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On 17/12/2011 14:31, Andrew Hamilton wrote:
> I think Mr. Jaye meant to say "tangential tracking arms."   However, the
> tangential trackers do move along the radius of the disc.  (:     Better
> maybe to call the straight and S-shaped arms, pivoting.
>
>
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> Andrew
>
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> On 12/17/11 9:12 AM, "Doug Pomeroy"<[log in to unmask]>  wrote:
>
>> It is my understanding that a radial tracking arm will
>> be tangent to the grooves at two points on the disc
>> surface, and that this is true of both straight and curved
>> arms.  Or have we overcome the laws of physics?
>>
>> Doug Pomeroy
>> POMEROY AUDIO
>> Audio Restoration&  Mastering Services
>> Transfers of metal parts, lacquers,
>> shellac and vinyl discs&  tapes.
>> 193 Baltic St
>> Brooklyn, NY 11201-6173
>> (718) 855-2650
>> [log in to unmask]
Would it help if I summarised?

There are, broadly, two ways in use of supporting a cartridge.

The more common one is to use an arm, generally of between nine and 
twelve inches in length, pivoted and counterweighted at one end and with 
the cartridge at the other. This will describe an arc across the record 
surface, which path differs from the radial path of the cutting head on 
nearly all extant discs. This path difference is referred to as 
"tracking error", and is large on an arm of finite length, unless the 
cartridge is offset by an angle and overhung with respect to the record 
centre by a distance obtained by the formulae of Percy Wilson and 
others. These factors are commomly optimised for minimum error at the 
minimum recorded diameter or for minimum error at two points over the 
recorded area, with the intention of making it as small as possible over 
the whole side. (The position of the cartridge and the offset angle are 
the parameters which matter here - whether this is achieved by an offset 
headshell or a single or double bend in the arm tube is decided by other 
factors.)

This is a well-tried method which worked well for decades, giving finite 
but small and manageable tracking error. Then came the DJ craze for 
"Scratching", that is manually moving the record back and forth under 
the pickup, often much more violently than would be done in broadcast 
back-cueing, for instance. This causes forces to be sent into the arm 
which the offset (from which also arises the need for bias correction) 
partly resolves into an outward thrust which causes the stylus to jump. 
This being uncool, some manufacturers (Stanton included) offer an arm 
without an offset, such that the forces produced by scratching act 
solely through the pivot axis and therefore have no outward component. 
The tracking error is, of course, hideous, but irrelevant in this 
application.

The less common way of supporting a cartridge is by some form of arm 
which causes the stylus to move along a straight line between the edge 
and centre of the disc, thus mimcking exactly the path of the cutter. 
Much in the way of an electrostatic loudspeaker, first experiments 
indicate this is the only way to go, but making a robust and reliable 
product using this principle is not as easy as it looks. Some, such as 
Revox, succeeded.  Others did not, or only did so at prohibitive cost.

In the case of the Stanton turntable, one would select the S shape arm 
for any application except DJ work.