A Copernican View of the Turntable System

Dear Geoch – excellent post. You have provided me with three clear options that I understand and am thinking about.

“you can cover the entire underside surface (except the 2 holes) with a very fine velvet textile (extra thin without compliance) in order to damp the 2 metals that are coming in contact”.
This would be an easy solution and I can experiment with different velvet textiles.

“2 bolts may not be enough for the 3 coupling spikes option and can provide space for ringing or even worst a possible diformation of the Brass platform”.
Excellent observation.

I could add 2 more bolts to form a square around the 3 spikes? I can make the Brass plate smaller as well ? The ET tonearm post covers a very small area on the armboard.

“replacement of the upper coupling spikes under the Brass armboard by very tiny bearing balls (if you decide to try this option, by this way becomes easier. I'm anxious about the proper amount of tightness by the big bolts”

I really like this option - picking up some ball bearings is easy but just like torquing special wheels on cars - how do you know how much torque to use on the bearing. I guess I would start with a low torque and listen to familiar recordings – tightening a little at a time. When I used my TNT belt drive I would adjust the SDS by tone so I trust my ears for this.

“You have to choose by trial & error these 3 options unfortunately we cannot predict the results”

Everything we are doing in this thread is uncharted waters–for me that is the allure of it – the discovery – the learning first hand how resonances work in my vinyl setup. We only need to please ourselves. This makes the improvements very satisfying.

I have learned alot by your post.
thank u Chris

The SME type base of my Pluto 9A tonearm is covered with a very fine velvet textile, but has greater mass & height for it's small dimentions, is made of titanium that is bonded to a brass lower level & furthermore has 4 bolts that compressing the thin textile underneath and eliminate the possibility of compliance. To use only 2 big bolts its risky for this option as is also dangerous for the 3 bearing balls solution. There, you change the resonance freq by tightening the 2 big bolts, but they leave a free & lengthy surface that remains open & undamped to the mercy of any remaining vibration.

I'm sceptical about all this 'isolation' of the armpod that is being discussed?
Sound is transferred in only two ways:-
Structure-borne transmission
Air-borne transmission
In both these cases, we are interested in transmission in two directions......from armpod to tonearm and from tonearm to armpod.
With the tonearm mounting to the arm pod in the first instance, if there is any 'transmission' from the tonearm base, this indicates 'movement' in the tonearm base which is 'information lost' from the cartridge.
The aim of the tonearm is to have zero friction at the pivot point which means no transfer of any movement to the arm base. The arm itself must
be rigid enough to allow the cartridge to transfer all the stylus movement
to the tonearm wiring only.
In the other direction, the base upon which the armpod sits needs to be stable and immovable. The armpod needs to be 'decoupled' from this base (unless the base itself is acoustically decoupled and levelled) via spikes and the armpod must be absolutely level. With the mass of the armpod (at least in my situation) so large, any structure-borne transmission which somehow transmits across the spikes, is so small and high in frequency, that it is easily absorbed as 'heat' by the armpod.

With the air-borne transmission, please remember that the tonearm and the cartridge assembly themselves, are both directly affected by these same sound waves and are far more susceptible to vibrations (because of their more delicate masses) than the tonearm bases and armpods.
Again if one employs mass-loaded armpods, the amount of sound at varying frequencies which can be reflected and/or absorbed as heat is far more than that of any tonearm or cartridge.
If one wishes to employ a combination of dissimilar materials to counter the transmission of certain frequencies, I see no harm in that as long as visco-elastic ones which allow movement to occur, are avoided?

The above is simply my opinions based on the physics, acoustics and materials science with which I am familiar as well the 'in-field' experience of my Project. As usual YMMV? :-)

Dear Halcro, I can't see even one point in our texts that indicates any dispute. The armpod is by nature isolated once it is free standing & not attached to the TT chassis. Other than this isolation, not me, neither you we were willing to recommend any farther (ie: under the spikes' discs, or even in between the metal layers) as long as we can verify the ability of the shelf to drain the vibrations that intruding from air & floor, and also the effectiveness of the 6x1cm steel discs to drain the resonances coming from up through the spikes. But I feel that we must perceive the spikes as couplers. Theoriticaly we use to refering as decouplers all those viscoelastic materials that we want to avoid. I think as its going till now, this project is promising. Have you noticed any contradiction in the process so far ?

Dear Halcro, Thanks for the lecture reg. 'structure-and air born(sound) transmission'. This is done in the context of the arm pod formulation but, cause of the generality, must also apply to the TT's. We can see, so to speak, two
opposite approches: Raven, Brinkamann, Kuzma XL ,etc. on
one side and ,say, Thorens and Linn-LP12 on the other.
But the last mentioned use springs while the other don't.
Does and how 'mass matter' in this context? BTW this is a
kind of reformulation of my earlier question.

Regards,