A Copernican View of the Turntable System

The base as an island, I am not sure?

The fundamental objective of turn-table design is to maintain an optimal geometrical relationship between the stylus and the groove in such a matter to allow, as Halcro so eloquently said it (paraphrasing), the cartridge to transmit perfect information by moving up and down frictionlessly to allow for correct VTA as the groove modulates.

This in turn consist of two factors the geometry and the maintenance thereof. Geometry is the initial location (for the lack of a better term) of the tone-arm pivot point, stylus contact point and center of rotation of the disk, such to achieve Baerwald or Stevenson setup (or whichever one you believe to be best) and including optimal azimuth and VTA. Maintenance is the ability to prevent outside factors such as vibration and noise to change the optimal geometry.

Now to separate and isolate the arm pod from the platter, in perfect world, seems to address the maintenance issue. If the arm pod is isolated, any vibration from the motor or bearings will not be transmitted to the tone-arm or stylus.
This raises the question how is the arm pod accurately located in relation to the platter? Many of the systems in this thread show the arm pods simply placed alongside the platters with no means of accurately locating relative to each other (this is an appearance based on the photos) clearly these tone-arms are properly setup, but how accurately (initial geometry) and what prevents them from moving over time?

Ultimately, the arm pods must sit on a surface that is shared with the platter. The platter is isolated from this surface by pneumatic footer or other method, which no doubt prevents the platter vibrations from transmitting through the surface back to the tone-arm. But now since the platter location is no longer rigidly held relative to the tone-arm pivot, other environmental factors, such heavy footsteps on the floor or ambient noise, can cause these distances to change momentarily (vibration) or permanently (until readjustment). Is the arm pod as an island truly ideal?

A rigid location of the platter vs. the tone-arm pivot ensures optimal geometry, and high mass plinth minimizes the impact of vibrations and noise from the platter. Then isolate this assembly from the room. Is this approach not superior?

Hi Nick sr,

I have little interest/knowledge of scientific possibility (trying Hif Tuning fuses gives one example of why this is more fraught with options than seems scientifically likely!). However, wouldn't the answer to your ultimate question be: 'that depends on the stability and inertness of the plynth - on which the armpod rests and from which the tt is decoupled?'

Dgob, that'd be my view (and hence my reference to the seismic stand from Townshend). All of this (legitimate) concern with resonance has to deal with an originating source for the same(either airborne or transmitted via stands or gear, or as a function of playback itself--say in the case of a warped lp, or one that is not damped/clamped). Dealing with the resonances always comes down to the necessity of keeping the cartridge (the stylus, actually) "absolutely" stable. Read the accompanying text for the Rock 7 TT in the Townshend link previously given.

That said, the assumption is that the arm, pivot assembly, etc, are capable of minimizing the effect of any resonance that had been decoupled by the stability of good plinth design, that is, whatever resonances are "left over". Those "left over" resonances are either airborne (and some here suggest that those are minimal to non-existent in their effect, but I suspect that depends on the gear involved) or are generated by the physical effects of playback (again, warps, off-centers, and unclamped/damped lps).

One of the observations made by Townshend is that (at least) to date, the bulk, if you'll pardon the pun, of high-end TT design has dealt with resonances by increasing the mass of the plinth, and in some cases of the integrated plinth stand (say as in the case of the Caliburne/Continuum). You look at most of the really expensive TT gear and the one thing that is inescapable is that it is massive. Another way to deal with the issue of defeating vibration is to shorten the chain of resonant materials/connections (equivalent to fretting the string on a guitar)--a shorter tonearm for example (which involves other problems, one of which is the fact that it requires a different level of energy to set it vibrating).

But Townshend has been dealing with the issue in an entirely different way and that is by damping the headshell. In terms of resonance control, I think a simple illustration should suffice. Imagine a piece of 3/8" or 1/2" steel tubing that is four feet long and has one end clamped into a vise. With your finger you can take the free end of that tubing and push or pull it down a fraction of an inch and let it go and it will resonate. That free end of the tubing is behaving like a tonearm hanging out there over the record supported only by the most sensitive of supports, the stylus. But if you clamp down the free end of that tubing and apply the same force with your finger on the center of that tubing, the tubing will not move. It will take a substantially greater amount of force to move the tubing and the vibration and an order of magnitude greater amount of force to keep it vibrating.

Methinks Townshend is on to something, and he's been doing it for awhile.

Nick_sr,
The approach you describe is a common one and has been in use by different manufacturers for decades.
This thread is simply proposing a differing approach albeit one which still maintains the geometrical relationship between tonearm and turntable.
No-one here believes movement in that relationship, should be tolerated?

Halcro, I am not opposed to your approach, in fact I find it attractive. Your idea of the concrete arm-pod seems like a fun DYI project that I have considered for use on SL-1200 table. But that got me to analysing this approach and the big hurdle I see is locating the arm-pod.

Really my question is how can you guarantee this geometric relationship when considering using a Baerwald type set-up. With this type of setup we are taking about degrees of precision in fractions of milimeters. I have trouble seeing how simply placing, with out any means of mechanical fine adjustment, an arm-pod on flat surface(albeit very diligently and carefully)can provide such a degree of precision. Can you explain the approach you use?

One Idea I came up with would be to have mounting locations machined into the base used. But in doing so you then be coupling the arm-pod and turn-table to the mounting surface, and you would essentially be back at square one.