Cartridge Loading and Compliance Laws

I wasnt making a general statement that a heavy arm is better. I was just trying to think through the variables and it seemed that a heavier arm would do the things an arm is supposed to do better than a lighter arm. I dont know if that is true, however, since I havent been able to hear and compare the universe of arms out there. My thoughts were just that I seem to hear a mantra of heavy arm = low compliance cartridge, light arm = high compliance cartridge and was questioning whether that is true. Again, I dont know and only seek to understand and learn.

"heavy arm = low compliance cartridge, light arm = high compliance cartridge"
Yes, that is a mantra of the internet that I read very often, too. As I am sure you know, that formula is meant to set the low frequency resonance at a frequency between 8 Hz (so as not to excite resonance via footfalls and other very low frequency sources) and 12 Hz (so as to stay away from the audio bandwidth). The formula for that resonant frequency can be found on Vinyl Asylum and in other places, but tonearm effective mass and cartridge compliance are its principle determinants. So this is why the gurus tell us, "heavy arm = low compliance, etc". However, there are guys on this discussion group, most notably Raul, who point out that there are many other factors that determine the overall "goodness" of a match between tonearm and cartridge and that sometimes one can and should overlook the mantra in search of good sound. One example is that several owners of the Fidelity Research FR66, a 12-inch arm with very very high effective mass, claim it sounds fantastic with MM and MI cartridges that have very high compliance. Conversely, some others who own very light tonearms like the ADC and the Black Widow like to use them with MC cartridges that have low compliance. To all this I say, "go figure". The take home lesson I think is if you have a tonearm you like a lot, don't stop using it just because it might technically be a mismatch with your new cartridge, on the basis of its effective mass vs the cartridge compliance. All bets are off.

Why this is true is worthy of another separate discussion, but I have my ideas.

And those ideas are...?

Another thing, I have often wondered about is - does it really matter if you use washers under the cartridge screws? I know it adds a little weight but is it a bad idea from a sonic perspective? Thoughts anyone??

Depends on the washer... a nylon washer should probably be avoided- the coupling between the cartridge and arm should be as tight as possible, and nylon will squish.