Hi folks,
I am trying to determine how tiny the undulations are on a vinyl record groove - is it 0.1mm or 0.01mm??? Can’t seem to find this anywhere and just wondering for somethiing I am writing…
Grateful for any technical information…
JonathanG
Gramophone styli and groove geometries
The cutting tool on the disc lathe yields a v-shaped groove which is 56μm or 2.2 thousandths of an inch (0.0022") at the top and with the groove walls at right-angles to one another. Consecutive spirals of the groove are separated by an area known as land . The land dimension for 200 grooves per inch (g.p.i.) translates to a groove separation of 125μm (0.005"). The maximum grooves per inch rarely exceeds this figure.
The groove is drawn to scale in the illustrations below. (Note that the illustrations are tilted over by 45° to make the geometry easier to understand.)
The depth of the groove is nominally 28μm (0.0011"). The bottom of the groove is not, in fact, a sharp corner but has a radius of 6μm or 0.25 thou’ (0.00025").
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Start from “into the groove” section here;
Quote
This information can be stored in an area as small as a micron (one-thousandth of a millimetre), which also explains the sensitivity of record players to external vibrations.
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As with these things, be carefull and consistent with units of measure.Be they meter ,millimeter or thousandth of inches.
Unusually thou’ ( imperial) makes more sence in this application I’d suggest.
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Thanks guys - brilliant stuff!!!
Very grateful,
JonathanG
Just as addendum if you assume the average diamond stylus is 1mm long and scale that up to the height of the average human body - say 170cm some remarkable statistics emerge:
The average 33rpm record side has an average groove length of approx 500m
Scaled to human size that’s 0.5Km x 1700 = 850Km
Given it traverses that distance in around 22 minutes it must be travelling 850km in 22 mins
That’s 1440 mph - quite a ride that stylus tip has!!
JonathanG
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I like you said “average” since the linear velocity decreases from the outer to inner groove. Anyone know the average temperatures and pressures that occur at the vinyl/stylus interface?
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Responding to the thread title, for an unmodulated groove 28um both deep and half width, as suggested above, the absolute maximum physically possible extent of undulation upward/toward the groove centre (45 degree angle) would be 20um, at which point it would be level with the disk surface. The maximum in practice would be less. Peak to peak would be double, so 40um. That would be the absolute loudest possible sound with the above groove dimension - practical probably less, though I have in mind groove dimension is not a fixed thing, but for order of magnitude this will do.
With claimed practical 60dB theoretical dynamic range = 1 million amplitude range, the smallest undulation peak to peak due to the quietest reproducible sound will be one millionth = 0.00004um, or 0.00000004mm. The actual smallest undulation may be even smaller than because the practical maximum surely would be not right up to the vinyl surface, but I think this is probably a reasonable estimate of order of magnitude. This is assuming no dynamic compression/expansion in the RIAA pre-emphasis processing, which I think is correct(?)
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Quite amazing what a stylus tracking a groove can react to, and produce a correspondingly minuscule electric current arising from the tiny changes in a magnetic field caused by that stylus moving a magnet or miniature coul of wire.
But the ear is even more amazing!
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Always absolutely impressed with the engineering of the stylus/groove interaction and the care needed in mastering that groove. I recall that volume on the left and right channel are separate to left and right of the groove (in stereo) and also vertical movement. That and then the shape of the stylus tracking the groove at different heights in the groove relative to stylus shape is getting towards an art rather than an engineering solution.
I’m sure that many years ago Linn did the scaling thing, taking the effective length of a tonearm to the distance from Earth to the moon.
I’ve tried searching, but cannot find any reference.
It was in a LP12 brochure circa 1984, I have it somewhere in storage with all my Hi-Fi related materials.
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As well, I’m amazed how hearty and durable the vinyl surface is. I became aware of this property when I began cleaning vinyl using an RCM. Scrub that surface in two directions (repeatedly, if necessary) with a rigid bristle brush and ethanol solution. Vacuum dry with a velvet suction arm, wash again, and the surface noise is noticeably reduced. Amazing. For LPs unaffected by mildew, their longevity can exceed that of post-millennium produced CDs that fail to play. Simply put, the average LP produced in 1960 can still provide more reliable replay than a cheap, failing, thin CD produced in 2005. Not only that, many CD laser mechs are no longer available for replacement while there exists a vibrant market of new carts available for tonearms.
There is wear in playing a record - if a diamond stylus can wear, the very very much softer vinyl that causes it to wear must itself wear at a hugely faster rate, though of course that is spread over the entire length of all the grooves played over the same period. Every play will cause wear, how much depending in part on stylus shape and tracking weight, and long till evident will depend fundamentally on number of plays. It is possible that wear might be accentuated if any abrasive dust is present when played. In the case of a 50+ year old record that has only been played 50 times with a decent stylus etc might be imperceptible. But a record that has been played, say, 500+ times? Some of my favourite records will have well exceeded that, and whilst I certainly don’t rule out some or even much of the surface noise having bern due to ingrained dust from decades of play with only simple cleaning (no machine), I suspect that wear was also significant. CDs might not last forever, however for longevity music files on hard disks/SSDs with backups can last forever…
Leaving wear aside, it would be interesting to do the stylus to human scale size and weight contact force calculation, akin to the distance/speed comparison…
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