If you look at the math, there is really quite a bit of leeway in effective mass and compliance that will give you a resonant frequency that falls within the typical range of 8 to 12Hz. And anyone who has done vinyl for a long time with a variety of cartridges and tonearms will tell you that you can get away with a slightly lower lower limit (lower than 8Hz, that is). The first reason is that the Fr is dependent upon the square root of the effective mass times the compliance. Taking the square root has the effect of blunting differences. (To understand what I mean, go on line and use one of the Fr calculators. Plug in some extreme values for M and C and note how relatively little that affects the results.) The second reason is that one really does not know and cannot easily know true accurate values for M and C for YOUR tonearm and YOUR cartridge, unless you empirically determine C and go through an arduous calculation for M, instead of using numbers given to us by the various manufacturers, which are average values at best. (I don't think every cartridge X has exactly the compliance that its manufacturer tells us it has, even out of the box, but especially if it is vintage or well used.) So, in the end, "just try it" is a good rule of thumb.
