From: Patent Tactics, George Brock-Nannestad
Eric Jacobs has given a very full answer to the S- and straight arm question.
However, there is one further aspect of the tangential tracking arm question
and pivoted arm question that has to be kept in mind. The original
derivations of the advantages and disadvantages of the various pivoted arm
geometries was based on mono only, and coarse-groove dimensions. Percy Wilson
pointed out a special form of time distortion: the overhang in his elaborated
example meant a gradually slower reproduction because in effect the needle
tip moved along the groove during play. However, he calculated that on one
revolution at 78rpm the delay only amounted to 1/400,000 second. That is not
discernible to a listener. However, in the stereo case, and in particular
with line contact or elliptical stylii, the situation is different, and the
time scale between the two channels shifts. With a slower speed and higher
recorded frequencies there are definite time delay shifts between channels at
the high frequencies.
A tangential tracking arm will only alleviate the later problem if the line
contact or elliptical stylus moves in a true radius from edge to centre, and
if the edges of the stylus lie on that radius. A tangential arm is also
pivoted, but a mechanism ensures that its angular variation is held within
small tolerances; this is obtained by moving the carriage the pivot is
A different problem that is related to the problem of offset arms when used
for scratching is that when the stylus is pulled, it tries to straighten the
link from stylus tip to pivot. This link consists of three parts: the
cantilever carrying the stylus, the elastomer or thin wire bearing for the
cantilever in the cartridge and the tonearm. The straightening causes the
cantilever to assume a "zero" position that is at an angle within the
cartridge. Cartridges have individual sensitivities to having a "bias" in the
centre position; some magnetic cartridges will cause distortion, because they
"bottom" earlier in one channel than the other.
However, almost all cartridge-tonearm combinations, irrespective of pivoted
or tangential, have the same "straightening" problem in the vertical plane.
In order to alleviate this, the pivot for the vertical movement of the
tonearm ought to be placed where a line through the cantilever extended
backwards hits a vertical line from the pivot. And this has to be the case
when the stylus pressure is the intended one. The only tangential tracking
arm that has a chance of getting this relationship correct is the Revox. I
have never checked whether this is the case in practice.
Eric Jacobs wrote:
> Confusion over linear-tracking and pivoted arms aside, I wanted to add
> to the pivoted straight-arm versus pivoted curved-arm discussion.
> From a tracking distortion point of view (Baerwald & Loefgren distortion
> curves and nulls, etc.), the pivoted straight- and curved-arms are
> identical. If the connection between the pivot point and the cartridge
> is rigid, its shape (straight or curved) has no bearing on the tracking
> distortion. It's all simply a matter of geometry, and specifically
> the position and orientation of the cartridge relative to the pivot
> point. The shape of the rigid arm between the cartridge and the pivot
> point really doesn't matter when it comes to tracking distortion.
> However, from a structural dynamics point of view, the pivoted straight-
> and curved-arms are different. Structural dynamics is the study of
> structural stresses, strains and modes of displacement (aka resonances).
> See http://en.wikipedia.org/wiki/Structural_dynamics and skip down to
> "Modal Analysis" to learn more about structural dynamics.
> A pivoted straight-arm has very simple modes (aka resonances), with a
> single fundamental mode, weak even harmonics, and yet weaker odd
> A pivoted curved-arm has far more complex modes because of its shape,
> with multiple modes and a wider range of even and odd harmonics when
> compared to a pivoted straight-arm.
> Many would argue - including myself - that a pivoted straight-arm sounds
> better than a pivoted curved-arm (all else being equal, such as the pivot
> type and bearings, mass, etc.) because of the more complex modes and
> harmonics associated with its shape. Of course, things can be done to
> minimize these resonances by adding resonance damping material to any
> Aside from aesthetics, in particular the iconic look from the 1970s
> when the LP dominated and "S-shaped" or curved arms were popular,
> there are no sonic benefits to the pivoted curved-arm design over
> the pivoted straight-arm design (all else being equal, of course).
> There may be ergonomic benefits for some applications, although I
> haven't found that to be the case personally. I don't believe there
> are any pivoted curved-arm designs in present-day high-end audio.
> Eric Jacobs
> The Audio Archive, Inc.
> tel: 408.221.2128
> fax: 408.549.9867
> mailto:[log in to unmask]
> Disc and Tape Audio Transfer Services and Preservation Consulting
> On 12/17/11 1:18 PM, "Graeme Jaye" <[log in to unmask]> wrote:
> >On 17/12/2011 Andrew Hamilton wrote;
> >AH> I think Mr. Jaye meant to say "tangential tracking arms." However,
> >AH> tangential trackers do move along the radius of the disc. (: Better
> >AH> maybe to call the straight and S-shaped arms, pivoting.
> >Sorry to have confused anyone.
> >In my original post, I actually referred to "a radial tracking system"
> >- which means, of course, a linear tone arm (and tracks along the
> >radius of the disc, as you rightly say) - not a radial tone arm.
> >The main thrust of my comment was that Goran Finnberg had actually
> >confused the original question (which concerned the differences
> >between straight and curved radial tracking arms) with linear trackers
> >and went to great lengths to prove that he was right (which he was)
> >although not understanding the question.
> >Graeme Jaye
> >[log in to unmask]
> >Audio Restoration and Location Sound Recording