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     Turntable Skating and Anti Skating

 

Audiophiles are often faced with adjusting the anti-skating setting of their turntable to prevent an inward tendency of the stylus which could otherwise bias towards the inner record groove and cause uneven channel balance or distortion.

Other than referring to manufacturer’s recommendations, some audiophiles have attempted to exact this setting with something called an ‘anti-skate calibration record’ which is simply a blank record with no modulated grooves (only a smooth surface).  However, this will not succeed in determining anti-skating force because it is not the same as a grooved record, which renders a different set of mechanics.

The skating force the turntable stylus experiences when playing a vinyl LP is called a Centripetal force (centripetal meaning “center seeking”) because it is travelling around a curved path at constant speed.  Another force accompanies the Centripetal force called Centrifugal force (“outward fleeing”) which is equal and opposite to the Centripetal force.  Since the Centrifugal force is equal and opposite, one would think it should suffice as an anti skating force and keep the cartridge stylus balanced and centered in the groove.   However, although the Centrifugal force is equal and opposite to the Centripetal force, it acts thru the center-of-gravity of the entire tonearm - which if you recall - is located at the gimbal pivot.  This is where the tonearm balances.  When tracking force is added (such as 2 grams) this will move the CG slightly forward of the gimbal pivot, but it is still well out-of-position to provide substantial anti-skating force.

                   

        

 

The centripetal skating force is not considered constant over the entire playback of the record and varies according to mv²/r, where m is the mass of the tonearm, v  the tangential velocity of the record beneath the stylus, and r the radial distance from the spindle.  The anti skate control found on turntables attempts to account for this variation.       

For a grooved record, part of the outward anti-skating force (FAS1) is provided by the inner groove wall which is reacting on the inward centripetal force (or skating force Fs).  For a blank record with no grooves, this force will not exist and all the anti-skating force will need to be provided by the turntable's anti-skate control dial.  The two types of discs, grooved versus blank, are simply not identical and the dialed-in anti-skate force for a blank disc may approximately double what is actually required for a grooved disc.

Skating force Fs = Centripetal Force =  mv2/r  is counteracted by anti-skating forces FAS1 & FAS2 and to a lesser extent a possible component from the Centrifugal force situated near the gimbal pivot.  This questionable Centrifugal component is left out of the expression above for ease of illustration.  The component FAS2 is dialed-in by an anti-skate control located on the turntable.

 

Due to the possible false readings obtained from so-called anti-skate calibration records, it would be best to adhere the manufacturer’s recommendations for anti-skate settings, verified only by listening to a hi-fi test record.

 

              Anti-skate calibration record (Soon-to-be debunked ?)¹

 

1. Anti-skate systems of the future may change the outlook of antiskate calibration records.  At present, discretion is cautioned when using antiskate calibration records due to possible conflicting results with turntable manufacturers.