Unipivot vs Linear Tracking

Great responses by all above. Of course it's important to note they're all talking about arms that cost far more than most pivoted arms (more than most complete vinyl rigs actually).

I haven't had the pleasure of working with a top level linear tracker, but I did own two of those Rabcos back in the day. Even those, crude as they were, were ridiculously easy to set up. Sonically they were at least the equal of similarly priced pivoting arms I had. Unlike everyone else on the planet, I never had a lick of trouble with either of them. I still have the ST-8 and it works fine.

My (pivoting) TriPlanar arm costs more than those Rabcos, the tables they were mounted on and all the cartridges I ever used with them put together. Is it better? Well, of course. In fact it's phenomenally better since, as noted above, any arm requires good execution and setup. But even with this marvelously adjustable device and plenty of experience, I can't dial in a strange cartridge in much less than 25 minutes, and a really good setup takes longer.

Linear trackers are based on the theory that tangency is the most important feature of the arm and that the linear tracking arm perfectly mimics the geometry of the cutting head of the master, whereas pivoted arms inherently display tracking distortion. However, the cutting head of the master is applying great force with a blade while a linear tracking tonearm is "dragging" the whole arm assembly across the record with a few grams of down force, quite a different situation. You could say that linear trackers are triumph of execution over practicality if they are done correctly.
I spent some time playing with one of John Elison's spreadsheets from vinyl asylum, plugging in values for tracking error for pivoted arms. I find it difficult to believe that a properly set up pivoted arm, even a 9 inch arm, has enough error to significantly "hear" the tracking error unless the arm is not set up correctly. I tend to think the audiophile imagination "knows" there is some tracking error and runs rampant to fill in the blanks to believe that 12 inch arm and linear trackers are audibly superior "because" of the geometry advantages. If somebody states they can "hear" the superior qualities of a linear tracker vs. a properly set up pivoted arm, I would be very skeptical.
I tend to believe that if linear trackers and 12 inchers sound better, it would be for reasons other than the geometry, either superior overall execution of the arm or better cartridge matching or higher effective mass etc. It is hard for me to believe that the "fumble factor" involved in a linear tracker would make it a better choice in every instance. The linear tracker seems to have many design disadvantages and pitfalls compared to a good pivoted arm. I hate to invoke the dreaded DBT, but that is one that I would like to see the results of.

I would have to concur with Cjfrbw, I've played around with the RS-3 rotary headshell vs a standard fixed headshell and from just casual listening, I cannot say that I can hear a difference in terms of tracking error distortion. But this is only from a casual 45min session when I first got the unit. I can say that I did not take any step backwards either. I hope to spend more time with it in the future. It is a new toy that has no instructions, so it will be trial and error to learn more about this rotary headshell.

Cjfrbw,

you make some very good points. why a particular product sounds the way it does is always complicated. how would one elimiate all differencs between any two designs other than a pivot and linear tracking. the answer is not likely to ever occur. so you could never get to a point where you have sufficently isolated the issues to use DBT to prove it. even then, i don't personally believe DBT proves better....at best proves differences were proved to a particular person under specific conditions at a particular moment.

so we are left to assign characterisitics based on experience.....imperfect as that might be.

my personal perceptions about linear tracking on my tt may be as much as result of the eddy current direct drive motor, and the air bearing on that motor and the 60 pound platter. it may be the vaccuum hold down, or the 250 pound plinth. it may simply be the quality of build, and not linear tracking.

my opinion is that when you do go to the trouble to do 100% of all the things that can be done to make a tt perform optimally; one of those things is linear tracking.

The linear tracking arm is without doubt a better setup than any pivoting arm, but the friction of the arm when it travels has to be reduced to near zero. Most linear tracking arms use an air bearing which is complex and delicate, and the air compressor is noisy.

There is, however, another approach which is used by my Sony PS X800 turntable. The arm is moved by a servo motor, just like the arm which carried the cutting head when the recording was made. The movement speed is biased to match nominal groove spacing, and then that speed is varied to match the actual groove spacing as measured by any angle of the arm. The arm is not fixed perpendicular to the track, but can pivot slightly: the servo moves the pivot point. The servo is well designed and does not exhibit any of the problems that some folk fear (hunting, oscillation, etc). Tracking error is maintained at less than 0.05 degree. Note that the servo approach is equivalent to a completely frictionless bearing. There is no sideforce on the stylus...not even the tiny force needed to move an arm with an air bearing.