The tonearm has a number of tasks to perform. First, the bearing must low in friction to allow for free movement of the cartidge but rigid enought so that vibration imparted by the stylus movement to the body of the cartridge does not cause the arm to rattle around. A good arm both dampens such vibrational energy within the arm as well as transmits energy down the arm to be dissipated elsewhere (such as in the armboard) rather than allowing that energy to be fed back to the cartridge.
Because no arm can be perfect at eliminating the effects of vibrational energy, the arm should also be matched to the particular cartridge to minimize the adverse effects of such energy. The "effective mass" of the arm and cartridge should be matched to the "compliance" of the cartridge suspension so that the resonant frequency is in a range that does not cause problems. For example, a high compliance cartridge should not be matched to a high mass arm. You will find that such matching can be a complex subject with some disagreement on what is ideal. There are some arms that are deliberately designed to have high mass in the horizontal plane (movement side to side) and low mass in the vertical plane (up and down); this is done to deliberately make the arm less responsive to side to side forces imparted by the cartrdige tracking bass notes so that the cartridge itself does not move in response to the groove undulations (meaning bigger movement of the stylus itself and more bass).
The arm should be adjustable enough to allow for ideal alignment of the cartridge to get the best performance from the cartridge. Some arms make this much easier to accomplish than others, althoug "ease" does not necessarily mean that ultimate accuracy is higher.
At a minimum, a good arm will allow the cartridge to "track" the groove such that there will not be gross distortion from the stylus losing proper contact with the walls of the groove. This can happen on very active passages, meaning loud passages, or passages with a lot of high frequency energy (such as the sibilant energy of a singer getting too close to a microphone) or passages with very powerful bass notes. Better arms, and arms that are a better match to a particular cartridge, will allow the cartridge to perform up to its full capability in this respect.
There is, like everything else in audio, the important matter of personal taste. The sound of each particular arm/cartridge combination will be different in some respects and what is preferable depends on system matching and personal taste. As I mentioned above, effective dampening of vibrational energy is generally a good thing, but, some listeners will complain that a particular arm makes their cartridge sound dead and lifeless. This could be the result of such high degree of dampening.
Because it is not realistically possible to try all sorts of different arms in one's system before making a purchase, to some extent, getting the "right" arm, is a matter of luck or getting good advice. As a gross generalization, I would say that all of the high-end arms that have a good reputation will perform better than run of the mill arms, but, when you get up into picking among such arms, it is mostly a matter of taste.
Because no arm can be perfect at eliminating the effects of vibrational energy, the arm should also be matched to the particular cartridge to minimize the adverse effects of such energy. The "effective mass" of the arm and cartridge should be matched to the "compliance" of the cartridge suspension so that the resonant frequency is in a range that does not cause problems. For example, a high compliance cartridge should not be matched to a high mass arm. You will find that such matching can be a complex subject with some disagreement on what is ideal. There are some arms that are deliberately designed to have high mass in the horizontal plane (movement side to side) and low mass in the vertical plane (up and down); this is done to deliberately make the arm less responsive to side to side forces imparted by the cartrdige tracking bass notes so that the cartridge itself does not move in response to the groove undulations (meaning bigger movement of the stylus itself and more bass).
The arm should be adjustable enough to allow for ideal alignment of the cartridge to get the best performance from the cartridge. Some arms make this much easier to accomplish than others, althoug "ease" does not necessarily mean that ultimate accuracy is higher.
At a minimum, a good arm will allow the cartridge to "track" the groove such that there will not be gross distortion from the stylus losing proper contact with the walls of the groove. This can happen on very active passages, meaning loud passages, or passages with a lot of high frequency energy (such as the sibilant energy of a singer getting too close to a microphone) or passages with very powerful bass notes. Better arms, and arms that are a better match to a particular cartridge, will allow the cartridge to perform up to its full capability in this respect.
There is, like everything else in audio, the important matter of personal taste. The sound of each particular arm/cartridge combination will be different in some respects and what is preferable depends on system matching and personal taste. As I mentioned above, effective dampening of vibrational energy is generally a good thing, but, some listeners will complain that a particular arm makes their cartridge sound dead and lifeless. This could be the result of such high degree of dampening.
Because it is not realistically possible to try all sorts of different arms in one's system before making a purchase, to some extent, getting the "right" arm, is a matter of luck or getting good advice. As a gross generalization, I would say that all of the high-end arms that have a good reputation will perform better than run of the mill arms, but, when you get up into picking among such arms, it is mostly a matter of taste.