Is cartridge Demagnetizing Necessary?

Just don’t demagnetize a moving magnet cartridge, or you will have no magnet and no cartridge. The rest of it is up to you. I would never use a demagnetizer per se. I occasionally use the tracks on the Cardas test record which are specifically for demagnetizing.

Ironically, there is a business centered around routing the audio signal thru cables surrounded by powerful magnets. Go figure.

lewm

Just don’t demagnetize a moving magnet cartridge, or you will have no magnet and no cartridge.

This is completely mistaken.
MM cartridges can be safely demagnetized - see the instruction manual for details. The Sumiko Fluxbuster manual specifically cautions against demagnetizing MM cartridges until the stylus assembly is removed first.

OK. Everyone should read the Sumiko Fluxbuster manual, because after all they have no agenda in the debate.  Bust all the flux you want.

1+++lewm. The entire concept of "demagnetizing" a cartridge is beyond silly. The only thing you can hope to do with a real demagnetizer (like we use to use on tape heads) is ruin the cartridge. This is a typical example of audiophile mythology because it seems many audiophiles are not able to determine what is real and what is illusion. 

Uh oh.   

On the one hand yes, using a demagnetizer on a cartridge is a bad idea because there's magnets in there and we do not want to mess with those. We only want to demagnetize the wire. Not the magnets. Just the wire.  

The wire itself we demagnetize by running a signal through it. That is what the demagnetizing tracks on the XLO and other CDs do. The theory of how it works and the fact that it does indeed work has already been explained quite clearly above and will not be repeated here. Anyone genuinely interested in trying to understand, simply scroll up and read the posts.  

Only thing worth adding is the Cardas Test Record works the same way, sweep/fade type signal, with the advantage it would do not only the cartridge but the phono leads and phono stage as well. Just haven't tried it myself to know how good it works.