looking at upgrading my tonearm from a triplanar

- What is the significance of the hardness of a tonearm's bearings? At the tonearm weights involved, that alone wouldn't seem to be important.

The hardness is important- the more the bearing has the less sticktion. The size is also important- the smaller the bearing the less sticktion. Jeweled bearings (which are very hard) are unfortunately also very easy to damage and often don't survive adjustment at the factory, which is why they are usually adjusted with a little slop. If you over-tighten them they are damaged instantly. So a hard metal bearing is essential for longevity in the field. It is the failure of arm bearings that is why the arm may need to be readjusted over time.

- On the other hand, beside the bearing design itself, two bearing characteristics would seem, at least conceptually, to matter a great deal:

1- The bearing's ability to transfer mechanical energy out of the arm tube and into the mass of the turntable
2- The smoothness of the surface of the bearing material, for lowest friction.

The bearing ideally should not have to transfer any mechanical energy. If it does, this means that the arm and cartridge are mismatched (effective mass is incorrect). What the bearing should be doing is allowing the arm tube to move with the position of the stylus but otherwise simply keeping the cartridge in proper locus so that the stylus' set of angles with respect to the groove of the LP is maintained. The bearings IOW serve no damping properties whatsoever: this would run counter to their mission.

The bearing ideally should not have to transfer any mechanical energy. If it does, this means that the arm and cartridge are mismatched (effective mass is incorrect).

Strongly disagree. The effective mass/compliance relationship tells us only how a cartridge/arm behave when considered as a spring-loaded system. It tells us nothing about how they respond to internal vibrations.

No cartridge is 100% efficient as a transducer. All cartridges respond to cantilever movements by:
1) converting some of this mechanical energy to electrical signal;
2) converting some of this mechanical energy to heat; and
3) not converting some of this mechanical energy at all, which remains in its original state as physical vibrations.

The mix of 1, 2 and 3 is unique to each cartridge and varies according to frequency across the entire audible band (and beyond). The portion that remains as mechanical vibration may propagate through the cartridge body, into the headshell, into the tonearm and beyond.

Depending on frequency and phase, some of these vibrations will be reflected by material boundary layers, potentially setting up internal resonances. (This is very audible with certain cartridges, like those ZYX models with a blue ball on the front.)

Other vibrations may be dissipated as heat as they travel through various materials in the cartridge body, headshell or tonearm. (Well engineered wood tonearm wands are especially good at this.)

Still other vibrations may travel the length of the arm and reach the bearings. At this point, Bpd24's question comes into effect... how will the bearings respond to this?

Some bearings (Schroeder, Well Tempered) are designed to absorb/dissipate such energies. They do so to a greater or lesser degree, but inevitably suffer some loss in precision and dynamics. Other bearings (Triplanar, SME, other fixed bearings) may pass some energies into the arm base, while reflecting others.

No single bearing parameter (including hardness) is sufficient to predict the behavior of this highly complex process, which occurs across a nearly infinite number of frequencies. In particular, the compliance/effective mass relationship has no relevance in this area.

Hello Doug, I'm simply stating the theory. The bearing should have nothing to do with vibration from the cartridge.

If the arm tube is properly damped and the effective mass is given proper attention it will be found that this is the case.

You can make a similar argument for the suspension and steering in an automobile. If properly designed, the driver can get feedback from the road but it will not be tiring and won't bruise your hands or break your arm if you hit a bump. A damaged or worn suspension and steering system will result in handling problems, not unlike the inability of a damaged arm to properly track a cartridge.

The Triplanar has a damped arm tube and so its bearings (the hardest metal bearings made anywhere in the world) don't have a lot of work to do in this regard, but if they did they are also the best suited to the task.

Any way you look at it, its the best bearing system employed in a tone arm today. In order for anyone to do as well, they will have to get a security clearance. (Triplanar is grandfathered in, but they did get investigated by the Department of Homeland Security on account of the fact that they were using more of these bearings than Boeing Aerospace and the DHS wanted to know why. Turns out some DHS agents like Pink Floyd.)

Geoffrey Owens, the designer of the Helius arms, states that how an arm handles the mechanical energy created by the cartridge is his number one priority in designing an arm! Further, that the bearing assembly should optimally transfer that energy out of both sides of the horizontal bearings at the same time. If it doesn't (and I assume he will tell you very few do), there will be a faint echo created by the arm, because of the mechanical phase differential between the two. Wow.

Helius arms are offered with either Tungsten or Ruby bearings. Goeffrey acknowledges the potential for damage to the Rubies, but feels their surface smoothness is sufficiently superior to ANY metal as to make the risk a worthwhile trade-off. Viewed under a high-powered microscope (Geoffrey's other profession has been in Laser Optics), even the highest spec metal bearings have a very irregular surface. That, of course, creates sticktion.

As in everything else in Hi-Fi, tonearm design is a matter of conflicting design elements, requiring a choice on the part of both designer and consumer.

Viewed under a high-powered microscope (Geoffrey's other profession has been in Laser Optics), even the highest spec metal bearings have a very irregular surface. That, of course, creates sticktion.

The hardest metal bearings are not commercially available- you need a security clearance to get them and even then to get them you have to buy about $50,000 worth at a time (that is what Triplanar does). So this statement doesn't sound right. Did he state how it was that he was able to obtain said bearings? Or is he simply not measuring the 'highest spec metal bearings' as he states?