|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
124.168.143.135
In Reply to: Why? (nt) posted by mosin on April 15, 2007 at 19:03:48:
John is right, the skating force is proportional to the stylus friction which follows the Coulomb / Amonton law; it is proportional to the downforce and independent of velocity.If the vinyl liquefied at the interface the friction would become viscous loss which is velocity dependent and it would need to be increased for 45.
Follow Ups:
Skating force is proportional to friction and also proportional to distance between the friction point (stylus) and center of the rotating disk.
Regardless of speed of rotation, frequency of recorded signal, alignment, composition and viscosity of plastic, etc. skating force diminishes toward record’s end. Many tonearms’ antiskate increases towards record’s end. In that case lowering and readjusting antiskate for 7” 45s may produce marginal improvement of sound.
Marek
> Skating force is proportional to friction and also proportional to distance
> between the friction point (stylus) and center of the rotating disk.Skating force is proportional to friction, but it is not proportional to the distance between the stylus and the center of the disk. On the other hand, skating force changes slightly as the tonearm traverses the record as a result of the changing angle between the groove tangent at the stylus and a line from the tonearm pivot to the stylus. Therefore, the following equation will describe skating force for an unmodulated groove.
Skating Force = sin(θ)•VTF•µ
Where:
θ = The angle between the groove tangent at the stylus and a line from the tonearm pivot to the stylus
VTF = Vertical Tracking Force
µ = Coefficient of Friction
For a tonearm aligned to Baerwald's 66-121-mm null-point geometry, both θ and skating force will be maximum at the outermost groove. As the tonearm moves inward, θ decreases and so does skating force. The minimum skating force occurs in-between the null-point after which both θ and skating force begin increasing again all the way to innermost groove.
To put this into perspective for a 9-inch tonearm, skating force decreases by nearly 11% to its minimum value in-between the null-points. Then it begins increasing again to the innermost groove where it is still 4% lower than its original value at the outermost groove.
.
> Skating force is proportional to friction and also proportional to distance
> between the friction point (stylus) and center of the rotating disk.Skating force is proportional to friction, but it is not proportional to the distance between the stylus and the center of the disk. On the other hand, skating force changes slightly as the tonearm traverses the record as a result of
---
However, there are several experiments showing that skating force also increases across the whole disc, not because of velocity as such, but because of the more packed modulations compensating for the decreased groove speed. They can apparently increase friction for some reason, at least they did in those tests. I would think that more research is warranted, with a variety of modern styli and with various tracking forces.
Not an argument for using more anti-skating force with 45 rpm records, though.
If it's a single, it could be made of inferior vinyl with greater friction and thus greater skating force.
> However, there are several experiments showing that skating force also increases across
> the whole disc, not because of velocity as such, but because of the more packed modulations
> compensating for the decreased groove speed. They can apparently increase friction for
> some reason, at least they did in those tests. I would think that more research is warranted,
> with a variety of modern styli and with various tracking forces.I agree that more research is warranted. There is an excellent opportunity to implement this research. If Soundsmith or any strain-gauge customer would come forth with test results, that would basically resolve the antiskating question once and for all.
On the supposition that "shorter" modulations increase modulation drag, the 45, with its higher groove speed and therefore longer modulations, would require less skating force than a 33 encoded with the same signal.
Yes, on that supposition (and with the vinyl formula constant). More recent measurements would certainly be interesting to see.If I'm not mistaken, the difference in groove speed between a 33 1/3 record and a 45 rpm record at the same distance from the spindle is a good bit smaller than the difference in groove speed between the typical outermost and innermost playing surface of an LP.
What we need is one of those old skating-force cartridges with the gauge on the front. Better yet, I'll bet Soundsmith has some excellent data from their new strain-gauge cartridge, which measures skating force as it plays. ;-)Do you have any influence with Soundsmith. I think I probably pissed them off in December when I inquired about a DL-103R retip and pinned them down on SRA for their ruby cantilever, line-contact stylus assembly. Apparently they were simply replacing the stylus/cantilever assemblies on Denon cartridge without taking into consideration that the Denon cartridges were designed for 15-degree VTA whereas their stylus/cantilever assemblies were fixed for 20-degree VTA resulting in a serious SRA misalignment. Anyway, I'll bet they have all the data you can imagine on antiskating from their strain-gauge cartridge project.
Thanks. You put it in such a way that I actually understand it. :)
This post is made possible by the generous support of people like you and our sponsors: