For those who are unfamiliar with his name, Pierre Lurne has been an integral part of cutting edge turntable design since the late 1960's. Pierre designed his first arm design in 1968. He later was commissioned to do design work for a then major player in the audiophile turntable market. Pierre is responsible for the now legendary T3 arm which sat atop a well known reference table. The T3 design dates all the way back to 1978. Pierre later went on to design and produce the T3's little brother the T5. The T5 is also know as the SL5 under the Audiomeca name.
In the years since, Pierre has designed several turntables and arms marketed under the Audiomeca name. Starting with the Audiomeca J1 turntable in 1979 and his (now) familiar SL5 linear tracking tone arm, then proceeding to his J4 turntable, Pierre has created a legacy. In 1989 and after many years of research, Pierre debuted the Audiomeca Romance turntable and his latest arm design, the Romeo.
After nearly twenty years of production, Pierre has refined his design once again. His latest creation is the Belladonna turntable and the Septum tone arm. In the forty year process of designing tables and arms, Pierre has formed some very strong opinions regarding turntable and arm designs. His design thoughts are more than simple opinions. He bases all of his designs on his knowledge of the elemental, physics. In Pierre's own words, "I have worked a lot on these points (basic physics, vibration control and channeling) which seem so forgotten in our analogue field. After all this is Physics again. I base my work on strong physics foundations but Physics is not enough, experience, time, love, and even luck all play their role.". For those of us who are truly into high end turntables, we know how damaging vibrations can be to the fragile signal that our cartridges pick up.
As you will read, vibrations go far deeper than isolation or
absorption. Vibration control at its
root should be the focus of proper turntable design. The flow and proper
draining of any noise within a turntable is absolutely critical to produce an
uncolored signal from a piece of vinyl.
Though Pierre's position paper submitted within is primarily about turntable and platter design, his philosophy extends to tone arm design also. Later this year I will have the pleasure of spending some time with the Septum tone arm. This should prove to be a very interesting experience. I look forward to mounting the Septum to my Opera LP5 and comparing it to my Dynavector 507 MkII. With some luck, I'll be able to have Pierre write a subsequent paper on tone arm design.
So without further adu, Here are some thoughts on turntable
design from the master designer, Pierre Lurne.
The platter of an analogue turntable is primarily in charge of handling the vinyl record, to ensure its centering and horizontality, to spin it at the right speed with a high degree of accuracy and silence, and to deal with various external vibrations as well as those generated by the tracking and bearing. A much more difficult task than one would suspect. The platter acts as the heart of the machine. All of the other components ultimately play a supporting role and are comparatively of a lesser importance.
The Usual Bearing
In fact, the behavior of the spindle, hence of the platter, becomes quite chaotic. It rocks and chatters inside its mechanical play and is subject to all secondary microscopic movements of any dynamically imperfect physical body spinning on an axis. As a final result, varying pressures and a whole series of constantly changing resonances within the bearing are at work, affecting the platter rotation and producing a result that is all but smooth.
If the platter is well balanced, the situation improves but the basic instability remains. This dynamic balancing can only be performed in a way that can be witnessed at your local tire shop - a very rudimentary method.
With so many drawbacks, it is no surprise to get a rotation of poor quality. Spinning the platter by hand and releasing it always produces a very short "run down time". This clearly demonstrates the high level of effort and friction within the bearing that the motor has to overcome, not too mention the increased power consumption and noise produced. All things being equal, the simple comparison with the run down time of another platter shows without a doubt which platter/bearing combo is better designed, or manufactured (providing they have both been broken in, well-cleaned and duly oiled).
The stylus inevitably tracks all noises, friction, efforts, micro-movements and resonances. The music becomes blurred and constrained, the dynamics lose punch and low frequencies sound the same, becoming badly defined
In Physics, such a platter cannot be considered "Perfect". It
is not a "Pure Mass". Note that Direct Drive turntables belong to that category.
A Better Bearing
Unfortunately a pendulum is so created which limits the improvement. Its own resonance frequency is very easy to calculate (school basics). One could argue that it cannot oscillate for the spindle maintains the sleeve. This is not the case. In mechanics, the "zero play" does not exist. To be effective, any spinning movement needs a "mechanical play" between spindle and sleeve or it would be at a high risk to jam. This is even called "the working play" or "the functional play". Parasites randomly take place in this tiny interval as soon as the rotation begins and do not stop in steady speed mode. Yet again, vibrations, chattering, friction and noise are all tracked by the stylus and once more, there is a bigger demand on the motor and more noise is produced as a result.
The dynamic balancing can be more accurately performed with the same "tire shop method" or with the "tilt test" which gets rid of bearing friction. Placed upon a thin spindle for example, the platter tilts in the direction of the excess of mass. Then, a few holes are drilled there and under the platter edge, removing some mass. The tilt angle decreases and after a few trials, the platter finally stays still and adequately horizontal with the center of gravity aligned on the geometric vertical axis passing through the point of rotation, the pivot, just above.
But again, the accuracy is still insufficient because, hole after hole, the off-centered mass decreases as does the tilt angle which finally becomes too small to be located precisely enough and consequently, nobody is able to know exactly where to drill the holes. Although the dynamic balancing is slightly better, it is far from being complete. The run-down time is improved as well but it remains rather short. On a lesser degree the centrifugal force still tends to eject the platter away which results in the same nasty collection of pressures, friction, noises, vibrations and so on, all readily tracked by the stylus.
Once again, the system cannot be described as "Perfect".
It is not a "Pure Mass".
The few other manufacturers using the inverted bearing throw
away its advantages by either placing the point of rotation too high (pendulum)
or too low (instability) and/or by using too long a sleeve or a "2 sleeve
bearing". This gives the bearing several axes resulting in friction and noise. We recall that a single line is defined in geometry by 2
A Question Of Philosophy
The audiophile always looks for the best. Step by step, as his
experience and knowledge proceeds, he improves his audio system, trial after
trial, and goes through all hopes, satisfactions and disappointments. The game
Logically, the audiophile favors the source because the
perfect electronics and speakers are not able to recover something already lost.
"All that is lost from the source is lost forever". The turntable acts as the
source of the complete audio system and the platter is the heart of the
turntable. On the other hand, arm and cartridge also make an all–important
combination, a whole. They never solely track a record, they always track
another whole, that is, the record and platter combo and how a poorly designed
platter damages the musical quality has just been discussed above. To achieve
real dynamic range, transient response, deep bass, image, clarity, credibility,
emotion or any other musical characteristic requires an absolutely neutral
A Question Of Physics
Neutrality stands on a fine line between pleasant low
colorations and over-damping. Neutrality is the very first quality of a complete
player, which in addition, acts as the source for the entire audio system.
Mathematics demonstrates that neutrality can be satisfied by
Pure Mass. Here we are. In Physics, the concept of Pure Mass is defined by a
particular case of the general balance of any given body. What is that exactly?
Center of Gravity is a clear notion. It is almost intuitive. Everything has a Center of Gravity (or Barycenter) that we can roughly locate and therefore claim, "It is there".
A body is considered a Pure Mass or "Perfect" when it is
perfectly balanced on one point, the Point of Rotation, which is also its Center
of Gravity. Point of Rotation and Center of Gravity are coincident. The
Ellipsoid of Inertia becomes the "Central Ellipsoid of Inertia".
This highly aesthetic and particular case gives the body a number of exceptional dynamic properties. In perfect dynamic balancing, the body has no will of its own, no signature and no personality. It is "dead", neutral. It is obvious just how significant a role this notion of physics will play in arm design. Such a perfect system also benefits from secondary advantages, true natural gifts: It reacts perfectly to any input of energy, any parasitic force originating from outside (vibrations, belt drag, arm tracking force, resonances etc.) is reduced to a minimum and all microscopic movements are cancelled.
Such a smooth rotation obviously means that the motor has little work to do, resulting in decreased noise. It merely provides the slightest top-up to keep the platter spinning. An old tip of the engraving engineers was precisely to reduce the drive motor torque close to the breaking point in order to improve the signal noise ratio and the rotation quality of the lath.
So we are able to see here that the correct application of the
Pure Mass concept brings various benefits with it including neutrality, quality
of the rotation, less motor noise, less bearing noise, lower wear rates, reduced
significance of critical leveling, no complex resonance and so on.
To summarize, the "Perfect Platter" would require an inverted
bearing principle with only one low-down, short ring as sleeve and the General
Center of Gravity coincident with the Center of Rotation - elegant and simple.
A Little Secret
Obviously the laws of physics are demanding but they are the laws of God and remain un-changing. One could nevertheless maintain that good physics are merely the foundation of good design and that time and experience, love and even luck are what add the final touch in producing an outstanding analogue source.
Now the question is: Would you prefer a well-designed platter
or a common one affected with all of the defects described above?
From now on, the virus is growing in you and every time you
will see and listen to a turntable, even a great and expensive one, you will
hear a little voice murmuring, "Remember just how much better it would be if
physics would be respected".
There are hundreds of other parameters involved in platter
design but even so, this cannot be used as an excuse for defects in design. Even
with the utmost care to sound propagation, correct grounding and to the acoustic
impedance of the materials etc., all will be lost or at least corrupted if a
weak point sets the overall limit of the results.
Whether it is light or heavy, made of aluminum or composite,
designed as one solid piece or as sandwiched components, there is basically only
one way to design a platter.
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