The second key difference between the 2 designs is that of inductance.
As Moving Coil cartridges have smaller coils than Moving Magnet cartridges, we can say that Moving Coil cartridges have a lower inductance.
Why is this important?
Because the inductance of the cartridge, the capacitance of the phono cable, and the resistance & capacitance of the phono preamp input altogether form a harmonic oscillator circuit, also called RLC circuit.
This kind of circuit has a ringing resonance at a certain frequency, and a steeproll-offof frequencies above the resonant point, also called low-pass filter. The lower the inductance of the coil is, the higher the frequency of the resonance is, and vice versa.
So for Moving Coil cartridges, the resonant frequency will be way up in the ultrasonic range, and changes of cable or phono input capacitance won’t have much of an audible impact. The ultrasonic ringing can also be damped by loading the cartridge with the appropriate resistance at phono input level.
With Moving Magnet cartridges, the higher inductance and capacitance will have an impact on the frequency response of the system in the audible range. For good Moving Magnet cartridges, the resonant frequency often falls somewhere in the top two octaves of the audible range, with all frequencies above that being rolled-off.
So to summarize: Moving Coil cartridges have a lower inductance than MM cartridges, so their frequency response is flatter and more extended. In comparison, Moving Magnet cartridges tend to have an odd frequency response, and a lack of high frequencies.
For stereo cartridges, smaller coils also means less crosstalk between them. As a result, MC cartridges tend to have better channel separation (+10dB or more) than MM cartridges. It translates acoustically into better stereo imaging.