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Lew
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MessagePosté le: Mar 16 Fév - 05:36 (2010)    Sujet du message: DF for slate Répondre en citant

I have read most of the posts on this very interesting thread, but not all of them.  I did see where the DF for "slate" was a rather disappointingly low number.  As I have three turntable chassis' now up and running in very heavy slate plinths, and as I am very pleased with the results, I am interested to figure out why the measurements suggest I should not be so happy.  It immediately occurrs to me that slate from different sources can be very different in density and composition, so I wonder what was the source of the slate that was subjected to testing.  For example, I have a plinth made of Vermont slate (for my SP10 Mk2A) and one made of Pennsylvania slate (for my Lenco and Denon turntables).  The Vermont slate is much denser and much more "dead", for want of a better term, compared to the Pennsylvania material.  Another observation I have made is that slate reacts very differently if energy in the form of a blow or knock is imparted in a direction parallel to the layering of the material vs if the energy is imparted perpendicular to the horizontal layering.  Vibrations seem to be profoundly attenuated in the former case, but there is obvious "ringing" in the latter case.  So I also wonder how the test was conducted in that regard.  As Bryan seems to have recognized when he tested two different samples of laminated aluminum, this is a very complex subject.
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MessagePosté le: Mar 16 Fév - 14:31 (2010)    Sujet du message: Re: DF for slate Répondre en citant

Lew a écrit:
I have read most of the posts on this very interesting thread, but not all of them.  I did see where the DF for "slate" was a rather disappointingly low number.  As I have three turntable chassis' now up and running in very heavy slate plinths, and as I am very pleased with the results, I am interested to figure out why the measurements suggest I should not be so happy.  It immediately occurrs to me that slate from different sources can be very different in density and composition, so I wonder what was the source of the slate that was subjected to testing.  For example, I have a plinth made of Vermont slate (for my SP10 Mk2A) and one made of Pennsylvania slate (for my Lenco and Denon turntables).  The Vermont slate is much denser and much more "dead", for want of a better term, compared to the Pennsylvania material.  Another observation I have made is that slate reacts very differently if energy in the form of a blow or knock is imparted in a direction parallel to the layering of the material vs if the energy is imparted perpendicular to the horizontal layering.  Vibrations seem to be profoundly attenuated in the former case, but there is obvious "ringing" in the latter case.  So I also wonder how the test was conducted in that regard.  As Bryan seems to have recognized when he tested two different samples of laminated aluminum, this is a very complex subject.

Hi Lew,
I see this is your first post, welcome et bien venue.

Firstly, if you are very happy with the 'sound' of your decks, please don't let me discourage you from deriving enjoyment from them, paranoia is a very dangerous thing in hifi, and probably sells more equipment than common sense and logic. Very Happy

As you pont out, materials, although superficiously the same, can differ in their properties, I have mentioned that the measurements I have taken are with respect to the pieces of material I have. However, I think any piece of slate worthy of the name (and worthy of making a plinth out of) has to be homogeneous and crack free. The piece I tested was from a 100 year old roof tile. You may accept this as being representative, or not. Smile

When a material is struck, such as a plate or sheet, near its middle, standing waves are set up. These can (and will be) derived from the plate's dimensions, and whether  the plate is in free field or constrained at the edges. For a free field condition, the first, or fundamental frequency (mode F1,1) is when all edges are vibrating, but the middle is not. Other, higher modes are subdivisions of the plate's dimensions, always whole numbers. So, when a plate is struck, many resonances occur, depending on the sample's dimensions, as well as other things. If you strike the sample on its edge, you transform the sample dimensions from being a thin plate to a thick beam, which has very different vibration characteristics. It has nothing (or very little) to do with slate's morphology. Even though slate can be cleaved in planes, I do not consider it a layered substance.

Why slate is good, from a material property viewpoint:

basically because of its mass and stiffness. A piece of slate (or any similar material) the size and shape typical of plinths, will have three regions where vibrations occur, and are controlled by different phenomena. Up to its fundamental frequency (F1,1) the plate is controlled by its stiffness. Slate is very stiff, so scores well here. Next is a region between the fundamental frequency and the critical frequency, which is controlled by the mass of the plate. Again, although slate is not that dense, it can have a resonable mass.

Why slate is not good, from a material property viewpoint:

The third region, above the critical frequency, is controlled by damping, and just above the critical frequency is a region where, depending on the material's damping qualities, severe loss of attenuation can occur, to a point where the plinth becomes 'transparent' to sound! And the more the loss of attenuation, the wider the frequency region that this occurs in. The other thing to note is that the resonances will be either narrow and high (high Q) or low and spread out (low Q), or somewhere in between, depending on the intrinsic damping of the material (n). We know that n = 1/Q (at a resonance), so for slate, I measured the damping factor, n, to be 0.0174 for slate, so the Q will be about 5.8, but as Q = resonance frequency divided by the bandwidth of the peak, the lower the damping factor, the sharper the peak, the higher the peak will be, eventually becoming intrusive.

Adding damping to the slate is problematical. I don't yet know how this works, that is, how the damping factors and masses (or even volumes) of massive and damping materials interact. My best guess is that trying to damp slate is going to be a big problem.

Why something else would be better:

The 'best of all possible worlds' would be a stiff, massive material with very good intrinsic damping. Such materials as 'Panzer holz', filled polyester, and even aluminium laminate, have been suggested. These materials are anisotropic, and may point to a better product.

HTH, Lew. hats off
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MessagePosté le: Mar 16 Fév - 15:37 (2010)    Sujet du message: Slate/Ardoise Répondre en citant

How would you expect a material with properties of slate to "sound"? Where did the slate tile come from, geographically speaking?  Would you be interested in testing small pieces of slate from different parts of the US?


I yield to your obvious expertise in this area, and I have often wished there were someone around who could make analyses such as this.  I thank you for that.  I do have trouble with the idea that slate would behave in exactly the same way regardless of the vector direction of the force applied with respect to its "structure". (I hope we can agree that slate has an ordered structure; I used the lay term "layers" for want of a better word. In this way, slate is certainly different from Panzerholz or cement.)


It would be interesting if you could make an analysis of a piece of the plinth from a Kenwood L07D turntable.  It has the overt characteristics of a kind of cement or a kitty-litter concoction.
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MessagePosté le: Mar 16 Fév - 16:51 (2010)    Sujet du message: Slate/Ardoise Répondre en citant

Lew a écrit:
How would you expect a material with properties of slate to "sound"? Where did the slate tile come from, geographically speaking?  Would you be interested in testing small pieces of slate from different parts of the US?


I yield to your obvious expertise in this area, and I have often wished there were someone around who could make analyses such as this.  I thank you for that.  I do have trouble with the idea that slate would behave in exactly the same way regardless of the vector direction of the force applied with respect to its "structure". (I hope we can agree that slate has an ordered structure; I used the lay term "layers" for want of a better word. In this way, slate is certainly different from Panzerholz or cement.)


It would be interesting if you could make an analysis of a piece of the plinth from a Kenwood L07D turntable.  It has the overt characteristics of a kind of cement or a kitty-litter concoction.







If you send bits of slate (not too thick, about 100mm square is ideal) I will test them for you, no problem.

As to structure of slate, I consider it faily homogeneous. As it is metamorphic, rather than sedimentary, it is not stratified in the normal sense. It has cleavage planes, of course. I liken these to stars in the heavens, the stars are the mica crystals that randomly populate the slate. It is possible to draw a line across the sky by joining up the stars, although not perfectly straight, the line equates to the cleavage planes in slate, which are not flat either! The direction of applied force is rather academic, as a cleavage plane is rather dictated for us!

As to the sound of slate. MMM! I've done a calculation, for a typical plinth size and shape [432mm x 343mm x 25mm]. It looks like the fundamental frequency is at 514Hz, which is above the critical frequency of 463Hz. So all the resonances are above the critical region, meaning the damping controlled zone, where it has very little damping!

So I expect the bass region to be well controlled (no exaggerated bass from resonances, but it might sound bass light compared to wooden plinths). I expect a lot of resonances in the 1kHz to 15kHz range, and a big area of grunge around 500Hz - 1kHz, where the slate is transparent to sound. It might depend on what you place the slate plinth on, and what 'legs' you use. Isolation, rather than mechanical grounding is the way to go if bothered by seismic problems in this case.
'Ring' any bells? hats off


The Kenwood I was aware of, one of the very few to have a composite base structure.


Dernière édition par Bryan le Mer 17 Fév - 11:16 (2010); édité 6 fois
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MessagePosté le: Mar 16 Fév - 16:57 (2010)    Sujet du message: Slate/Ardoise Répondre en citant

Gentlemen,

For reasons of readability, I have split the messages related to slate from the original thread and created a new thread.

bow


hats off
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MessagePosté le: Mar 16 Fév - 17:35 (2010)    Sujet du message: Slate/Ardoise Répondre en citant

Lew,
you might like a look at this:



[image borrowed from ebay without owners permission, who probably didn't get permission to copy it either!]

It's data from Kenwood's ceramic platter mat, TS-10.

Look at the graphs, it confirms what I have been trying to say about materials. Look at the glass graph, low vibrations in the bass region, but significant in the >500Hz range, like slate. The rubber looks OK because it has damping, and the Q is very low, meaning any resonance peaks are spread out.
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