|
Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ. |
|
|
|
Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ. |
|
In Reply to: Anti-Skating? another newbie question posted by Leo on December 7, 1999 at 13:58:57:
Friction between stylus tip and the groove wall produces a force tangent to the groove. This frictional force depends on tracking force Fv and the friction coefficient my [3].Ff = Fv x my
my varies with record material and amount of groove modulation.
The reaction force of the tone arm passes through the arm pivot.
These two forces combine as vectors and, due to the offset angle of the cartridge, leave an unbalanced force, the SKATING FORCE force. This force, being perpendicular to the groove tangent, tends to pull the arm towards the record's center.
Skating force is further determined by length of the arm, the magnitude of the offset angle, tracking force, shape and condition of the diamond (new, worn) and record material.Skating force, when uncompensated, produces distortions in the right channel (outer groove wall). Tracking force on the inner groove wall is increased, on the outer groove wall decreased. Uncompensated skating force results in increased record and tip wear at the inner groove wall.
Higher modulation velocities result in increased skating force [2].
Groove velocity appears not to change skating force. [2].
Groove radius has an effect on skating force in that there is a minimum at about 3.5 inch with maxima at outer an inner grooves, the value at outer groove being higher than at inner groove [2].
The skating force Fs is a function of R (groove radius), D (overhang) and L (effective arm length = linear distance arm pivot - tip point) [2, 3].Formula : Fs = Ff tan phi [2, 4]
Ff = Frictional force = Fv x my
Sin Phi = (a x b) ; a = R/2L ; b=1/2RL x 2LD-Dexp2phi (angle between groove tangent and tone arm axis,) varies across the record surface with a minimum at about 3.5 inch and maxima at inner and outer grooves, the outer maximum being higher than the inner, which fact coincides with the Fs plot of [2].
You need a groove to produce that skating force, so you need also a groove to adjust anti- skating. Try the Hifi-News and Reviews test record. There is a track for anti-skating adjustment (4 tracks at increasing signal levels).
Be aware that, if you use another protractor or tone arm setup procedure than the one provided with the tone arm or recommended by the arm manufacturer, respectively, the geometrical relations of arm-cartridge-record change, which result in a change in skating force and hence antiskating setting. The skating compensation provided on the arm is designed for the arm being adjusted according the manufacturer's specifications or using the manufacturer's alignment gauge (such as SME).
In this case it has to be set roughly equal to tracking force.From the above it can be seen that correct compensation is possible only in two points on the record (due to the parabolic shape of the curve). Skating force compensation is thus only a compromise. I set mine with the HFNRR record and forget it.
[1] Alexandrovitch : A stereo groove problem, JAES, 1961, Jan., p.166
[2] Kogen : The skating force phenomenon, Audio, Oct.1967, p.53 ; Nov. 1967, p.38
[3] Bauer : tracking angle in phonograph pickups, Electronics, March 1945, p.110
[4] Oakley : Skating force, mountain or molehill, Audio, March 1967, p.40
I found literature indicating that the reaction force goes through the arm pivot axis along the arm axis, not along the line connecting stylus tip and pivot axis. This different approach gives different formula and values for skating force. I'm busy finding out which version is correct.Thanks for having read the story so far.
Klaus
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Re: Skating force (the story so far) - Klaus 03:26:32 12/09/99 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]