetic resistance) of the magnetic path changes. These cartridges are also referred to as variable-reluctance cartridges. The voltage generated is proportional to the rate of movement in the groove.
The advantages gained ...