How important is low W & F performance anyway?

@dover The torque curve is shaped like a sine wave with minimum torque at 0° and maximum torque at 90°.  With no load on the motor, the rotor and magnetic fields are aligned (0° lag);  as the load increases, the rotor will start to lag the magnetic field as it delivers torque to the load, creating an electronic torsional "spring".  If the rotor falls behind the field by more than 90°, the torque produced actually decreases as the load further increases, the "spring" breaks and the motor will stall.  At low torque levels the angle is small and the relationship is nearly linear on the slope so small changes in drag will produce an almost linear drop in speed.  You are correct that pushing the static load up the curve will eventually reach a point where small dynamic loads will produce smaller changes but for that to be really effective means you are operating close to the stall torque which I doubt is the case.  But in theory, you are correct in your understanding.  That at least is my understanding, but feel free to correct me if I'm wrong.

There is also torque ripple to consider. Pushing the motor harder usually increases this parameter as it is generally a percentage of the average torque developed. These perturbulations would be fed into the platter. Aligning all these disparate motor characteristics for best performance is a complex balancing act and there is no perfect solution     

My understanding is that on sustained piano notes 0.2% Wow & Flutter is marginally audible, and 0.1% is typically inaudible. So if reviewers are not commenting on levels much higher than this they are either not listening to the right material or not listening carefully enough.

@lewm 

I think the earliest version of the 301 did use a grease lubricated bearing which then became the eddy current brake that RB describes

My Garrard 301 is the grease bearing type, and has the eddy current brake.  I am pretty sure the eddy current brake was there on every Garrard 301 and 401.

If Garrard had chosen a synchronous motor, the actual speed of the platter would depend predominantly on the diameter of the pulley on the motor shaft.  Actually, this pulley is stepped with separate diameters for 33, 45 and 78. Getting all three diameters exactly right for every deck would have been impossible, back in those days, in my opinion.

Aftermarket suppliers like the Classic Turntable Company offer replacement pulleys in multiple size increments, and recommend getting a pulley which positions the braking knob on the lighter side.  Different pulleys are needed for 50-Hz and 60-Hz operation.

These units were designed to run 24 x 7 in broadcasting studios.  The BBC would have been fastidious about speed stability, back in the day when they had a dozen self-directed audio engineers, whose speaker designs are still influential today.

@phoenixengr 

The W&F numbers for both tables are typical of belt/idler drive, but speed accuracy is more problematic.  The Holbo has a DC motor which has a negative torque/speed curve

Yes.  I posted here for several reasons.

One was to provide a data point (I cannot personally detect wow and flutter with my tables).  Maybe that's two data points.

With a plethora of standards and measures within those standards, just quoting a number is pretty meaningless unless you also quote the standard and the measure.  I was impressed with the way Garrard describe exactly what their measurements involved, and that they individually test every 301.

As I mentioned, the Holbo is pretty much a black box to me - two black boxes if you count the power / air supply box.  There is a four-wire cable from the power / air supply box which powers a DC Japanese motor (about 4-Watts) and transmits switching information, at the very least to tell the power supply when to switch on, and that the turntable has been switched off.

Garrard goes to great lengths to allow speed accuracy to be observed and corrected via a big front knob which adjusts its eddy inducing magnet.  The feedback loop is via the operator and big strobe markings cast into the rim, though.  In my experience it hardly ever needs adjusting.

Another reason behind my post was to suggest that wow and flutter can be measured and reported separately.  When these measures are combined, the same number could arise from low wow and high flutter, or high wow and low flutter.  There are unlikely to be equally annoying.

The various standards have differing filter curves, presumably to prevent rumble from affecting the flutter results, and long-term instability from affecting the wow results.  The separation of wow and flutter is at 4-Hz, as far as I know, and the curves are designed to reflect human sensitivity.  Most tests last only a second - you can't get a long-term speed stability measure in that timeframe.

At first glance, a wow and flutter measure seems to tell a casual observer the % range which a turntable's speed variation won't exceed.  Unfortunately there is much more to the standards than meets the ear