Stylus Shape Information

So what is the big deal with stylus shapes?

I will try to cover some of this topic here.

The Conical Stylus

When long playing (LP) records were first invented, the only type of stylus was the conical / spherical type.

But there were issues...

The diameter of the stylus was too large for it to fit between the corrugations in the groove which recorded higher frequencies.
Reducing the diameter of the stylus was not possible as it would cause the contact patch to drop too far down the groove... and the tip of the needle might then drag along the bottom....

Solution: The invention of the eliptical stylus, simply put it has a small diameter at the sides and a large diameter front to back.

The Eliptical Stylus

The smaller the diameter of the side radius, the better the stylus can track/follow the high frequencies - suddenly sibilants no longer distort!



Standard eliptical sizes are:
0.4 x 0.7 mil / 10 x 18 um - budget styli
0.3 x 0.7 mil / 8 x 18 um   - quality styli
0.2 x 0.7 mil / 5 x 18 um  - premium styli



Line Contact & Shibata Styli

All simple so far right?

Well.... not quite.

When they developed CD4 Quad 4 channel recordings, they needed to be able to record and play back frequencies up to 45kHz - more than twice the highest goal frequency attained with the eliptical styli.

Also the very fine corrugations in the groove required for 45kHz could be more easily worn away, so a design was required that could 1) track much higher frequencies and 2) Reduce wear on the record.

The first stylus that achieved this was the now famous "Shibata" (named after its inventor).
(Edit: The earlier Pyramid stylus - released in the late 1950's appears to be the first attempt at a Line contact stylus, however at that time there was no pressing need for it in the market, and the concept appears to have failed commercially, and disappeared with very little trace. - The idea was then resurrected with the release of CD4 and the Shibata.)

Eliptical and Shibata Stylus showing contact patch

Proportions of the Shibata design
6 x 75 um - Shibata "large" design
6 x 50 um - Shibata "small" design

Rather than providing a small cicular "dot" contact point with the groove, the more complex shape of the Shibata allowed a long vertical line of contact to be achieved with the groove wall.
The result of contacting more of the groove wall was the achievement of the two primary goals.
Through better wall contact tracking was improved and information retrieval improved (facilitating higher frequencies), and because the total contact surface area increased, the amount of pressure per square area was substantially reduced - less pressure equals less wear on both the record and the stylus.




In actual fact the side radius of the Shibata is about the same as a 0.2 mil eliptical - so theoretically they have the same ability to trace high frequencies, but the eliptical only ever contacts the same small area - which can become worn - resulting in degradation in high frequencies.
Playing back a record with a Shibata stylus which has been worn with a conical or eliptical stylus can result in near pristine sound - this is because the Shibata shape can "read" the groove wall in areas that were not contacted by the simpler stylus shapes.

After the release of the Shibata, various competitors developed very similar shapes which were (and are) marketed under various names:
Hyper Eliptical (various sizes!)
Stereohedron 0.3 x 2.8 mil / 7 x 72 um
Line Contact  (various sizes)
Fine Line         8 x 40 um
These are all much the same.

Exotic Styli

The next development was driven by a designer called Van Den Hull in Holland - using computer analysis he developed a stylus shape which replicated the head of the cutter used to make the original vinyl masters as closely as possible, while reducing the side radius further.

This meant two things: 1) the reduction in side radius reduced distortion and improved tracking of the high frequencies, and 2) the increase in the length of the contact patch further reduced wear and increased longevity of stylus and record.
This led to the next wave of stylus shapes, again known by various names:
Micro Line     2.5 x 75 um
Micro Ridge  3.8 x 75 um
VanDenHull   4 x 70 um
FritzGeiger    5 x 70 um
SAS               2.5 x 75 um
Paratrace       4 x 70 um

Although the proportions of the individual designs vary a little - the side radius in most of these is around two thirds to half that of a Shibata - so effectively 0.1mil.

These "Exotic" styli are usually made by computer guided laser cutting of diamonds to a precise pattern - and the price also reflects the additional effort required to manufacture these.

Wear, Tear and Life

So we know that the more extreme line contacts reduce wear.... but what is the difference?

Apparently according to Jico (manufacturer of the highly regarded SAS stylus), the amount of playing time where a stylus will maintain its specified level of distortion at 15kHz is as follows:

Spherical / Conical     - 150hrs
Eliptical                        - 250hrs
Shibata/Line contact  - 400hrs
SAS/MicrRidge          - 500hrs

This is not to say that at 500 hrs a SAS stylis is "worn out" - but at that stage the wear has reached the point where distortion at 15kHz surpasses the level specified by Jico for a new stylus. (Which I believe is 3%).

Some manufacturers have traditionally defined a stylus as being "worn out" when it starts to damage the record... in these terms the figures provided by Jico can at least be doubled, and in some cases quadrupled.

SUMMARY

In pure sonic terms on pristine vinyl a top notch eliptical can do as well as all but the very best Line Contact / Shibata styli, but will ultimately be surpassed by the better MicroLine styli.

However in terms of reduced wear on both stylus and records - the entry point is the Line contact / Shibata category.

In terms of playing back worn vinyl line contact stylus types also have an advantage in that they can contact "virgin" unworn vinyl.

Narrower side radius = improved tracking and reduced high frequency distortion.
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