Frank, , the term "compliance" relates to the flexibility of the suspension of the particular cartridge. Generally, a number of 12cu or under is considered low compliance. Low compliance means a stiff suspension, and often accompanies a heavier cartridge. Over 12 and under about 25 is medium. And over 25 is high compliance. Actual numerical values of these definitions may vary by some opinions, but these are approximately the values.
Many observe the proper guidelines for arm/cart resonance matching, which would give a combined mass/resonance in the 10Hz-12Hz area. But this is not the only thing that needs to be accounted for. Compliance will affect some tonearm designs in different ways. For example, you don't put a super-high compliance cart on a high mass tonearm. You don't put a super-low compliance cart on a low mass tonearm.
What I referred to above was low compliance incompatibility with certain unipivots. The lack of rigid horizontal orientation of these arms precludes use of very low compliance carts, due to the propensity of the cartridge compliance to cause the tonearm to change azimuth during play. Outriggers and fluid damping, and higher weight "cups" have mitigated this somewhat in the better designs, but the basic rule holds in the more extreme cases. All unipivot designers are aware of this, and readily admit this mismatch with low compliance carts. I even recently read an interview with Harry Weisfeld, the designer of the JMW arms, and when asked about the disadvantages of unipivot tonearms,he said in the interview," as the arm rides up and down on the record, the aspect ratio can change. In other words the arm tilts."
This is not much of a problem with medium and high compliance cartridges, because they do not generate the same amount of deflection to the arm as a low compliance does. So, the result is that medium and higher compliance carts are better matches for these types of arms than low compliance ones.
Very low compliance carts like the Denon DL103, present a challenge to even the better gimbal-bearing arms, due to the energy transmitted to the arm and bearings.
In the case of a "borderline" match, where the numbers are on the edge of compatibility, it is potentially a problem. You should not go there unless you are willing to sell the cart or the arm in case of a mismatch.
For a rookie, the best bet is stay in the "happy medium". A medium mass arm, a medium compliance cart, will usually provide good results. When you start to get into the exotic stuff, you should have gained enough knowledge and experience to make the correct matching decisions.
That was a copy of one of my previous posts in the archives on this subject. To address your particular question about arm masses and examples, generally under 7 grams is lightweight, 7-11 grams is medium weight, and 12 or over is heavy weight. Again, these are generalizations, but they are pretty accurate. Like a Rega tonearm with 11 grams effective mass is on the high end of "medium" and could be used with a lower compliance cartridge in many cases. Most arm manufacturers will give the effective mass spec on their spec chart for the arm. You can compare that to my generalizations above for the category it would fall under. There are also some charts on the net, that I couldn't find just now, that give resonance matching data.
For some examples of arm types, a Rega is a gimbal-bearing arm, a Graham or JMW would be examples of unipivot arms. And of course, an ET-2.5 is an example of a linear tracking arm.
I hope that helps you out.
