Mr. Karsten,
How, in layman's terms, would one go about "ringing" a cartridge with a square wave and observing the waveform? Are you talking about a special test record and an oscilloscope, or feeding an electrical signal (square wave)into the cartridge and viewing the returning signal?
Is this something that the manufacturer could do to give a precise recommended loading? I ask this because some manufacturers recommendations fall into a huge range (I believe my Lyra Titan came with a recommendation of 100 ohms to 47k ohms) while others give an incredibly precise figure, such as the loading recommendation for Allaerte cartridges.