A Copernican View of the Turntable System

Lew,
What you are hearing when you 'tap' on the shelf.....is the effect of the structural stresses within the shelf.
These stresses differ throughout any material depending on methods of support, locations of maximum and minimum bending moments, locations of maximum and minimum shear stresses and locations of all the various deflection points.
These stresses will also differ (in the same location) throughout the DEPTH of the material....normally compressive stresses at the surface, changing to tensile stresses on the bottom (reverse these for a cantilever).

These stresses will normally not affect the material's reaction to air-borne sound transmission.....most waves reflected or passing through.
Tapping a shelf to test for air-borne acoustic performance is similar to the infamous 'tap-test' employed on turntable plinths by some incompetent reviewers.
I liken it to the analogy of tapping on one's head to test for hearing ability? :-)

Regards...and peace

Thanks Halcro,

And I will of course feedback on my findings. I think the grounding issue really is a major one, despite my use of wall shelf mounting and experimentation with a number of platforms and methods of isolation. Walls rarely seem as neutral to vibration as I would wish and even wall mounting carries detectable vibrations - listening through my system within a fairly solid 19th Century English home. Along with decoupling tonearm and TT (arm-tower/pod), the use of pneumatic footers was (as I suggested) the most marked improvement to the quality of analogue reproduction in my experience: quality of system, hearing sensitivity and expectations not withstanding. That this is the case is simply beyond doubt for me and so my only questions are:

1. Does the decoupled arm/TT really offer the ultimate feasible set up? and

2. Will pneumatic decoupling of a coupled (or, 'plinth based') arm/TT from the grounding/platform really offer the ultimate feasible set up?

That's what I'll be looking into in a suitably empirical way and that's really all that I'll be able to report back on. What others choose to make of that or 'believe' will obviously remain beyond my compass.

As always...

I should just add that not all pneumatic supports offer the same degree of isolation and that my most positive experiences relate using to the Audio Technica AT616 Precision Pneumatic Footers in particular.

Dear Lewm: ++++++ " With the big Micro Seiki's, and since we are all about building new or modifying original products to suit our beliefs and desires, isn't is possible to get around their perceived problems with the armboard mount by using (i) an outboard armpod, or (ii) a modification of the original cantilevered design? Since those tables reportedly have many virtues (never heard one myself), wouldn't this be worth the effort? " +++++

I don't think is worth the effort because the MS RX-5000/8000 has more defects than virtues on design, IMHO is a faulty TT design and other that good lokking because the shiny weigthy golden platters there is nothing to admire but its marketing.

The design comes with out any TT isolation for external internal resonances/vibrations, anything goes and stay inside degrading the audio signal. The heavy platters ring like a bell, MS choosed to seat the cantilevered arm boards exactly at the plinth footers where these footers has no isolation and everything is transmited to those arm boards, the motor came from Matushita but the control circuit not only has poor parts but not a good design.

I bought mine because I was a newbie/roockie with the MS TTs that have behind an unjustified fame but we audiophiles are " believers ".

Today I really don't use it any more, I learned on those MS TTs.

Other persons " die for it ", well they like the MS distortions: not me any more.

Regards and enjoy the music,
R.

Dear Raul, What you write makes perfect sense. I note that most of the MS users have modified their tables to get to where they are happy with it. Along those lines, I would have thought that an outboard arm pod would at least defeat that very real issue you cite about mounting of the OEM arm boards. On top of that, I noticed that some guys use thick mats of various kinds, and other devices, to reduce platter ringing. Further, many use more modern motors, as even the real diehards agree that the MS motors are not so great. By the time one is finished, not much is as original. But I cannot criticize the result, because I never heard one.

One might say that we Lenco users do the same thing; many factory parts are typically discarded and replaced in a well tweaked Lenco L75, but we start with a $300-turntable that is fundamentally sound, not a $5000 (and up) one.