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Bryan
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MessagePosté le: Lun 4 Oct - 17:47 (2010)    Sujet du message: Damping factors Répondre en citant

maco a écrit:
Bryan a écrit:
François a écrit:
Bryan a écrit:
I know which one I'm building! #violon# fête


You may be wanting to wait and see how "composite" materials behave Question Wink



you are quite right, of course, but it's the thought of all those equations, which will be much more complicated with two or more materials to cope with. Crying or Very sad
But already, it shows (if the calculations are correct) why slate is a little better than plywood, but nowhere near as good as polyester resin! #violon# #violon# #violon# fête Cool


Hi Bryan,

That's brilliant ! Okay  The Polyester resin really sets the mark! Shocked  What parameters do you need to calculate the Bamboo ply ?(thickness 80mm, 40x46.5cm ) Smile  

hats off
Hi Maco,

I need Young's modulus, Poisson ratio (or shear modulus) damping factor, density, and dimensions only.

So really, only Young's modulus missing. I would guess Poisson ratio is about 0.4.
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MessagePosté le: Lun 4 Oct - 17:47 (2010)    Sujet du message: Publicité

PublicitéSupprimer les publicités ?
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MessagePosté le: Lun 4 Oct - 18:56 (2010)    Sujet du message: Damping factors Répondre en citant

Bryan,

Don't know wether this information can be useful for the calculation for Bamboo ply :

Hardness: 4,0 kg/mm² (Brinell)
;
Shrink/swell: 0,14% per 1% change in moisture content
Equilibrium MC: 10% at 20 ºC and 65% Rel. Air Humidity
8% at 20 ºC and 50% Rel. Air Humidity
Density: 700 kg/ m³;
Glue: D3 water resistant
Fire resistance: EN 13501-1: D-s1 (40mm thickness)
Emission formaldehyde: <0,124 mg/m³ (E1 norm)
Elastic modulus : ca. 4300 N/mm2 (40mm).

Guess the elastic modulus is another term for the Young's modulus Question

The plinth (see BambooLenco thread) measures 400x460x80 mm

More info here : http://www.moso-bamboo.com/files/EN_MOSO Solid panel.pdf

bow hats off
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MessagePosté le: Mar 5 Oct - 18:34 (2010)    Sujet du message: Damping factors Répondre en citant

using this information and the value of the damping factor I measured on a similar panel, I arrived at the following:

this is for 80mm thick plinth:


© Bryan 2010
and for a 40mm thick plinth:


© Bryan 2010

The 40mm thick plinth looks a little better, but there isn't much in it.

How have you connected the two layers together?
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MessagePosté le: Mar 5 Oct - 19:06 (2010)    Sujet du message: Damping factors Répondre en citant

Bryan a écrit:
using this information and the value of the damping factor I measured on a similar panel, I arrived at the following:

this is for 80mm thick plinth:


© Bryan 2010
and for a 40mm thick plinth:


© Bryan 2010

The 40mm thick plinth looks a little better, but there isn't much in it.

How have you connected the two layers together?
Looks like an acceptable graph Exclamation Smile
For the time being the 2 layers are not bonded at all, just piled up. The surfaces are so plane that the barely slip on one another. Before bonding I just wanted to hear the difference between one and two layers. Your calculation seems to give the answer Okay . What I do not know how to interpret in the first graph is the opening at 10Khz Question Does it means that high frequency is being abnormally damped ? Anyway I prefer the second graph with one layer only. Leaves me a spare plinth for another project Laughing . Also taking note of the 800Hz hump instead of the 400Hz in the first graph. How can this be explained?

Many thanks for taking time and checking out !
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MessagePosté le: Mar 5 Oct - 21:40 (2010)    Sujet du message: Damping factors Répondre en citant

for the 40mm thickness, both the fundamental resonance and critical frequencies are about 600Hz, whereas, for the 80mm thick panel, the fundamental frequency doubles to 1200Hz, while the critical frequency halves to 300Hz.

The important difference, I believe, is not the above, but the losses from 20 to about 1kHz. The 80mm thick plinth has 15 - 20 dB losses, whereas the 40mm has 20 -25dB losses over a wider range, so is better, in this respect. Remember, for sound pressure, 20dB is 100 times. I would suggest 20dB down is a minimum.

HTH Wink

love what you have done to the tone arm, how did you make the piece which holds the cartridge and fits into the tube? IMHO, the L75 arm is let down by the headshell,  aesthetically.
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MessagePosté le: Mar 5 Oct - 23:03 (2010)    Sujet du message: Damping factors Répondre en citant

Bryan a écrit:
... how did you make the piece which holds the cartridge and fits into the tube? IMHO, the L75 arm is let down by the headshell,  aesthetically.
Thanks bow and I agree: the old Headshell is a disgrace (aesthically). The carbon wand is also a good replacement, optically and being longer it needs to be stiffer, which it is. The whole behaves less wobbly too...

The carbon tube has 8mm inside diameter. To make the headshell fixation I used a 6cm long aluminium 8mm rod and manually cut and filed it as required. The rod snugly fits the tube and can additionally be secured with a M3 screw to the armwand.
The piece which holds the cartridge is a non-magnetic metallic round piece recycled from a broken Lenco L78 dustcover hinge . This is then fixed onto the aluminium rod's end with one M4 screw. The beauty of it is how easy adjusting the cart is if you only have to fix it with a single screw. Well nothing new, Clearaudio uses a similar trick..

When the finish will be neat enough, I will post pictures and explanations in the BambooLenco thread.

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MessagePosté le: Mer 6 Oct - 10:55 (2010)    Sujet du message: Damping factors Répondre en citant

Hi Bryan, (its me again ...  Mr. Green )

I have found that the (trial) system of my tonearmbase is not so bad. To build the base I used a 12cm diameter 2mm carbon sheet, layered and bonded with 5 CDs Evil or Very Mad below. The subjective finding is that this combination gives good response and damps quite good (knocking test). The upper layer being carbon 2mm sheet it is also stiff as a whole. So far I am considering making a final version of such a tonearmbase. What may be of interest in this discussion are the properties of the CD or DVD material. It consists of Polycarbonate layers with small film of aluminium for the reflective part. Here are the specs for Polycarbonate I found on Wikipedia :



Finally smoke ,  would CDs be useful for turntablists Question
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MessagePosté le: Mer 6 Oct - 11:03 (2010)    Sujet du message: Damping factors Répondre en citant

maco a écrit:
Finally smoke ,  would CDs be useful for turntablists Question

Yes, put two of them under the mat to fill the hole of the platter Wink
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MessagePosté le: Mer 6 Oct - 12:09 (2010)    Sujet du message: Damping factors Répondre en citant

François a écrit:
maco a écrit:
Finally smoke ,  would CDs be useful for turntablists Question

Yes, put two of them under the mat to fill the hole of the platter Wink
best thing I have found for cd's is as a coaster under cups/glasses, or under a table leg to level the table!!

Thanks for the info, maco, it is very similar to what I have seen. What is missing (as it is in most cases) is the damping factor, which is why I spend some time measuring them all. I have a 300mm video disc which I bought to do some work with bias adjustments with. I measured the damping factor to be 0.033 suspended in air, and 0.079 when put on my platter mat.

I don't know yet about composite structures, like sandwich layers of different materials. Carbon fibre/ resin is extremely stiff, similar to steel. On its own it is poor a material for our needs, but as a facing in a sandwich, it might be very good. I have been surprised how good materials, which, on their own are poor (acoustically) but in combination with other equally poor materials, provide good materials as sandwiches. Aluminium/polyalkane/aluminium and Al/mdf/Al have both given good damping factors, the former is François' table tennis sample, and the other is a board to be sold for Linn turntable replacement bits.

I'm hoping to complete the equations which calculate responses for 2,3 and 5 layers of different materials soon, so I'll post as soon as. I'll also post all the calculations and data on a new web site, a sister site to my usual one.
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MessagePosté le: Jeu 7 Oct - 13:20 (2010)    Sujet du message: Damping factors Répondre en citant

I think I have managed to expand ( Twisted Evil ) the calculations to include two layer composites.

Having only looked at one, aluminium over polyester, its looks as though 25mm of polyester is equivalent to 2mm aluminium over 21mm polyester. Both goodness factors are the same (for the same sized plinth, .35m x 0.4m), and losses from 20 to 1000Hz are between 34 and 43dB for both, an excellent figure.

It looks as though François' intuition is right , again.   bow
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MessagePosté le: Jeu 7 Oct - 13:34 (2010)    Sujet du message: Damping factors Répondre en citant

Bryan a écrit:
It looks as though François' intuition is right , again.   bow

Please, don't make me blush Embarassed Wink

bow



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MessagePosté le: Ven 8 Oct - 00:31 (2010)    Sujet du message: Damping factors Répondre en citant

hey, credit where credit's due  Wink (as they use to say in my bank!!!).

I think I have the next stage done (sandwich, three layers, top and bottom the same)

For 2mm aluminium, 8mm polyester, 2mm aluminium, goodness 2354, for a .34m x .4m panel.
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MessagePosté le: Ven 8 Oct - 06:43 (2010)    Sujet du message: Damping factors Répondre en citant

Bryan a écrit:
hey, credit where credit's due  Wink (as they use to say in my bank!!!).

So I'd be more than happy to share it with Rap Wink
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MessagePosté le: Mar 8 Fév - 12:35 (2011)    Sujet du message: Damping factors Répondre en citant

Hello  Bryan 


It seems that Acetal Sheet called Delrin is a very good stuff to build a plinth
Do know it  ? 


http://www.tapplastics.com/shop/product.php?pid=337


and here is a thread on lenco heaven:


http://www.lencoheaven.net/forum/index.php?topic=2150.msg29712#msg29712


and here


http://www.lencoheaven.net/forum/index.php?topic=2352.15



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MessagePosté le: Mer 9 Fév - 13:23 (2011)    Sujet du message: Damping factors Répondre en citant

yes, I have tested Delrin for damping factor, and it is poor. The figure I obtained was 0.013, worse that slate!

I am afraid you have been too quick to accept others testimony. Delrin is very poor at damping, yet another urban myth.

Have a look on my web site, under damping factor, http://www.lencoheaven.net/forum/index.php?topic=2352.15

and see what is good, and not so good.


I used to be a member of Lenco heaven, but found that they were very blinkered in their thinking, not willing to accept anything that was contrary to their beliefs.

It is one thing to build something and be self critical, as François is, as are others on this forum, but other forums are littered with people who believe what they have built is wonderful, so that others follow blindly, and urban myths start.

For me, I need measurement to show a good product, or which direction should be taken. Only then is progress made. Wink
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