Unipivot tone arms

There are various ways to implement unipivot tonearms, so, at best, one can only offer generalizations about how they perform.  A unipivot, by apply the whole force from the weight of the tonearm and cartridge on a tiny point, means that the bearing is very highly loaded and unlikely to rattle.  But even though it is highly loaded, friction is quite low because the contact area is small.  

From a practical point, most unipivot arms rock side to side when being handled, and that is disconcerting to some people.  Whether it rocks and otherwise behaves in an untoward way when playing is a highly debated issue.  Most unipivot arms employ some kind of damping fluid to damp undesirable vibration, but, even that practice has its detractors.

There are unipivot arms that go through quite a bit of trouble to reduce any tendency to rock sideways by employing stabilizing mechanisms.  Graham uses magnets on the arm that are attracted to magnets on a free moving structure that is on the base of the arm to stabilize the arm.  Basis unbalances the arm so that it has a tendency to want to roll in one direction, and that roll is then resisted by something that sticks out and contacts a roller bearing on the pillar of the arm.  Of course, these added structures do increase friction and thereby reduce one of the purported advantages of unipivots and such structures will, like any added mechanism on an arm, become a potential source of mechanical vibration.  Most unipivots rely on outrigger weights on both sides of the arm tube to add stability, sort of like the giant poles that tightrope walkers use for added balance.

As to sonic quality, one must judge that for oneself.  There are a few such arms that have a lot of fans.  Graham gets a lot of praise for their arms, as does Basis Audio.  Although not as commonly seen, Moerch makes arms that, to me, sound quite good with the right cartridge.

As I mentioned above, there are many kinds of unipivot tonearms, and different designs address performance challenges differently.  One cannot say that any particular design is superior or inferior because no arm does everything perfectly. 

Among the somewhat unique designs is the Supatrac tonearms that utilize both a fishing line and a sideways unipivot as the moving elements of the arm.  This is a unique design which I have heard, but, only in an unfamiliar system; the system did sound good to me.  

Viv Float utilizes a hardened ball sitting in a magnetic cup as a kind of unipivot.  Magnetic forces not only reduce the downward load of the ball on the cup, it is used to increase the resistance against movement of the bearing assembly within the cup thereby providing the needed rigidity of the bearing.  This arm has a lot of other unconventional design features that do away with most of the skating force on a cartridge at the expense of very high tracking angle error.  But, the end result is a very good sounding arm.  Again, it is hard to say how much the pivot design has to do with the sound, but, it sounds good so the pivot must be good.

The Kuzma 4-point arm is closer in design to a unipivot than conventional gimbal bearing arms.  It too is a very good tonearm.

I don't see any basis for saying that Graham, Basis, Kuzma, Supratrac, Viv Float, Moerch, VPI, arms are inherently inferior to other arms out there.  I don't think they are superior to other designs either.  There are many successful ways to skin this cat.

It might be cheaper/easier to build a unipivot, particularly because precision machining of the point and cup is not as critical as the machining of conventional gimbal bearings, but, some very good builders with very exacting machining make unipivot arms, and some very cheap arms are made with coventional bearings.  I don't think cost explains the choice made.  There are arms that do seem to be quite sloppy and chatter that are made with all sorts of designs. 

As to the Naim ARO, that is an interesting arm.  It may be a bit sloppy, and to my ears anyway "jangly" sounding, but I can see why some people like it for its lively character; I heard it perk up a system that sounded a bit too dark and dead sounding for my taste.

Effischer,

Thanks for your detailed description of your experience.  I heard a same table/cartridge comparison of a Graham arm and an SME arm.  There were subtle differences in sound, but nothing so major that one would even think it had to do with some major fundamental difference in design.  There are many good arms out there of all sorts of design.  I’ve owned gimbal arms, an air bearing tangential arm, a Well Tempered monofilament (fishing line) arm and two unipivot arms (Graham and Basis Vector); I currently use the Vector arm.  The easiest to set up and adjust is the Graham.  
There are many designs that purport to do a better job of addressing this or that performance issue.  But, any design, even if it is successful at addressing certain concerns (e.g. tangential arms to reduce tracking error), will not be strong in some other aspect (at least theoretically) and even then such weak areas might hardly matter with a good arm.  

The arm that seems to attack almost all theoretical issues is the Reed T-5 and it is quite elaborate and expensive.  I’ve heard it, but not in a system I knew very well.  Fortunately for my finances, it would not fit on my table.

You can achieve neutral balance with a unipivot, as you achieve it with other designs.  Graham arms, for example are neutral balance arms.  The Graham does not rely on the center of balance being below the pivot point to minimize wobble; that is done with magnetic stabilization.  There is no one inherent quality of unipivot arms that someone has identified here that cannot be addressed by correct design.  A good unipivot arm is a good arm, as is the case with all other designs.  

I helped with installing a Naim ARO on a Linn table.  The combination sounded good to me in the right system.  It was quite a lively sounding combination which sounded good in the somewhat dead system I hear it  playing.  Whether it would sound good in my more lively horn-based system is another matter.  Like any other component it matters how it works with other components and the sound one is trying to achieve.  But in the most gross terms for a tonearm/cartridge--whether it tracks properly, is not susceptible to troubles with warps, etc., the ARO performed well.

Daveyf,

To the extent that a unipivot might tilt when encountering some sort of irregularity in a groove, might this degree of freedom be a plus in that the stylus will tilt to accommodate the shape of the groove rather than plowing through the groove?  This is at least an interesting theoretical issue.  Thank you for raising it.

With almost ANY arm, I am surprised by comments about handling an arm.  I don’t see this as an issue at all.  I never cue by hand and my cue lever is never down except when I am playing the record.  There is no chance of any kind of error this way.

People often say they don't like how the arm tilts if they just stick their finger under the lift and trying to pinch the lift leads to them accidentally sliding the needle across the groove.  I say never touch the arm when you are ready to play the record; use the cuing mechanism.

I also hear people talk about accidentally bumping the arm while cleaniing the stylus or changing a record, or whatever, and having the srylus hit the platter.  Again, this never happens if, when play is done, one returns the arm to the rest and does not cue down.  It is just safer and more convenient to always be cued up until lowering the needle to play.