Halcro, Lew,
A straight arm with no offset is normally set to one null point a little inside of the center of the recorded part of the record. I think this would correspond to 96 - 98mm from the spindle.
There is an arm like that now called Viv Rigid Float. It has won some accolades. I've never heard it. "They" say the benefit is from eliminating most torsional forces on the cantilever.
Regards,
http://stereotimes.com/post/viv-lab-rigid-tonearm |
Fleib, another such arm that preceded the Rigid Float is the RS Labs RS-A1. As you say, it uses "under-hang" and thus achieves tangency at one point on the LP surface. Both of these arms are in the realm of the crazy, but I can say that the RS-A1 really works and sounds way better than I would have guessed. Thus I am curious about the Rigid Float. What bothers me about it is the question of whether the pivot is really held "Rigid" by the floating bearing arrangement. I don't see how it could be. The instructions that come with the RS-A1 suggest 21 mm of underhang is optimal (stylus hits the LP 21mm short of reaching the spindle) but this is more a suggestion than a rule.
Halcro, I agree that a 20-inch arm with a straight head shell would have very little tracking error because of its sheer length, and the skating force would be weaker than in most cases. But the trade-off is the potential for lack of rigidity of an arm that long, plus high effective mass. Interesting for sure, nevertheless. |
Lew,
You mean 21mm short of the lead-out groove, which would be about 80mm from the spindle?
Reducing torsional affects on the cantilever is extremely important and obviously a tradeoff for alignment error. The Viv arm won a couple product of the year type awards so it might be very good?
I believe the pivot is held in place with some kind of magnetic fluid.
http://www.highend-electronics.com/viv-labs.html
Regards, |
08-28-14: Lewm:
"What bothers me about it is the question of whether the pivot is really held "Rigid" by the floating bearing arrangement. I don't see how it could be. " In the August 2014 issue of Stereophile, Michael Fremer reviewed the tonearm and wrote something about the bearing: "The arm lacks a conventional bearing. Instead, the pivot floats on a dark, magnetic, light-viscosity, ferrofluid-like oil that you inject into a large opening at the front of the pivot housing. Before you do, the arm is too stiff to pivot; afterward, it smoothly glides on what appears to be a bubble of oil without visible means of support. According to inventor Akimoto, inside the pivot, a small ball floats on a “slimy rubber swimming ring that regulates the arc motion of the wand.” There must be a cup-like structure inside that holds the oil, and a vertical rod—the pivot point—that is somehow steadied by but floats within the oil. I couldn’t pull the arm to and fro, and yet it floated freely. Very ingenious, however it works!" It sounds like the arm might be a modern remake of the Gray oil damped unipivot design using "magnetic fluid." But the distributor claims the following: (1) Absolutely no mechanical contact at arm pivot bearing mechanism, resulting in highest sensitivity and maximum amount of howling margin (Which promises to reproduce rich but much tight base sound with no distortion, no muddiness, the most clear sound and wider dynamic range).
(2) There are similar type of bearing pivot, dipped in oil bath (Oil damp Type), available in the market, but still they require some string or another apparatus to fix fulcrum for arm rotary motion but RF, thanks to automatic positioning mechanism, requires absolutely nothing to interfere with the force, for cartridge stylus to follow the inward path of record groove.
(3) There might arise some lateral mechanical instability of arm with this type of bearing, but RF, equipped with the most appropriate balancing mechanism, assures the stability of the focus. This is the reason to be put the name of ""Rigid Float"". So in the end, I don't know. . |
This tempts me to try my SAEC WE-8000/ST as a straight tonearm 😜⁉️ It comes with a ceramic off-set headshell but I use a whole lot of other headshells which I can use without twisting the cartridges as I currently do...😎 What do you guys think I should aim for as an underhang....bearing in mind the Viv Lab uses from 5mm to 20mm....👀❓ |
