Analog Corner

At the 2013 High End Show, in Munich, a tonearm designer displayed a pivoting tangential tracker. A nearly invisible length of monofilament wrapped around the arm's perimeter controlled the pivoting headshell of the box-girder–like arm.

It may very well have worked as promised, but was it practical? And with so many tiny moving parts, would it sound any good? I don't know—it was a silent display—and inquisitive attendees kept bumping the difficult-to-see monofilament, dislodging it from its track.

The odds weren't good that this contraption, however well intended, would ever get past the prototype stage, though I was going to look for it at the 2014 Munich show, in May. Sometimes, designers obsessed with one particular performance parameter lose sight of the forest for the trees.

The designer of ViV Lab's Rigid Float tonearm, Koichiro Akimoto, also had in mind an unusual design goal, based on his belief that the geometry of pivoted tonearms, as we know it, is wrong.

What we know, or think we know, of that geometry all goes back to work begun in 1924 by Percy Wilson, technical editor of The Gramophone. You can read in detail about Wilson's work in Keith Howard's "Arc Angles: Optimizing Tonearm Geometry," in the March 2010 Stereophile. Basically, when a lacquer is cut, the cutter head describes a radius—a straight line—across the lacquer's surface. But most tonearms swing on a pivot: as the stylus traces the groove, it describes an arc across the record surface (fig.1).

In theory, at least, a linear- or tangential- or straight-line–tracking tonearm allows the stylus of the phono cartridge to maintain optimal tangency with both groove walls by reproducing, as closely as possible, the motion of the cutter-head's stylus across the lacquer. Because it does not maintain this optimal tangency, a pivoted tonearm produces lateral tracking error (LTE). But as Keith Howard points out, because a record's groove is a spiral, absolute tangency is never possible—but for our purposes, we can assume that it is.

Wilson's great contribution to modern tonearm design was his realization that to minimize LTE, the radius of the arc described by the playback stylus had to exceed the distance between the tonearm pivot and the platter spindle. The difference between those two distances is called the overhang: literally, how far past the spindle the stylus is when it is placed directly over the spindle. The overhang plus the pivot-to-spindle distance is called the arm's effective length. If your tonearm permits such motion, place it directly over the spindle and note the amount of overhang.

Wilson also calculated that minimizing LTE required that the stylus be set at an angle to the pivot point. This offset angle can be achieved either by bending the tonearm in an S shape or by angling the headshell. When this is done, two positions along the arc described by the stylus as it traces the groove, called the null points, produce perfect groove tangency, and LTE and the distortion it causes are minimized throughout the arc (fig.2).

However, Wilson's actual geometric calculations were incorrect: he didn't take into account that the groove's linear velocity is constantly slowing, from outer groove to inner groove. Eric Löfgren was the first to recognize and correct for the fact that LTE distortion is inversely proportional to linear groove speed, which, on a 12" LP, varies by a factor of 2.5 from outermost to innermost groove; in other words, in the same amount of time, the stylus travels 2.5 times as far in one revolution of the outermost groove as it does in one revolution of the innermost groove.

But that's [ahem] tangential to what this story is really about: Koichiro Akimoto's obsession with skating and antiskating, for which Percy Wilson is to blame. It was Wilson who devised the offset angle, and it is the offset angle that produces the vector force that causes a tonearm to "skate" toward the center of the record. Skating is not caused by centrifugal or centripetal force as the groove spiral shrinks (although you'll still find that explanation throughout the Internet).

In theory, absent the offset angle, there would be little or no skating. But play a record, and there's friction between the stylus and the groove—how much friction will depend on how heavily modulated the groove, the vinyl formulation (some vinyls are stickier than others), where on the record surface the stylus is, the vertical tracking force (VTF), and, of course, the stylus profile. A pivoted tonearm's inherent LTE itself also produces some friction, though very little.

Were there no offset angle, the drag produced by this friction would be in line with the arm pivot, which would be directly behind and in line with the stylus's cantilever, so the drag would be straight back. But when you add the offset angle, that imaginary line goes through the position of an imaginary pivot—the actual pivot remains over in left field.

Because of that distance between the imaginary and the actual pivot points, there is a vector force that causes the arm to skate toward the center of the record. The longer the tonearm, the less the offset angle, and the less the offset angle, the lower the skating force—but even a 12" tonearm produces measurable skating.

If you don't compensate for this sideways force, the stylus will ride the inside wall of the groove across the record. If you overcompensate, the stylus will ride the groove's outside wall. If your compensation is precisely accurate, the stylus will sit centered in the groove, where it belongs—but how likely are you to get it precisely accurate? Not all that likely across the entire side, though more likely with tonearms whose antiskating devices precisely vary the side-force compensation across the record surface. In short, antiskating compensation, like most attempts to play LPs perfectly, isn't.

As best I could decipher Viv Lab's poorly translated documentation, Akimoto also believes that the skating force does more than bias the stylus toward the groove's inner wall. He believes that it also displaces the cantilever the stylus is attached to, and exerts a force that de-centers the position of the coil or magnet inside the cartridge.

He also believes—and this is key to his work—that the skating produced by the offset angle results in more objectionable distortion than that caused by LTE. The gist of his calculations is that, at either the minimum or maximum LTE positions along the arc, uncompensated-for skating produces a condition in which almost half of the frictional force in the groove pushes the stylus against the sidewall.

Akimoto's point is that, even though it will have higher LTE, a tonearm with a non-offset headshell will produce only a tiny amount of side-force, hence distortion—and so, he concludes, a non-offset arm is preferable, all things considered. Once he'd concluded that an unangled arm was the way to go, he had to invent his own geometry, which resulted in cartridge underhang. The stylus of a cartridge mounted in the Rigid Float arm describes an arc that never extends past the spindle—in fact, at the beginning and end of its travel, it falls well short of the spindle.

Akimoto claims that his arm has zero tracking error at the arc's apex, which he's set to be in the center of the groove area, slightly closer to the label—probably to partly compensate for the greater inner-groove distortion inherent in vinyl playback.

So he built three . . .
There are three models of ViV Lab's Rigid Float tonearm: the 7, 9, and 13, respectively "about" 7", 10", and 13" long (footnote 2). Because there's no offset or overhang, length isn't critical, which begs the question: Why three lengths? Simply to more easily accommodate a wide variety of turntables. I got a sample of the Rigid Float 9 ($4500 at the time of writing; footnote 1).

As its name hints, the Rigid Float's geometry isn't its only unique aspect. 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!

The arm is housed in a heavy, truncated-conical base of brass; on its flat bottom are small, hard button feet. The arm is simply placed in position, not screwed or bolted down in the usual way.

If you have an unusually tall platter or prefer a spiked interface, you can attach three small, threaded feet. You can also adjust the cartridge's vertical tracking angle (VTA) and stylus rake angle (SRA) by loosening a large, knurled grub screw and raising the pivot housing by up to ¾" (18mm).

It's not the most convenient way to adjust VTA, or the most rigid—and if you (wrongly) feel the need to adjust a tonearm's height for every thickness of record, the Rigid Float will not be for you. But I found that when I set the SRA to 92° and left it there, the Rigid Float's system, though somewhat cumbersome, was workable. (When you've chosen a starting height, it's best to mark the pivot tower with a Sharpie so you can use that height as a reference and return to it as needed.) Azimuth is easily adjusted by loosening a grub screw on the arm's underside and rotating the arm tube.

Nelson Hold headshell and Setting Underhang
The Rigid Float 9 is fitted with an old-school, collet-type, bayonet headshell mount that's not the last word in rigidity—and, of course, it adds a break in the signal wiring. ViV Lab includes a Nelson Hold headshell, internally wired with silk-insulated wire of 99.99%-pure silver. The name derives from wrestling's full nelson hold, in which you clasp your hands behind your opponent's neck and press his or her head forward.

The headshell has a thin, almost tubular mount to which you affix a small aluminum crosspiece, to which the cartridge is secured with the standard mounting holes, nuts, and bolts. The crosspiece attaches to the headshell via a large knurled screw. The tighter you make that screw, the greater the pressure exerted on the cartridge body, and thus the greater rigidity of the mount. Caution: Irrational exuberance with this screw can deform a cartridge's body, particularly those made of hard plastic.

Since you position the Rigid Float's base on the plinth after you've installed the cartridge in the arm, underhang positioning is not a consideration. Still, to make the Rigid Float more compatible with a variety of turntables, the headshell has three closely spaced, threaded holes in which to anchor the cross piece.

The Nelson Hold's finger lift is an inline extension of the headshell that, unusually, is at the same height above the record surface as the rest of the arm. Unless you have skinny fingers and a deft touch, this makes use of the cueing mechanism mandatory.

Mechanical Ground or Mechanical Isolation?
One of the Rigid Float 9's claimed benefits is its mechanical isolation. Because the arm floats in oil, it's mechanically isolated from the turntable as well as from ground-borne vibrations. Energy generated at the interface of groove and stylus will be dissipated in the oil, not fed back to the interface. The same theory is implemented in the Well Tempered Arm, which floats a golf-ball-sized bearing in a pool of silicone.

Another way to remove energy from the system is to ground it, as in Allen Perkins's Immedia RPM 2 tonearm, which I wrote about in my review of VPI's Classic Direct turntable in the May and June issues: A post containing the bearing cup bolts directly to the armboard. The bearing point rests in this cup, making a direct mechanical connection between arm and armboard, so that energy from the groove/stylus interface has a direct path to mechanical ground. Of course, this means that energy also has a clear path to travel the other way, up into the arm—but that's easily handled with an isolation stand.

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Footnote 1: ViV Laboratory Ltd., 5-10-16 Imaizumidai Kamakura Kanagawa 247-0053 Japan. Email: Info@vivaudiolab.com Tel: +81 467-67-4495. Web: www.vivaudiolab.com. USA importer: Highend-Electronics, Inc., Apple Valley, CA 92307 (2014); Sierra Sound, PO Box 510, Wilton, CA 95693 (2025). Email: info@sierrasound.net Web: sierrasound.net.

Footnote 2: Michael Trei reviewed a more recent version of the ViV Rigid Float 9" tonearm in October 2024.—Ed.