Dgad, I think the point is that one can alter the effective mass of the DV507 in the vertical plane, by using headshells of different weight mostly. I am not sure about iSanchez' idea that changing counter-weights has much of an effect on effective mass, especially if the counter-weight is decoupled, which it may or may not be in the case of the DV507. BTW, the manufacturer's spec for the effective mass of the DV507 is a fairly high 25 gm; that would be with the standard 15-gm headshell, no doubt. The XV-1s is said to have compliance of 10 X 10^6 cm/dyne, while the Urushi is said to have compliance of 10-12 "cu" or compliance units. I think 1 cu = 10^6 cm/dyne. Therefore, the two cartridges have about the same nominal compliance, according to their respective makers. In actual practice, there may be some differences, however, since compliance is frequency dependent and probably VTF dependent as well, and the two companies may have different ways of measuring. In the end, you have to determine for yourself where resonance is occurring in your own system, using a test record, as you say.