STP distance. Is it critical ?

I think this is how it works....

Consider the arc of the stylus as it swings across the record surface. The proper set-up establishes two null points where the cantilever is on exact tangent to the groove, the inner and outer grooves have a small out-of-tangent angle.

Moving the pivot point of the same arm away from the platter center changes the position of the arc across the record surface. The two null points are moved closer together and the tracking angle at the inner and outer grooves is greater. Sound quality suffers at the outer grooves, but the tracking between the two null points is a little better.

Moving the pivot point of the same arm close to the platter spindle moves the null points farther apart resulting in a greater tracking angle error across the middle of the record, but coming closer to tangent on the inner and outer grooves.

In both cases of "improper" set-up, the worst-case tracking error is greater than if the arm/cart is set-up as designed. The differences in cartridge alignment points is based on the location of null points, and the location and degree of tracking errors.

Hi, Bpoletti: good description, and I appreciate that you put 'improper' in quotes. But worst case tracking error is relative. It's a matter of choice as to where along the path of the stylus that the listener hears the faint trace of distortion. The debate on which alignment null points are "optimal" will continue as long as people use pivoted tone arms.

Tom

Dear Bpolleti: You can make any " move/movement " you want with a pivot tonearm and always will have worst results that if you respect the different geometry set up equations where what you can change are the most outer/inner groove distances, the tonearm effective length must be the same.

If you move the pivot to spindle distance at random you have almost " nothing " but higher distortions..

A pivot tonearm always was and is designed with a precise effective lenght in mind/target not pivot to spindle distance, at least I don't know any pivot tonearm designer that his main tonearm target was the pivot to TT spindle distance but I can be wrong.

regards and enjoy the music,
raul.

Dear Raul, This is a kind of student-teacher situation; me
being the student asking the teacher if he is not'forgeting something'. We assume that all designers start with pivot-spindle (exact)distance. For the eff. lenght however they must assume éxact position of the stylus. As J. Carr stated there is no standard position or norm for the stylus. That is why those 'slots' in the headshell are needed. To compensate the (lack) of the standard.Ie to get the stylus where the designer ímagined its position.

Regards,

Dear Nandric: I already email you an example of equations used to find out tonearm design geometry parameters where you can see/read that the input/variables for those equations are these " numbers ": effective length and inner-most and outer-most values.

The STP distance comes by: effective length minus overhang.

IMHO a tonearm designer define first if he want a 9" or 10" or 12" effective length tonearm ( he does not cares about where the stylus in the cartridge comes, it does not matters: the cartridge designers has almost no standards about. Every one is almost different where the stylus comes in the cartridge. ) and not the STP figure that is only a result after knowing the other parameters through the equations, in specific the overhang.
At least this is the way how we start our self tonearm design.

Maybe there are other tonearm designers that goes through STP parameter but I doubt. Like I posted maybe I can be wrong but this is MHO.

Regards and enjoy the music,
raul.