One effect of putting a crystal, or anything with mass, on a tonearm or cartridge is to alter the... mass. This can always be expected to have an effect of some kind. So, on that basis alone, no wonder it is common to hear a "difference". Has anyone done the following control?: Take a pebble or something of equal mass and affix it where you have previously heard a difference with the crystal. Then play a record and listen. On other grounds, I have come to think that most low compliance LOMCs can benefit sonically from an increase in tonearm effective mass, compared to the effective mass of the typical modern high-end tonearm, most of which are medium mass, at best. Just a thought.