vet
Audio, Δημοσιογράφος
- Μηνύματα
- 8.252
- Reaction score
- 8.153
παντως αν θες να μαθεις για αυτο που σου εγραψε ο φιλος, ξεκινα διάβασμα...
Here's what literature has to say with respect to record wear:
1 mil = 1 thou = 25.4 microns (1/1000 inch)
===============================================
1. Barlow, Groove deformation in gramophone records, 1958
Limiting load for plastic deformation for a 1 mil tip in a 90 deg groove is
0.64 gr. A 0.5 mil tip presents a side contact area of 23.4 square microns (from Davies below).
2. Flom, The deformation of plastics with hard, spherical indenters, J. of Audio Eng. Soc. 1959, p.122
Plastic deformation on vinyl occurs for a 0.005 cm stylus at 5 grams static
load.
3. Walton, Gramophone record deformation, Wireless World 1961, July, p.353
Shows a graph with VTF vs stylus radius : plastic deformation is caused for spherical styli of 0.0003 inch at 2.1 gr deformation, 0.0004 inch 2.7 gr, 0.0005 inch 3.1 gr etc.
4. Anderson, Some aspects of wear and calibration of test records, J. of Audio Eng. Soc. 1961, p.111
Investigation concerning the wear occasioned by the initial playing of test
records at various needle forces.
Frequency response curves were taken to show high frequency wear. The first playing, especially at high VTF, accomplishes a large part of the wear observed after 20 plays. A first play at 9 grams had worn off 1.5 dB. For the same standard M3D cartridge at 9 gr a drop of 5 dB at 15 kHz occured, at 6 gr 2 dB, at 3 gr no drop , all drops indicated after 20 plays
Results : the first playing, especially at high tracking force, accomplishes
a large part of the wear observed after 20 plays.
Wear drops rapidly as tracking force is reduced. Measured was frequency
response; it turned out that the response dropped by up to 5 dB at 15 kHz, indicating high frequency wear.
5. Oakley, Inner groove distortion, Audio Magazine 1962, June, p.57
For 0.5 mil styli a VTF of more than 3 grams tends to erase high frequencies
6. Hunt, The rational design of phonograph pickups, J. of Audio Eng. Soc. 1962, p.274
One of the resonances present in the system is the stylus groove resonance which is difficult to suppress. It's maximum is especially in the
intermediate portions of the stylus suspension. The transducing mechanism is sensing motion in that portions so that the resonance will appear in the electrical output of te cartridge as spurious response.
Solutions are either to locate such resonance above the audible range or to apply damping.
Damping is ordinarily chosen. This damping, however, leads to overdamping at frequencies other than the resonance frequency. An additional force is thus exerted on the stylus in the
mid frequency range. The increased force leads to increased frictional work and to increased wear.
7. Walton, Stylus mass and reproduction distortion, Wireless World 1963, April p.171
Pictures of stereo grooves played with pickup at 2.7 gr VTF (stylus mass 3
mg). Permanent indent depth = half modulation depth. After 5 playings, little further deformation is visible. Low effective tip mass is advantageous.
8. Kogen, The elliptical stylus, Audio Magazine 1964, May, p.33
VTF for 0.2 mil 0.9 mil elliptical stylus should be no greater than 1.5
grams.
Frequency response :
0.2 mil elliptical tip
no change at 1 gr VTF
slight change between 10 20 kHz at 1.5 gr after 100 plays
significant change between 10- 20 kHz at 3 gr
0.7 mil circular tip
slight change between 10-20 Khz at 3 gr after 100 plays
More wear because of smaller contact area for the elliptical tip.
A record played at 1.5 gr with 0.2 mil elliptical tip showed signs of wear
under microscope, but this wear was not detectable in the sound.
9. Barlow, Groove deformation in gramophone records, Wireless World 1964, p.160
Presents a 1 thou radius stylus under increasing static load : not
calculated but observed at 12 mg, fully elastic range
at 0.5 gr, plastic deformation just reaching the surface
at 2.5 gr, fully plastic range
10. Bastiaans, Factors effecting the stylus/groove relationship in
phonograph playback systems, J. of Audio Eng. Soc. 1967, p.389
Yield point of record plastics = 14,500 psi. He refers to older papers
saying that in the stylus/groove contact, sub surface yielding begins near a load of 0.150 gr and plastic yielding at 1 1.6 gr (for a 17.8 mil tip). Microscopic examination of a groove played with 2 gr VTF revealed a slight permanent indentation track on both groove walls.
11. Anderson, Phonograph reproduction Audio Magazine 1978, May, p.3 (pt.1), June, p.42 (pt. 2)
Tracing distortion relates to size and geometry of the stylus tip.
Distortion decreases and wear increases with decreasing tracing radius of
the tip. Record wear is related to tracking force and trackability. Minimum
distortion results from a tip of 5 microns. This demands a VTF of lower than 1.5 grams. By well designed shape of the tip the tracing radius gets small without having a too small contact area. The contact area is related to indentation and stress in the groove wall, thus influencing wear.
Tests were carried out with the version IV cart with biradial, hyperbolic
and hyperelliptical (25.4 x 38 microns) tips. As far as record wear is
concerned, no difference between the tips was found, when playing with 1.25 grams.
They further state that at that time, there was no measured evidence that
the use of a long contact area stylus (van den Hul, fine line, micro line, microridge = 3.8 x 76 microns ) allowed to play with more than 1.5 grams without affecting record life.
12. Pramanik, Understanding phono cartridges, Audio Magazine 1979, March, p.33
Record wear in UNMODULATED grooves starts at about 3 gr. Wear is not only directly attributed to VTF, but also on friction between the tip and the groove wall.
A correctly shaped and well polished tip does not cause wear.
The compliance is determined by stiffness of the elastomer cantilever
suspension and the cantilever length. Elastomer stiffness is not constant, but varies with frequency. With increasing frequency compliance decreases (becomes stiffer).
The suspension exerts a force attempting to restore the stylus assembly to its mean position (the optimum position for what the stylus was designed for). The stiffer the suspension (the lower the compliance) , the larger is that force. VTF must be at least as large as the restoring force in order to maintaining contact with the record.
Starting from the mean (design) position:
1. when the stylus attempts to move below the mean position, the cantilever restoring force tries to move it upwards. Here VTF comes into play to avoid that the tip loses contact.
If VTF is too low or smaller than the restoring force, the stylus will loose
contact and cause severe damage when bouncing back into the groove.
2. when the stylus attempts to move above the mean position, the total force on the record is the sum of restoring force and VTF.
If compliance is low and, as a consequence, VTF is rather high to maintain
contact with the record for the largest amplitudes to be found (low frequency trackability), the sum of forces can be so large as to result in stylus pressure that deforms the groove into the plastic region, causing permanent damage.
As far as effective tip mass (ETM) is concerned, it plays a role in the high
frequency region, where acceleration is high. VTF must be at least as large as the force defined by ETM (F=m x a) and the largest acceleration on the record.
If VTF is too low, the stylus again will loose contact.
Even when VTF is adequate, the pressure on the tip when on the bottom of the groove is due to the sum of forces required to accelerate ETM and the VTF, which is constant. The larger ETM, the higher the forces and the higher the pressure exerted on the groove which may be sufficient to cause plastic deformation.
So one has an interest to have a cartridge with low ETM and rather high
compliance to avoid high VTF.
13.Davies, Close up look of record wear, Audio Magazine 1980, Sept., p.38
Scanning electron microscope study for Shure's M91ED cartridge with 1 gr VTF and a not specified MC with 2.5 VTF (records were played 50 times) on high quality audiophile record.
Even the unplayed record showed signs of surface imperfections, e.g. holes.
Shure : photos show audible loss of quality. Pieces of vinyl have come off
the surface. Distinct wear lines can be seen parallel to the groove. The
type of damage caused is termed surface conchoidal fracture, resembling
broken of shattered glass. The groove surface reminds glass surfaces being chipped by fine sand.
Another record shows enormous damage after 50 plays, showing the same type of damage and many longitudinal wear lines.
MC : tearing and gouging wear is predominant (dust as grinding agent).
All styli present pressures of 30.000 to 69.000 psi with a VTF of 1 gr.
These high pressures have led people to assume that plastic or permanent deformation occurs, the yield point of the vinyl being 14.500 psi. Static indentations in the elastic range can be described by the equation of Hertz.
It appears that no solution exists for the plastic range, especially for
sliding indentation with friction.
The study found that the quality of the vinyl plays an important role as far
as sound quality is concerned. In particular the filler material used is of great importance, it seems that it has tendency to split off. Dust in the groove is pushed and pounded into the groove wall, scouring and gouging the wall.
