Belt Drives in General have Two Bearings.
One utilised to Mount and Rotate the Platter, and one to supply a Lateral Force for a Coupling (Belt ) to rotate the Platter at a required Speed.
Two Spindles in use that can't be set into their housings, that are not making a tight fit, as this will create a friction, which will be a unwanted impediment to the desired function of the Spindles.
Two Spindles with a looseness that can create their own eccentric rotation, when rotating independent from each other.
Two Spindles that when coupled to each via a ancillary such as a (Belt), the presence of the Belt when coupled and supplying the necessary rotations. will pass to and throw the energies of the Two Spindles 'out of sync' eccentric rotations.
As a result of the two 'out of sync' eccentric rotations, Oscillation is now occurring and inconsistent tension of the Coupling (Belt) is occurring. The inconsistent Tensioning is now producing Speed Fluctuation and the Oscillations are also passing unwanted energy into the Platter.
Energies passed into the Platter are now at risk of contaminating the signal being detected in the modulation as the result of the styli tracking the groove, (a styli is not prejudiced, it will send a signal whether intended to be sent or not. The recordings design is not a protection, the Styli will send a signal born from a contamination from a unwanted source, where energies that are becoming a contamination are failing to be transferred away from the styli whilst in operation).
A method used as a control measure is to produce a Substantial Platter of High Mass, a 12Kg+ Platter might be considered a lightweight for some designs.
Put a 9Kg Platter onto a Inverted Bearing with a questionable Anchoring at the Base to the Structure and a Spinning Plate Design is in the making, excessive eccentric rotation of the Platter is only a period of short usage away, the impact of this on the Oscillation of the Belt and Speed Stability is one to run to cover from, but some are loyal to their product and bear with it, maybe investing in extremely expensive Speed Correction devices.
The wear that has been seen within the Bearing Housing of such a design is the worst samples when witnessed, bushes are almost ellipse shaped when the Inner Shape is observed, Heavy Platters on questionable Bearing Assemblies are not to be the best selected.
Some try to avoid issues with the inconsistent dimensions of the Belt causing Wow and Flutter, by adopting a Gossamer Thin type coupling material.
Add to the above the inconsistencies to be found in the Belt Dimensions and the Cogging of the Motor (Torque Variations), the Wow and Flutter is very much a concern and very sophisticated Speed Control Measures are becoming the next stage of investigation, some of which are more expensive that a very speed accurate of the Shelve TT and in some cases with a Tonearm and Cart' to boot as well.
Another method used as a measure to Control the Transfer of Energies that are a contamination and unwanted to be received by the Styli is to use a Two Part Support Structure.
A Design that adopts the Sub Chassis to reduce the need to manage external energies and Motor Transferred Energies. Where there are permutations as part of the design to mount the Motor, Platter Bearing and Tonearm on different Surfaces belonging to the structure, as a Measure to reduce the impact of Contamination born from the TT's usage and set up environment, especially where there is a desire to remove energy that is unwanted being transferred to the Platter/Styli.
There are also seen measures where the Motor is a Standalone Motor Pod, with the intention of isolating the energy produced from the motors operation, being transferred through the Support Structure the other Critical Parts to be mounted.
There has been a recent reveal within this thread, that there is a real concern for convection occurring, and this is a issue to be concerned about when a Standalone Pod is utilised. A convection occurring can certainly impact on the Wow and Flutter, especially if convection is to impact on the Motors positioning to the TT.
The Inconsistency of the Belt Tensioning will be the cause of Speed Fluctuations occurring as the result. Another issue some might find is best themselves if avoided.
A Suspended Structure is another Measure adopted as a design to manage Transferral of energies and a unwanted contamination impacting on the Styli.
In some cases a Sub Chassis is suspended from a Plinth. In such a case the Platter Spindle may be found attached to the Sub Chassis, in some cases the Tonearm is attached to the Sub Chassis as well.
Where the Platter Spindle and Tonearm are attached to the suspended Sub Chassis, there are designs using this method that have the Motor attached to the Plinth as a means to isolate energies created from the motor and reduce energy Transferral.
The Motor when mounted on the Plinth, is to supply a lateral force to a Platter that is attached to a Floating Structure. The energies produced from this lateral force is not only impacted on by the eccentric rotation of the Two Spindles and the Inconsistences of the Belt Dimension, the eccentric rotation of the two spindles and oscillation that is developing has the energy contained to create a movement of the suspended chassis.
The result being a increase to the Wow and Flutter as the Coupling (Belt) is now operating in a environment that has even more ambient impacts on the Belt, where much increased risk of Belt Slippage is able to occur.
Add to this a Sub Chassis that is able to produce a momentum when being influenced by a lateral load, when using a Platter of substantial weight, the Pendulum can get a momentum that will have the best capacity of most systems to increase Belt Oscillation that has an unprecedented impaction on the overall replay, each individual set up environment and support structure will yield very different end results.
There are quite a few items to be considered when considering the Belt Drive TT, from the most basic design to the designs that have gone to extreme lengths to engineer out a unwanted effect only to create New effect needing to be overcome.
Idler Drives and Direct Drives have lesser concerns overall, and they have developed their own fanbase for these reasons.
The Belt Drives have there following of hypochondriac worriers or those that are oblivious to the shortcomings of the design, and revel in its usage when nowhere near optimised.
All said an done I will one day have a decent session in front of a Kuzma Design, as I am liking their take on a TT, especially the Bearing Structure.
The report is that Hideaki Nishikawa is a fan too, good enough for him, certainly good enough for my limited knowledge on TT matters.
