This has absolutely nothing to do with the differences between DD tables and idler tables, but IMO a cone-shaped footer can be an asset IF one first determines the loci of standing waves on the shelf (which would be based on the resonant frequency and is best located with a stethoscope) and then places the tip of the cone on a vibrational node (i.e., a point where the shelf is not vibrating). This would then prevent the shelf from transmitting vibrations up into the equipment, because the equipment would only "see" the null points in the shelf. Like you guys, I don't quite see how a cone will prevent transmission of energy in the other direction. However, is not a diode a one-way device? Ergo, we have a mechanical diode. Maybe the term "diode" is not semantically appealing in this case. |
Cones have the shape of the electrical symbol for a diode but this doesn't mean they act as (mechanical) diodes. Btw, why should mechanical devices act like electric devices and vice versa? Personally I think the mechanical diode theory is not a scientific one.
Chris |
As much as we wish they were, cones do not act as diodes. |
Interesting points Lew. Wish I remembered more of what I was supposed to have learned in Physics, i.e. energy travel.
From what I understand from a discussion with Albert, his brass rod contacts the bottom of the bearing housing under the motor. How much energy is then transferred downward to the iron block sink, thus not upward through the spindle, platter, and record I have no idea. But it is easy to accept that this will have some positive effect.
Part of my lack of understanding is the assignment of a diode effect on energy travel to some isolation devices by a number of hobbyists. For example I think the effectiveness of "tip toe" style devices relies more on the concentration of mass than on transmitting energy in one direction but not the other. Like the old story that a 120 pound woman in high heels exerts more pressure per square inch than an elephant.
So for now it seems we are left to trial and error in our own systems. |
Hi Lewm, the idea of dampening of spurious vibrations is a nice one, but you actually don't need high mass to accomplish this! What you need is a low impedance path for the redundant kinetic energy, which should have a constraint layer construction. Such a construction is not by definition high mass --> look at the theory behind the Symposium Ultra Platforms.
Chris |
Here's the way I try to think of the difference between an idler and a DD as regards plinth design: In the idler, the motor and idler itself are "external" sources of noise and vibration, whereas the rotation of the platter and the bearing can be just as inherently silent as that of a belt-drive table. A high mass plinth can drain away the motor/idler noise before it reaches the platter/bearing. That makes sense to me. On the other hand, in a DD table, the motor is a priori and inseparably associated with the bearing/platter. In a way, it's a closed system. So it is not obvious to me how a high mass plinth per se can efficiently interdict the transfer of noise to the platter from the motor. That's why I admire the thinking that has gone into Albert's plinth; there is an attempt to drain spurious noise into a heavy iron block via a threaded rod that contacts the base of the motor/bearing assembly. So instead of going upward into the platter, the spurious motor and bearing vibrational energy has a low impedance path downward into the iron block. In theory, it makes a lot of sense and similar strategies could be adapted to other DD tables. The high mass plinth may just be icing on the cake, to dampen chassis vibration and provide a solid base for the total structure. (I guess other plinth-makers have used a similar strategy to Albert's; I am not assigning a patent on the idea.) |
I previously posted a question on the need for a massive plinth for the SP-10 on a couple of sites but did not receive any definitive replies. While there is extensive information of plinths for Garrards, Lencos, Thorens, and other rim-drives, there is not nearly as much for Technics or other quality DD tables.
My premise was that because of the mass needed for rim-drives, most DD owners assumed that would benefit their tables as well. But now we have more information and extremes are reported. At the low mass end is Raul who's SP-10 utilizes only an extension for arm mounting and three suspension feet, while the high mass approach is represented by Albert Porter and Oswalds Mill, among others.
So obviously both approaches can work. Too bad no one has reported on a direct comparison. |
Hi Raul, I didn't know that. I thought a custom made plinth is a necessity with the SP-10 to sound great. Stock SP-10 is very good, but SP-10 + custom plinth = great. But now you are saying a bit the contrary and it's an eye opener for me. Do you also concur with the hypothesis that a plinth can actually add coloration (or drain away the life out of the music)? In this regard Thom Mackris is quite right: it takes a lot of expertise to design a dedicated plinth/base that brings out the best of the turntable without the draw backs (there are many variables to deal with: mass, dimensions, materials, structural design, attachment of the turntable to the plinth, etc.).
Chris |
Dazzdax, You raise an interesting question, and I am glad that Raul responded with his experience. One logical reason for a heavy plinth on the SP10 was put forward by Mark Kelly, a person whose opinion commands respect. Mark noted that because of the torque of the SP10 motor and that of other tts with torque-y motors, a heavy plinth will serve to counter the tendency of the motor to twist itself and the chassis frame to which it is attached. I have thought about this a lot; I am not sure how or whether high torque motors would create an audible problem, once the platter is up to speed. (The full torque of the motor is only applied during the instant after turn-on when the platter is still at rest, I would think.) Albert Porter's plinth deals with motor/bearing vibration in a novel way that might mitigate the need for a super heavy plinth. (Go to the Sound Fountain website to see a depiction of Albert's idea.) |
Dear Chris: +++++ " why does the SP-10 without this custom plinth sound that bad? " +++++
I don't know where do you read that statement. I'm using one of my SP-10s with out that custom plinth ( only three pneumatic AT footers/isolators ). I heard it with at least two different plinths and IMHO and in my system sounds better with out that plinth. I already heard too some other SP-10 ( on other auduio systems ) with custom plinth and with the Technics plinth and " sounds " good but I prefer mine. Now, the SP-10 with out plinth looks not very good but works fine.
Regards and enjoy the music.
Raul. |
Your analogy between a turntable plynth (water down the drain) and enclosure-less loudspeakers is faulty. A loudspeaker is a transducer, a turntable is not. The cartridge is the transducer. So, maybe the question should be "does a cartridge need a body?" I have no experience with nude cartridges, but I know they have their proponents. |
Ultimately, you're talking about draining energy from the bearing/platter interface in this discussion. In this regard, the materials chosen are as important as the actual mass.
There are different ways to solve the problem, or alternatively, to screw things up.
For example, high mass with ineffective energy transmission (stores energy) is going to have a resonant signature at some frequency. It will be the mechanical equivalent of a capacitor having a high dielectric coefficient with resulting blurring and resonance. Low mass done poorly can be equally compromised.
As is typical in audio, it's the design/implementation of a particular architecture rather than the chosen architecture that makes the most difference.
All of my experiments have shown me that in a non-suspended design, high mass done right has an inherent advantage, but it needs to be noted that this is the path I've been led down, so I have a bias in making this statement.
The unfortunate reality (in terms of arriving at shared, transferable, reproducible results) is that you need to consider the experiences of SP-10 owners in the context of their entire system, their setup, and of course, their turntable shelf/stand.
I like to think a of the shelf/stand combo as a part of the turntable and try to be very careful in drawing conclusions because of this.
Context is everything, but you all knew that ;-)
Cheers,
Thom @ Galibier |
Thsalmon: what I mean with a plinth is the often rectangular box (= base) that accommodate both the spindle encasing for the platter and the tonearm. For example the "nude" Technics SP-10 without the dedicated obsidian base already comes with an encasing (as you mentioned) made from plastic (I didn't know that, I thought it was made from some sort of metal). I've read here at Audiogon that a custom made plinth is a necessity to bring the best out of the SP-10. My question is: why does the SP-10 without this custom plinth sound that bad? You can use some of the graphite feet or the Walker Valid Points for under the "nude" turntable for decoupling purposes.
Chris |
We still have a nomenclature problem here. A "plinth" is simply any type of base or pedestal. All turntables have a base of some sort. The Simon Yorke's plinth is its' round base. The LP12's plinth is the wood-trimed case that supports the suspension, and the Rega plinth is he rectangular board to which the bearing, motor and arm are mounted. The Technics has a plinth too, it is the plastic case to which all of the guts are mounted. I think the original question really applies the the need for some type of mechanical isolation device for a turntable. |
Mark, yes I mean the spring suspension. A turntable with spring suspension needs a plinth to accommodate the springs of course. turntable without a spring suspension don't need a plinth theoretically --> just look at the Simon Yorke designs. You can make a dedicated plinth for the Yorke turntable but I think that would not improve it's sound. In theory the Technics SP-10 also doesn't need a plinth because the motor/drive unit is already encased in a metal cage. You only need to use three decoupling feet for mechanical isolation, that's all. Of course you should make a separate tonearm base to accommodate the tonearm.
Chris |
Unless you've figured out how to get your table to float in mid-air you've got to set it down on something. A heavy inert platform - a plinth - will help reduce vibration and allow you to hear the record and the needle, not ambient vibrations. |
Unless I'm misunderstanding something here, by a non-suspension turntable, are you referring to something like an inexpensive Rega that doesn't have a sprung suspension? It still has a suspension, i.e. it's feet.
If you have a non-sprung suspension turntable, the plinth is what everything else is attached to. The motor is screwed to the bottom of the plinth. The bearing well is attached to the plinth and the tomearm is attached to the plinth. So decouple the motor. That's certainly possible. Maybe the tonearm, but I can't think of such a beast at the moment. But decoupling the bearing well from the plinth? How do you do that? The platter is then spinning like a top on a bearing well that isn't attached to anything.
So I wonder if I am misunderstanding what you are asking. If not, then the plinth is simply the structure other things are attached to. That's why it's necessary. Otherwise, it's like a human body without bones.
Have a nice holiday by the way! |
