I guess someone calculated that based on their photos, a 1.0 mil spherical stylus in a 90 degree groove causes distortions IN the vinyl starting at .64 grams, and these softened ripples then come to the surface afterwards.
AES E-Library: The Limiting Tracking Weight of Gramophone Pickups for Negligible Groove Damage by Barlow, D. A.
The Limiting Tracking Weight of Gramophone Pickups for Negligible Groove Damage
JAES Volume 6 Issue 4 pp. 216-219; October 1958
It has been observed that when spherical styli are dragged over flat vinyl surfaces, scratches are produced under loads considerably exceeding the elastic limit as calculated from theory. The author, in this paper, describes the results of his experiments which bear out his argument that under load the point of yield begins below the surface; and reaches the surface, producing visible tracks, only after the calculated yield load is exceeded. This critical value of load for styli of various radii has been measured and found to be equivalent to, for a 1-mil stylus, 0.64 gm. for a 90° record groove. No size or skin effect was found with the vinyl material tested.
Author: Barlow, D. A.
Affiliation: Aluminium Laboratories, Ltd., Banbury, Oxon., England
Some of these photos are very interestinghttp://www.micrographia.com/projec/proj ... ny0200.htm
The Microscopy of Vinyl Recordings.
A General Introduction.
The Vinyl Record.
This article is in five parts:
Page 1. Page 2. Page 3. Page 4. Page 5.
Microscopy: The appearance of the grooves.
Contaminations causing noise; old forms of stylus.
Record wear and the elliptical stylus.
Stylus tracking and test records.
ANOTHER AES PAPER from 1978
AES E-Library: Groove Deformation and Distortion in Recordings by Barlow, D. A.; Garside, G. R.
Groove Deformation and Distortion in Recordings
JAES Volume 26 Issue 7/8 pp. 498-510; August 1978
The elastic and plastic deformation of vinyl record compound under indenters of various profiles has been studied in large-scale tests. Curves of total depth of penetration versus load have been used to calculate the net distortion on record playback. In general, in the lower treble, net distortion is less, and in the upper treble, net distortion is greater than tracing distortion alone. This is important for attempts to reduce tracing distortion by inverse predistortion of the recorded signal. Nylon was also studied as a material with contrasting mechanical properties to vinyl. Further light has been shed on the nature of translation loss.
Authors: Barlow, D. A.; Garside, G. R.
On the Steve Hoffman forum PUBLIUS says this
A few references on groove melting and deformation...
"Role of Scanning Electron Microscope in Disc Recording." George Alexandrovich. AES Preprint 1274, 58th Convention.
Among other subjects we investigated was the method of playing records wet. By applying a thin film of water as the record was rotating and playing the groove with an ordinary stylus, it produced unexpected increase in vinyl deterioration in the area where the stylus was touching the groove. Our SEM pictures unveiled extraordinary ripping of the vinyl surface which I can explain only by the fact that the vinyl is not allowed to liquify momentarily under the pressure of a fast moving stylus because of the cooling action of water in the groove. This phenomenon, I believe, is identical to ice skating where one does not skate on ice but actually on a film of water which comes from the ice being momentarily melted under the pressure of the thin metal blade. If ice is too cold, one cannot skate. Evidence of the fact that vinyl melts can be found in pictures taken of record grooves played at different temperatures.
KlausR linked (http://db.audioasylum.com/cgi/m.mpl?for ... l&n=441735
)to a section from "Handbook for Sound Engineers" on AA. Note that Alexandrovich is also responsible for this quote.
because of the small area of contact that exists between the stylus tip and the groove, the pressure against the groove wall can rise up to many thousands of pounds per square inch. For instance, if the wall receives 0.7 g of force applied through the contact area equal to 2 ten millionths of an inch, the pressure is 7726 lb/squ.inch. It has been experimentally shown that with such high pressures and forces of friction between stylus and the vinyl, that the outer skin layer of the record material melts as the tip slides over the plastic and then refreezes almost as fast as it melted. It has been suggested that since the melting temperature of vinyl is about 480 °F that the same temperature exists in the contact area. If the record material is metal, which happens when metal mothers are played, then the pressure increases to 20,000 to 30,000 lb/squ.inch, and the temperature can reach 2000°F because there is no plastic deformation of the groove wall. This explains why styli made of diamond, which is nothing more than carbon, literally burn up or wear out in a couple of hours when they are used to play metal mothers. If liquids were used to cool the contact area, then the diamond wear diminishes drastically, but the metal surface of the record is burnished. If the liquid is applied to the vinyl surface, then the temperature of the plastic surface cannot reach increase and melt; therefore, the scouring of the groove wall can be observed, as shown in Fig. 25-114.
There is some other anecdotal evidence I haven't been able to track down. Apparantly an old issue of The Audio Critic had a guy show examples of melting too. I haven't even tried looking through Audio yet.
On the other hand, Friedrich Loescher of Lenco was apparantly adamant (http://db.audioasylum.com/cgi/m.mpl?for ... g&session=
)that vinyl melting did not exist. It's worth noting that he was also a staunch supporter of wet playback, and had the electron microscope wear pictures (and the subjective evaluations) to prove it. (see "Long-Term Durability of Pickup Diamonds and Records", JAES v22 #10 p800 (Dec 1974).) In comparison, the first Alexandrovich article I linked above (the preprint) shows pictures of the vinyl being physically ripped apart when played back wet. So this could be an example of two experts with diametrically opposed opinions, except that Alexandrovich's opinion was used in at least one published book (the handbook), and his research was done several years after Loescher's...
Here's the CBS discussionhttp://www.bostonaudiosociety.org/pdf/b ... -7508b.pdf
Theory of Groove Deformation in Phonograph Records: Another from CBS, this one modern
theory and a comparison with experiment, emphasizing the interaction between stylus tip and
vinyl surface. (pp. 1332-1340)