Because this is an unusual and controversial tonearm design, and has had astonishing claims made for its performance by the manufacturer, this in-depth report goes deeper and is longer than is usual for. We will return to a reasonable balance of reportage in the next issue.

The manufacturer's initial advertisement for their mis-named "Vestigal" arm (footnote 1) was so laced with nonsense that we will admit to having been skeptical about the product from the outset.

For example: Transcriptors claims that the "Perfect Arm" should have zero mass. If it did, the low-frequency resonance due to the compliance of even the best cartridges would occur in the upper-bass range, and the output would peak at that frequency and fall off rapidly below that. Transcriptors claims that the "Perfect arm" would work at zero tracking force, which is a nice idea to entertain but will just have to wait until some genius perfects a cartridge that works without contacting the groove. Transcriptors claims that phono "system resonance" should ideally occur above 30kHz, and then claims the resonance of their arm to be "over 180Hz."

They fail to point out that there are two fundamental resonances in every pickup system, one at the limit of high-frequency response (due to stylus mass vs vinyl compliance), and one at some low frequency (due to stylus compliance vs the combined effective mass of the arm and cartridge) below which the pickup's output falls off rapidly.

We will not comment on the other rather bloated claims that Transcriptors makes for their new arm, except to observe that the last time a disc system was "hopelessly outdated" was when the LP replaced the 78, and that some of those LPs that we own which have been played over 100 times are still what we would consider Hi-Fi, albeit rather noisier than when new.

So, what is this wondrous device anyway? In all respects but one it is a conventional (although certainly not conventional-looking) low-mass tonearm. The difference is that, instead of havinq its vertical pivots located back at the arm base, they are placed right behind the cartridge. It is a most unusual-looking arm, with a vaguely spidery quality that some people find oddly repulsive and others find fascinatingly attractive. Unlike the Stax and the SME arms, which look unambiguously like precision instruments with the flash of costly jewelry, the Transcriptors Vestigial gives the subtle impression of something alive, which is undoubtedly why it seems to elicit such a strong reaction from so many people.

You've probably seen the ads for it, but the photos of it are more tantalizing than enlightening, so in case you've never taken a close look at it "in the flesh," so to speak, our sketch below shows the details of its construction. The pivots about which lateral motion takes place are located to one side of the base of the arm, so the entire length of the arm is involved in lateral (horizontal) motions. Vertical movements, however, occur about a pair of pivots situated right behind and beneath the small platform that holds the cartridge. And that is what's so unusual about the Vestigial arm: Its inertia (mass) in the vertical plane is much lower than that of any other tonearm.

Low vertical mass is a good thing, up to a point at least, because it allows the cartridge ride up and down over record warps without significant change in tracking force. Thus, a cartridge that requires 0.5 grams of force for clean tracking with most discs can actually be tracked at somewhere near that figure, because the force won't drop much below its nominal setting when it rides the downhill portion of a warp.

It's an ingenious idea, but while the Vestigial design is unique in some specific respects (its odd-ball shape, for example), it is not the first tonearm to use this principle. Pickering & Company had an arm with its vertical pivots right behind the cartridge as long ago as 1953, and it was followed subsequently by similar designs from Shure Brothers (the "Studio Dynetic") and Gray Labs. All three had the distinction of coping more easily with warps than any other designs.

Actually, Transcriptors does not make any claims for their arm's ability to cope with warps. What they do claim for their design is a "180Hz system resonancewell outside air-moving frequencies no distortion or feedback." Apart from the gobbledegook quality of this description, it sounds like a recipe for disaster, for if "system resonance" did occur at 180Hz or thereabouts, the arm could be expected to skip grooves on heavy modulations near that frequency, and its ability to stay with the groove below that frequency would be dubious at best. Fortunately, that "180Hz system resonance" appears to be as illusory as some of the other sky-pie touted by Transcriptors.

Resonances

The arm has a rated effective moving mass of 1 gram vertically and 6 grams laterally, including the cartridge. The initial advertisement for the Vestigial arm shows it with an ADC XLM cartridge, which weighs 3.8 grams and has a rated compliance of 50x106cm/dyne.

The formula for calculating the low-frequency resonance of a tonearm-pickup combination is

where F R is the low-frequency resonance in Hz, M is the total effective mass of the arm and cartridge in grams, and C is the compliance of the cartridge in cm/dyne (footnote 2).

Calculating the resonances in each plane of motion yields a figure of 9.2Hz lateral and 22.5Hz vertical. These figures were confirmed (within 0.3Hz) by our measurements using slow sweep tones. (Several of the CBS test discs have sweeps extending down to 10Hz; the frequencies were halved by running the discs at 16 2/3 rpm, taking the lower limit down to 5Hz.) Neither of these figures even approaches the claimed 180Hz resonance.

In fact, in order to get a system resonance at 180Hz with a pickup of the XLM's compliance, the effective mass would have to be 0.016 grams. With a mass of 1 gram, on the other hand, the pickup compliance would have to be 0.78x106cm/dyne in order to achieve system resonance of 180Hz! We wonder, now, where in Heaven did Transcriptors get their 180Hz figure? And who would want it anyway?

Footnote 1: The dictionary does not acknowledge the existence of this word. It does however list "vestigial."

Footnote 2: Manufacturers' compliance figures are usually for static conditionsthat is, with the stylus displaced but stationary. The figure will usually be different under signal-modulation conditions, but the difference at low frequencies is not likely to be enough to affect significantly computations of arm/cartidge resonance.