Discuss The Viv Lab Rigid Arm

@dover 

I am suggesting keeping the headshell offset at 0 ( straight ) move the arm mounting point forward in order to set 2 null points.

The combo of properly set offset + overhang is the only way to get the 2 null points.  If you eliminate either one of those aspects you can only achieve a single null.  This single null still requires proper setup to achieve it.  

My gut feel is that the straight headshell has more impact than the "underhung" geometry.

I am starting to believe the effects skating force are painted with much too wide of a brush.   One only needs to set a traditional arm with no antiskate on a blank record and note the speed at which it flies to the center.  Now take an underhung arm without offset on the same record and in theory the skating  forces should identify the location of the single null.  This will not be immediate and will take several seconds.  The thing that is interesting about this is while both setups do have skating forces involved, the magnitudes of the two are vastly different.  One could argue that the application of 'proper' antiskate to an offset arm will result in forces similar to that of the underhung arm but then we have to consider how modulation level comes into play and the need for a big brush to cover up the reality hiding in the cracks becomes clear.

dave

Would love to get Peter Lederman @retipper (SoundSmith) take on this.

Dover, perhaps to add to what Intact wrote, or not, if you move the pivot forward so the tonearm is not underhung but becomes either overhung or even set to hit the center of the spindle (I guess we can call this "un-hung" or neutral hung), then you can have no null points at all (without headshell offset). Because at the null point, the tonearm from pivot to stylus tip can be thought of as one side of a right angle triangle, let’s call that side A. The distance from the stylus tip to the center of the spindle is then side B of a right angle triangle, and the distance from the pivot point to the center of the spindle is side C, or the hypotenuse of a right angle triangle. Pythagorean Theorem tells us that for a right angle triangle, C-squared = A-squared + B-squared. But in the overhang condition, side A is greater than side C. So tangency is impossible without headshell offset. The un-hung situation cannot work either, where A = C.

Dear @intactaudio : "" The combo of properly set offset + overhang is the only way to get the 2 null points. ""

Well, the standard alignments we all know including Stevenson B the null points are output parameters calculated from only 2 other knowed parameters that are:

most inner groove radius ( mm. ) and most outer groove radius ( mm. ). and from here came the standards: IEC, DIN or JIS.

Null points calculation it not depends of any other parameter, not even tonearm EL.

Again, that is for the knowed kind of alignments.

R.

@rauliruegas 

Null points calculation it not depends of any other parameter, not even tonearm EL.

Whaaaa???  

you need to specify at least four parameters which typically are alignment type, inner groove diameter, outer groove And Pivot to spindle (P2S).  The math then returns you  two null points, effective length (EL) and offset angle.  The overhang (OH) is then found by subtracting P2S from EL.  The knowns and unknowns can be reworked based on the information available.  Effective length can be substituted with a known overhang and the P2S returned.

dave