Idler drive advantage is considered to be in the area of maintenance of inertial mass and motion under peak deceleration due to high levels of instantaneous deceleration.
Or, to not lose the microstabilty stability of inertial motion in those microsecond level deceleration drags from the stylus’s lateral deflections.It’s one of the reasons we like record clamps. Where the micro drag in transient peaks in the rotating plane is reduced.
this is important but not really looked at when most people talk about turntables. We knew about it back in the early 90’s at least (when I first looked at it, or found mention, anyway...), when we heard about how this particular form of motional stability ’slip’ could, on some turntables...would actually amount to a measurable partial rotation (total of number of rotations) in the playing of a highly modulated record side.
Since we ear via those transient peaks, almost exclusively and don’t actually hear the rest of the signal, then this small area of micro drag in this LP playback sytem, well, this becomes important. Core. The whole ball of wax.
One way to stabilize such a system in that area of analysis... is to utilize a high mass positive torque locked system with high inertial mass in the microsecond level of stabilization. thus a solid lock rim drive with a high spinning mass/high inertial mass motor connected to said rim drive.
Some transmission designs with complex gear sets with small idlers and the like are designed that way for for this exact sort of reason.To damp out micro deviations and to create continual positive lock across multiple conditions of draw. See videos of the massive NASA crawlers and their high speed spinning masses that help damp out micro deviations in motion and drive. The top of those Saturn V rocket was very far away and highly leveraged.. and the crawler must be incredibly stable across all four track sets... so they fell back on known mechanical solutions for achieving stability in the critical ways where such stability is required.
Re the design and build and execution of a turntable, one has to think if it as being
’first, you have to figure out where things actually have meaning or count, and then figure out what that means, how to measure it, and then circle such a thing back to the design and build’. It’s quite likely why these 100kg multiple platter gigantic S100k turntables are considered to be some of the best around (yes i know some are counter rotating).
Thus we can maybe see our way to considering that it really is about maintenance of a state of low micro-cogging of the speed accuracy, in the microsecond-to-microsecond considerations area. It’s why we see turntables with outer platter rim belts and three motors. And so on.
Essentially, if one was to measure the speed of a platter, at lets say, a rate of a million samples a second, with the measuring system being able to actually delineate such an attempt, with low distortion,..and commit such measuring with a low mass platter and weak motor..that the resulting deviation from microsecond considered speed accuracy (and maintenance), would probably look exactly like the transients that are printed into the record.
Where that measurement wiggle or trace.. would represent the dynamic accuracy lost. With dynamic accuracy being critical to the human hearing system, so it would be heard.
Which leads you right back to rim drive, and how it is done in these older designs.
I’m not saying that this is all correct thinking ....but it generally fits all the data at hand. That this set of points in analysis fits all the data at hand (anecdotal and in measurement, theory, etc) in a positive way, and also leaves paths for proofing it.
And to spoil the moment, a bit, yes all that sort of thinking went into our inexpensive (for what it is capable of) MM cart we are selling. All that was considered -and much more. Dynamically, it very much delineates micro and macro.
(I had mentioned all of this above re the idler drive...in a spur of the moment analysis, at an audio show (circa approx 2010) to Art Dudley, when he had just gotten into Idler drive turntables...and he was musing on the why and what he heard in them...as an explanation of the possible reasons behind the 'why' of what people felt they heard in such rim drive turntables.)
