If you were to design a tone arm, what would it look like and feature?

^^^^^
Larryi - very interesting design that Reed T-5 linear tracker. Always liked the Reed products never owned.

https://competition.adesignaward.com/design.php?ID=68105

From their website.

Tonearm’s turning part is based on low noise thrust-sleeve bearing. For angular rotation limited rotation sectional torque motor is designed and built.

OPERATION / FLOW / INTERACTION:
Tonearm’s position is controlled by laser and linear sensor grid. When tonearm is operating, laser beam should point into a center of linear sensor array. LED indicator shows tonearm status.

This part with the motor and laser sensor grid sounds complicated to me; and who knows how reliable its going to be. I prefer air bearing linear trackers which are by themselves passive devices, their levitation comes from an external air pump, the movement solely by the groove friction. External pumps are easily exchanged at will.

Also just a note.
The cart lateral strain reference you mention in your post is not a general one but based on comparison to specific linear trackers. I can tell you that the one I use, the ET 2.5, has been measured to have half the lateral strain of my pivot arm due to its unique counterweight design. This allows the owner to use the highest compliance MM if they choose.

Cheers

ct05171,

All air bearings rely on very low friction of the main bearing to allow the cartridge to easily pull the arm along.  To some extent, conventional arms also pull the arm axially to a new position, but, they employ the mechanical advantage of a pivot, something the linear tracking arms cannot do.  At least theoretically, this means more strain than a pivoting arm.  I never encountered the problem myself, nor any friends using air bearings (friend had the same ET arm as you have), so this might just be a theoretical issue.  Any sensor approach, such as that of the Reed, that then employs a motor to make an adjustment has the theoretical problem of having to catch up with a wrong angle, with some possible overshoot, mechanical noise from operation, etc.  A similar approach to that of the Reed (moving arm base) is used by one version of a Shroeder arm, but the base is moved by the arm being pulled into the right position by friction (a different compromise).  

I like the sound of the air bearing arms I've heard.  They tend to have really good bass response--full and powerful without being muddy.  I suspect that comes from the high lateral mass resisting the lateral movement of the cantilever when tracking monophonic bass signals (that means that all of the groove displacement is translated into bass signal instead of some being lost by the cartridge moving side-to-side). 

I like the Reed arms. They meet all of my requirements. The T5 is a bit over the edge. It is very complicated for minimal return if any. But, I have not seen or listened to one so I really have to reserve comment. In the world of mechanical devices simplest is usually best. 

The Reed arm is fundamentally, a simple, captured bearing design arm.  The only complication is the moving base that maintains cantilever/stylus tangency to the groove and eliminates skating forces.  Optical sensors have been around a long time (e.g., Beogram 6000 from the 1970's) for controlling servo motors to maintain tangency.  I don't think this makes the Reed arm unduly complicated, but, it is a matter of debate whether its advantages are worth the trouble.  The big issue, to me, is the price and possible problem with fitting such a massive arm on a particular table.

An arm from the past that is interesting to me is the Air Tangent arm.  There is one very rare model that allowed for setting VTA by remote control while the arm is playing the record.  That would be the only practical way to set VTA on a record-by-record basis.  That might be fun, although I am still to lazy to do that level of fiddling around.

I have not heard some of the ultra-exotic arms that go to extraordinary measures to damp and control vibration such as the SAT arm or the Vector Superarm 9.  These are too expensive for my consideration, but, I would like to hear them anyway.

Back in the early 80s I had a Rabco I modified. I used carbon fiber for the arm wand, and set up a more sophisticated servo system, using a capacitance in parallel with the motor.


This caused the arm servo to not quite stop and also not speed up like crazy- it would track the LP and establish a speed that kept the arm more tangential. I never got around the bearing issues of the arm and track.


But some years back I found a zero-slop slide on which the arm mechanism (designed for motion control/robotics) could be mounted.

So if price were no object I would use that slide/block system with a servo similar to what I used before: probably light activated rather than using metal whisker contacts. To this I would add something that was similar to a Triplanar in that everything could be adjusted and equipped with the hardest metal bearings available (which is what the Triplanar already uses).