What defines a good tonearm

my perspective is that the most significant percieved and discussed weakness of a unipivot is actually it's biggest advantage, which is the freedom to wiggle. it is the micro and nano wiggling following the groove unimpeded that gives it the advantage over a fixed/gimbaled bearing pivoted arm which on the micro and nano level cannot follow the groove as well.

A tone arm should not really follow the groove- it is the cartridge that must do that. The arm must keep the cartridge in locus. If you think about it, if the arm *really did* follow the grooves the cartridge could not make any sound! Thus we come to the idea of effective mass the the ever-important issue of mechanical resonance.

Unipivots however do not rule the roost by any means when it comes to freedom in the motion of the bearings. For example, the Triplanar arm employs an ultra-hard bearing that is so hard and so precise that Triplanar got investigated by the Department of Homeland Security because they were using more of these bearings than Boeing was. Triplanar maintains that a problem with all needle-and-cup bearings is that the bearings get damaged after only a small amount of use- whether gimbaled or unipivot design. That is why the bearings they use are so hard- 7 or 8 grades harder than the bearings in an SME 5.

The Triplanar has an adjustable azimuth system consisting of a worm gear that can tilt the arm tube. If you look at how a cutting lathe is built, its obvious that the azimuth of the cutterhead never changes- the cutter assembly rides on a extremely precise machined stainless set of tracks with stainless wheels. As far as I have seen, (and microscopic motion being the nature of LP reproduction) only a gimbaled arm can have the same kind of azimuth accuracy.

Thanks Ralph. So far, your explanation makes the most sense to me. Next time around, in my next life, I check out the Triplanar!

Best

Unipivots however do not rule the roost by any means when it comes to freedom in the motion of the bearings.

Besides air bearing, unipivot does have the least friction and freedom in motion. I don't care what fancy gimbal bearing you have you cannot beat a needle on a dimple. On top of that, the bearing is preloaded by mass so I don't see how you can have bearing chatter and not to mention adding a drop of oil or lubricant in the reservoir. The problem with unipivot is, obviously, not about lack of movement but TOO MANY planes of movement, namely in the azimuth or torsional motion. Micha Huber of Thales tonearm boasts about the quality of his Swiss made bearing but admits it's still not as low friction as a unipivot. So let's not bring Department of Homeland Security into this. Let's just deal with the real issue of a unipivot.

There are many ways to deal with the azimuth rocking of a unipivot. Traditionally, designers place the counterweight or outrigger/side weights below the pivot point. Much have been written about this so I won't repeat here. In recent years, designers started to use a secondary bearing to assist the main bearing and sometimes, completely eliminates azimuth rocking which also render it no longer a true unipivot and it might not SOUND like a unipivot but I don't own a Basis Vector, Continuum Cobra & Copperhead, so I can't tell. As a unipivot user myself, I can sympathize with Mike's sentiment about the its "freedom to wiggle" that creates its sonic character whether that's an advantage over gimbal bearing or not is something debatable.

my perspective is that the most significant percieved and discussed weakness of a unipivot is actually it's biggest advantage, which is the freedom to wiggle. it is the micro and nano wiggling following the groove unimpeded that gives it the advantage over a fixed/gimbaled bearing pivoted arm which on the micro and nano level cannot follow the groove as well.

Since Talea uses magnet to control azimuth rocking, as I am told, I would have to place it in the same genre with the Graham Phantom. It's an interesting development in tonearm design. The traditional mass below pivot point of stabilizing has a weakness in dynamic due to its pendulum affect and I am curious about the dynamic performance of arms like Talea or Phantom. Mike can report that to use.

As far as I have seen, (and microscopic motion being the nature of LP reproduction) only a gimbaled arm can have the same kind of azimuth accuracy.

Gimbal arm does not guarantee azimuth accuracy. The Triplanar's way azimuth adjustment is placed before the offset angle at the headshell, unless the worm gear is angled accordingly--approximately 23°--that adjustment will affect VTA. Bob Graham brilliantly uses two side weights angled 23° at the bearing housing to prevent that VTA change while changing azimuth. Same concept in the Vector, Cobra, and Copperhead. Smart.

Again, a quasi-unipivot tonearm like Cobra, Copperhead, Cobra and precious few others, that use a rigid secondary ball bearing does NOT exhibit any azimuth motion at all. So let's not lump all of them together.

At the end of the day, all tonearms have some sonic traits that please you and some others don't, just pick your cup of tea or poison.

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Thanks Hiho. So far, your explanation makes the most sense to me.

I used to bad mouth unipivots.

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