Skeletal vs Plinth style turntables

This is/was essentially my longstanding argument with Halcro vis a vis outboard arm pods.

Lewm seems a nice sort of guy but I can't bring myself to continually explain why his analogies are often theoretically inappropriate.
In fact Lewm, over the years has demonstrated a clear preference for 'theoretical' analyses over actual 'listening' experiments.
Virtually all the turntables I have listened to over the last 40 years have had a plinth and firmly connected armboard...
In fact I have just such a table mounted on exactly the same wall-mounted shelf as my skeletal table so I can actually LISTEN to both versions sitting on exactly the same "row boat"....

Here is the issue in mechanical engineering terms. It is not a lot different from the steering and suspension of a car.

In a nut shell:

the plane of the platter must be consistent with the plane of the cartridge. As the arm moves the cartridge must remain in this plane. Since the platter must revolve, there can be no slop in the bearing such that the platter can deviate from said plane.

As the arm must be set at a fixed point, it can then be seen that if there is any difference that occurs between the point of the arm and the surface of the platter that is will manifest as a coloration of some sort.

For this reason, the coupling between the surface of the platter and the locus of the cartridge cannot have any slop of any sort. To this end, the coupling between the bearing and the base of the arm must be as precise and tight as possible; IOW of a singe piece which will not respond to vibration, as if any differences can occur they will be interpreted by the pickup as coloration.

What this means is the more dead and the more rigid the plinth is, which also holds both the arm and the platter, the better the 'table will sound.

Now there is essentially nothing in Atmasphere's Post that I disagree with..
In my case, the rigid plinth is the wall-mounted shelf which is disconnected from any wall and floor Structure-Borne feedback...and that is really the most common problem with most turntables' support systems.
They are usually connected to racks sitting on suspended wood or concrete floors which are structurally deflecting under their own weight as well as live loads. These structural deflections induce low-frequency soundwaves into the suspended floor systems which are often below 5Hz and this low-frequency 'movement' cannot be stopped by racks or plinths.
That's why specialised stands designed to cancel out 2-5Hz Structure-Borne movement are used to support electron microscopes.
Air-Borne feedback is virtually a non-issue in all but a few extreme examples.
Once your rack and plinth are experiencing 2-5Hz structure-borne movement....you are on the Titanic and thinking about the safety of individual row boats..for one thing is certain....
The ship is going down...👀

Once again, you've written nothing that comes remotely close to changing my mind about outboard arm pods.

Dear Lew.....my mate...😍
It is not my desire to change your mind about anything...
I know better..😏
I simply use my ears and listen to actual examples BEFORE I blindly theorise..
Chances are I'll be back in the States before you make it to Oz..❓
If there's no Fosters there...a nice Chivas might have to do...👍

Hi Chris,

Glad to see you're off the DIY and enjoying the music...as Raul used to say?
Here is a 'suspended' nude Victor TT-81 design using the same idea as your coupling 'plinth'.
It all depends on what one 'means' by a plinth?
If an added shelf sitting on a shelf qualifies as a plinth....well, that's exactly how a turntable plinth acts.
If one removes the 'added' shelf (plinth)....could someone please explain the differences to the mechanical and structural functionalities?
I do appreciate the added 'warm and fuzzy' feeling this can impart together with the ability to mechanically fix the tonearm pods if their weight is insufficient....but apart from that...👀❓

Thought I might just share this image of a cutter on a 'shelf'....?
I think the emphasis on the mass and fixity of the cutter arm compared to the platter shares the thoughts on my Copernican view of the turntable system?

Dgarretson,
The big Micro SX-5000/8000 turntables are well respected but I've never been a fan of their arm-board cantilevered mounting systems.
Here is an example of a DIY project using the Micro system.
The structural integrity of the armboards fixed onto stainless steel poles via friction becomes less and less convincing the longer the cantilever becomes to support 12" arms.
The flexural micro movements in the armboards increase according to the square of the distance of the cantilever whereas there are no deviations in a mass-loaded fully supported armpod.
The fact that these (and others like them e.g. Raven) work....is perhaps an indication that actual micro-movements are still too tiny to be destructive..?
However....like my mate Lew....I just don't like the 'theory'...😎👀

I must be dreaming.......

Hi Parrotbee,

What Halcro says then explains why people like Mike Lavigne are using very expensive microscope stands in their systems.

If you talk to those who have changed to a wall-mounted shelf or active isolation stand or concrete slab-on-the-ground installation....they will likely express amazement at the reduction in noise-floor and the silent 'blackness' they now hear through the turntable system.
My vinyl playback system is quieter than CD...😎
An easy test for any turntable whether mass-loaded, suspended, plinthed or plinthless....is to place the stylus on an unrotating record and gradually turn up the volume of the preamp.
If a droning feedback sound commences and increases without further volume turning.....you are hearing Structure-Borne Feedback through your floor and/or rack supporting medium.
If you are able to turn your volume to maximum with total silence (even when lightly tapping the plinth)....you are probably free of feedback issues. 😘
Good luck....

Did someone say....plinth❓
Or plinthier
Finished
He goes on to say....

The JVC TT-101 drive unit is now installed in 40" tall, 280 lbs (!), solid birch plywood, and using the Zeta tonearm and EMT HSD-6 cartridge, This is now the best TT I have ever heard, bar none (including the Kuzma Stabi XL4 with the airliner air bearing arm and Dynavector XV-1 cartridge). The sound-floor is 'Dead Sea' low, background is pitch black, the tonality is accurate (meaty and full bodied) and the dynamics are explosive. The top end is creamy smooth (speed stability). I am very happy I went ahead with this project...

...a stock Lenco starts with numbers like 60 dB S/N, wow and flutter at 0.6% and with a 4 pole (!) motor when the JVC TT-101 is a core-less motor with 75 dB S/N (DIN B), 0.02% wow and flutter. One can argue about torque differences and cartridge drag on transients, but then how much torque do you really need?!? One owner tested the TT-101's speed stability with a laser when 3 tonearms and cartridges were mounted and playing at the same time and got zero deviation. Compared to my previous Oracle Delphi Mk II, all the micro dynamics that the Oracle excels at, are there but with even extra air and detail. However the Oracle sounds like a CD Player compared to this TT. Watered down, anemic and lacking harmonic completeness, meat/substance and macro dynamics.

Atmasphere,
It appears to me (from the photo of the lathe) that the platter support is inside the supporting base which must also enclose the drive system.
The cutter appears to be mounted on a 'rail track' fixed to the surface of the base which allows positioning and clamping of the cutter machine.

I'm not sure I follow your directly fixed arm description for my set-up...?
Could you perhaps elaborate....👀❓
I tapped the armpod and shelf (plinth) with a metal object whilst the stylus was on a stationary record...and the tone of both was near identical.
Whilst no sound was heard through my speakers when the shelf was tapped...a very slight 'tap' could be heard from the midrange driver when the armpod was tapped.

Pryso,
I imagine that the Victor TT is simply 'sitting' on the plywood plinth (as it sits on my stainless steel cradle)....but I can't envisage that the power cord exits at the base of the 'coffin'...❓
There are probably holes in the rear of the plinth for the exit of the power cable and also any tonearm wiring.....although with most modern arms the cabling is above the plinth.
Otherwise Chris may be correct.....there is a large door at the rear for the storage of beer....😜

Then I discovered his own Apolyt table used armpods.

LOL Chris...😃
Audiophiles are just funny (strange) people.....
Even rational university-educated audiophiles can make claims and statements without submitting one shred of corroborative evidence.....
And the sad thing is....these statements (or really beliefs)...are often accepted by the masses and treated with the same gravity as solid evidence-based science...😥
Take for instance Richardkrebs who the Professor (Timeltel) humourously taunts...
Now I like reading Richard's contributions here and he has undeniably made contributions to the turntable playback system (particularly in regards to Technics SP10 DD decks)....but

1) Perfect DYNAMIC speed stability. No drive system meets this and passing the (in)famous timeline test is zero guarantee of dynamic speed accuracy, only average speed accuracy.

here we have an educated, trained professional stating that a repeatable and accurate scientific test should be ignored because it does not tell us what occurs BETWEEN every record revolution....
All manner of inexplicable and unimaginable oscillations could be occurring BEFORE the laser flash of the Timeline hits the exact same mark EVERY revolution...👿
But Richard need not provide any evidence himself of such malicious oscillations....
The fact that he can IMAGINE them is good enough to spread doubt and discredit the only scientific device which was able to prove conclusively that Stylus Drag was a fact...in fact..👀
Emboldened by the audiophile armour of theoretical hypothesising....

If this heavily modulated force is sufficient to slow a weighty platter of considerable inertia, would it not also be able to "tilt" a free standing pod even, if it is substantial?

He forgets that the very device which he disparages (yet which proves the existence of Stylus Drag)...is also the device which answers conclusively his unsupported questioning of the free-standing pod....for if there were any movement in the pod itself or the tonearm (as the Professor rightly reminds us)....the Timeline laser would unmask it mercilessly...😜
And so for once...justice is done...👍

Richardkrebs,

The timeline test is showing that your TT is working correctly but do you honestly believe that its servo has some sort of preview of the upcoming modulation and reacts predictively? Of course not, it REACTS to a slow down and corrects.

This is what I mean.....
You present not a shred of scientific evidence to prove what you say or disprove what the Timeline shows....
Yet you reach a positive conclusion stated with precise conviction....

I do not understand how the time line test proves that the pod is not moving? All it is measuring is the platter's speed.

If this is true....I fear that you do not understand the basic physics of the question you pose.....

Richardkrebs,
The Timeline works by detecting stylus drag which is caused by friction.
To make an armpod move via the stylus/tonearm it must be solely by the friction (stylus drag) which is your hypothesis....
You need to understand and appreciate things like the mass, density and the inertia of the tonearm pod. Then you need to understand the disposition of the centre of gravity of such an item and the shear stresses which need to be transferred through the cartridge/tonearm to the fixing plate to then be converted to a bending-moment force sufficient to overturn such a mass about its centre of gravity.
Before any of that occurs....the frictional forces of the stylus in the record groove will have ground the record to a halt...and possibly into the dust...
But common sense will make this obvious to even lay folk....

Sigh......😖

Further to the above
02-10-15: Richardkrebs
I do not understand how the time line test proves that the pod is not moving? All it is measuring is the platter's speed.
A basic understanding of the physics involved would help.
Halcro's TT is a direct drive Victor 101. This turntable employs active speed correction using servos. The error correction detection can only measure the difference in relative speed between the base and the platter - those who have studied engineering, physics and mathematics at university would recognise that this a closed system.

The POD exists outside the closed system, and as such if the POD is moving, the servo correction cannot be correcting for this outside force as it is not in the measurement loop.

Therefore if the POD is moving, theoretically, it would reveal itself in the timeline test.

Did I just awake....👀❓

Wide awake now Chris....👀

Now Henry can confirm better, but if I recall he said that the timeline on the Raven turntable moved; but that it moved slowly and consistently. This implied that his turntable although not right at 33.3, maybe a little above (line going --->) this way or below line going (<-----) this way, the speed was still stable. So for purposes of enjoying records - just fine. Is that right Henry or am I blowing smoke out my ears ?

No smoke blowing here Chris....you got it..👍
In fact the drift to the left (indicating slightly less than 33.33rpm), whilst registering on the Timeline...produced this on the Feikert Platter Speed App.
Compare that to the VPI Direct and you can see that the Raven measures better than the VPI Direct on the Feikert App whilst the Timeline shows its slight inaccuracy.

Not quite sure what you're asking me for....❓
Before Basephysic's succinct Post...I had contemplated filming the Timeline on the Raven whilst I slowly pivoted one of the tonearm boards to demonstrate the laws of physics...but as can still be seen.....there are those who will develop their own 'physics' to explain away any evidence which collides with their views of the physical world..😥

Life is just too short...😎

Sorry Aigenga,

I should have been more explicit.
I was answering Chris' question about the Raven and its 'slight' retardation when viewed against the Timeline and then compared it to the Feikert figure for the same thing.
What most people don't realise (including apparently Michael Fremer) is that the Feikert App is primarily designed to measure and indicate Wow and Flutter. It does this against a benchmark tonal frequency recorded on a test disc of 3150Hz. The closer the measured frequency is reproduced to 3150Hz....the closer it indicates that the platter is spinning at precisely 33.33rpm.
For all the other figures in the Feikert App.....the Raw and Filtered Deviations....they are simply measured against the 'actual' platter speed regardless of how close to 33.33rpm it might be...?
For instance..if your platter were spinning at 31.06rpm but had little Wow and Flutter...the Feikert App figures would show -0.01%/+0.01% Max Deviation.
It simply doesn't care much what your platter is spinning at...😢
Would you be happy with this...❓👀
In the case of the Raven speed...the Feikert shows 3149.4Hz (0.6Hz below the correct speed of 3150Hz) against the VPI Direct speed of 3154.5Hz (4.5Hz above the correct speed of 3150Hz).
Here is Harry Weisfeld talking about the vintage DD turntables in relation to his VPI Direct and he makes a valid point about the weaknesses of the arms often bundled with the old classic decks.
Until you've heard a TT-101 with a really great tonearm (as you know)...and separate armpods are a great way to hear this.....you haven't really heard how great a table this really is...😎

And despite having 35 years of technological supremacy over the TT-101...together with the Thingap revolutionary motor which claims to possess zero cogging....Harry still can't match the performance figures of the big Victor...👀❓