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Tonearm mount on the plinth or on Pillar ?

Folks,
I am looking to buy a custom built turntable from Torqueo Audio (http://www.torqueo-audio.it/). They have two models, one with a wide base plinth where the tonearm would be mounted on the plinth (as usual) and the second is a compact plinth where they provide a seperate tonearm pillar to mount the tonearm. According to them the separate tonearm pillar version sounds more transparent and quieter because of the isolation of the tonearm from the TT. My concern is whether seperating the tonearm from the plinth would result in a lesser coherence in sound ? Isnt sharing the same platform results in a more well-timed, coherent presentation ? Any opinions ?
pani
atmasphere's avatar
atmasphere
12,116 posts
 
Air borne vibration will hit the record/platter directly, as it also hits a plinth and arm. Any such vibration transmitted via the plinth will arrive after the event. How will this insure coincident behavior between arm and platter?
Again, for what, the 4th time? The platter and arm must move in the same plane and frequency, should there be any movement at all. Likely this would be airborne induced. If the base of the arm can move in a different plane or frequency, the result will be interpreted by the pickup as a coloration or noise.

For this reason the plinth must provide absolute coupling between the platter bearings and the base of the arm, and also must be completely dead (free of vibration) for best results.

In the case of an arm pillar you have essentially a poor plinth. This is because the mass of the pillar will simply not be in the same plane and frequency as that of the surface of the platter. Since the cartridge is essentially the interface, its stylus must make up the difference between the motion of the pillar and that of the surface of the platter. This insures that there will be a coloration. Please note that the platter does not have to be spinning for to be measurable.

As some others posted you are intuitive more than scientific in this subject.
No one of us audiophiles have a lathe at home but normal TTs but because in your  simple  " test " you say that appears a " coloration " then in any inferior/normal home audio system things must happen too. That's what you infere but can't prove it.

Oh I can prove it alright- and I reported how that was done. It certainly is intuitive and also scientific. Sorry I didn't record the measurements; at the time I didn't think anyone but ourselves would be interested.

Raul, if I might be so bold, you are accusing me of being intuitive and not scientific, despite the fact that I made measurements and my comments derive from those findings, while those my accusers have none!! Does anything strike you as wrong with that picture??

When we were developing the Atma-Sphere 208, we started with a plinth that was really terrible (the stock Empire plinth). We found that by treating it with damping materials, it got better, but was far better when we replaced it with a plinth that was machined of solid metal. The benefits were enormous- this made the machine far less susceptible to the volume of the stereo as it was playing in the room; bass was improved and so on.  At that point the plinth was machined out of solid aluminum 0.75" thick.

We found that by installing a brace between the the mount for the platter bearings and the base of the arm that there was further benefit.  Now if the pillar theory was correct this would not happen- improving the coupling would make it worse! This is science after all.

halcro's avatar
halcro
2,664 posts
 
Since the cartridge is essentially the interface, its stylus must make up the difference between the motion of the pillar and that of the surface of the platter.
"The motion of the pillar"......
There you go again. Nobody is claiming that a "moving pillar" is good but you have simply assumed that ALL pillars move because you yourself have used a 'moving' pillar (which you still refuse to disclose despite my three attempts to wrest it out of you).
A properly designed armpod sitting on a well isolated rigid base/shelf/plinth will NOT move despite your ill-informed protestations.
If I had an oscilloscope (and knew how to use one)....I would measure the three arms fixed to my Raven plinth and the three mounted on the armpods.
It would be interesting to see your arguments if these measurements contradicted your 'theory'....
halcro's avatar
halcro
2,664 posts
 
We found that by installing a brace between the the mount for the platter bearings and the base of the arm that there was further benefit.
Now this is illuminating and perhaps needs an explanation from you about what you believe could possibly be 'moving' in your 3/4" solid aluminium plinth?
In other words....what did the "brace" fix that was a weakness in the solid aluminium?
This is a structural and not a mechanical engineering question and requires a structural engineering answer....
thekong
203 posts
 

Hi Halco,


While I tend to agree with Ralph /  atmasphere, I think it would be interesting if you could do some tests.


To my way of thinking, the test can be rather simple, just lower the cartridge on a stationary platter / LP, then play music through the CD system, and measure the output of the cartridge.


If Ralph is right, then there should be more signal / noise with the stand alone arm pod. With this test, you can even see how high the volume needs to be before the stand alone arm pod is affected, if at all. Actually, if we only need to know the level of output of the cartridge, would a simple voltmeter be sufficient ?


Anyone see anything wrong with this simple test ?

fleib
1,124 posts
 

Thekong's suggestion brings up an issue we haven't addressed. What exactly is the source of this vibration, and what is its relevance?

Atmasphere, you talked about a motor producing 90 - 95dB of noise in the room and described the vibrations as room borne not air borne. This sounds more like a seismic event than music playing, as if a bus or truck drove down your street and shook the house. We not only have 90+dB of noise, we also have the motor vibrations which produced the noise.

If you consider the principle involved, that is any extraneous arm/platter movement must coincide, then why is using a plinth more desirable than a base?  The best plinths are those that do not transmit vibrations, but now we want transmission?

I think the answer is in the execution. A "properly" constructed pod will not allow movement in a different plane. The base will serve the same function as a plinth only with more affective isolation. A seismic event is shaking the entire table and platform and your set up was unstable with the pod.

Regards,

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