Hi Carlo,
I hadn't considered the ease of machining of the different materials. The acrylic was quite a nice material to work with. I did show slight judder marks after being cut with the router but these sanded out with a couple of passes with coarse paper. It might be possible to flame polish delrin or nylon in a similar fashion to that often used to finish acrylic. I've not found this method as good as hand finishing but it's a lot quicker. Personally I put up with a material being a pig to work if it sounds better.
The delrin I gave the impedance for was indeed the black version. Black nylon 6/6 should also make a very good platter having a Z of 3.15, natural nylon 6/6 has a Z of 2.9. Black nylon also has much better damping than natural. This would probably put nylon in the top 3 or 4 materials for platters, depending on whether a platter of record vinyl was feasible.
I'm very happy with the performance of my solid acrylic platter and I am not planning on changing it. It is still interesting to keep up the investigation into alternative materials or combinations of materials.
Hi Walter,
I don't have any specs for shellac but guess it would have similar properties to delrin. Depending on how good the damping is it could make a good mat. The choice of glue will have an influence as well.
I have heard very good things about the use of foamed vinyl as the material for platter mats. I've seen it on ebay in 5 and 10mm sheets.
Niffy
I hadn't considered the ease of machining of the different materials. The acrylic was quite a nice material to work with. I did show slight judder marks after being cut with the router but these sanded out with a couple of passes with coarse paper. It might be possible to flame polish delrin or nylon in a similar fashion to that often used to finish acrylic. I've not found this method as good as hand finishing but it's a lot quicker. Personally I put up with a material being a pig to work if it sounds better.
The delrin I gave the impedance for was indeed the black version. Black nylon 6/6 should also make a very good platter having a Z of 3.15, natural nylon 6/6 has a Z of 2.9. Black nylon also has much better damping than natural. This would probably put nylon in the top 3 or 4 materials for platters, depending on whether a platter of record vinyl was feasible.
I'm very happy with the performance of my solid acrylic platter and I am not planning on changing it. It is still interesting to keep up the investigation into alternative materials or combinations of materials.
Hi Walter,
I don't have any specs for shellac but guess it would have similar properties to delrin. Depending on how good the damping is it could make a good mat. The choice of glue will have an influence as well.
I have heard very good things about the use of foamed vinyl as the material for platter mats. I've seen it on ebay in 5 and 10mm sheets.
Niffy
I have the feeling that shellac may not be good material for platter mat or platter. I believe a good platter material should be combination of aluminum and stainless steel. For mat, I used carbon fiber and am using a combination of carbon fiber and brass sheet. Both are good mats. Actually, it is hard to say which material is good because it depends on very much personal preference. Usually, a good designed table needs no mat at all such as my SME 20. Mat is used to alter sound to fit your personal preference.
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Haven't been very active on this thread (or pretty much at all lately), so let me start by thanking you all for the great contributions throughout the thread. I have yet to embark on the road to a linear tonearm (still scares me), but perhaps I can share my insight as to some platter materials.
I chose to go with a split platter, bottom massive platter of 6082 aluminium, and top light platter of white POM (Delrin). Still experimenting with coupling between the platters, but a hard coupling (bronze + ceramics) seems to work best in my application.
I can attest to the "brightness" effect of a "naked" aluminium platter. This might also have something to do with the fact that I had it anodized, which introduced a hard, albeit thin, layer on the actual platter.
But to me, the combination of the mass of the aluminium and some of the inherent damping along with the qualities of Delrin (to which the record couples directly) seem to bring out the best combination so far.
Delrin has been, in our experience, easy to machine. Could be a combination of tools and other conditions at the machine shop I am using. However, I can attest to the difficulty obtaining a satisfactory finish. In my application, again, the benefits far outweigh all these difficulties, which is why we went with Delrin, as opposed to acrylic.
I would have liked to know beforehand what @hottattoo rightfully pointed out about the machining of materials in multiple stages. We learned the hard way (losing time and materials) that materials like to be "relaxed" in between machining passes. For quite some time we couldn't figure out why would platters develop warps, even if not very noticeable. Having the procedure split to "rough machining" and "final machining" with some time to rest between has solved a number of these issues.
Of course, the actual design of a split platter does introduce an even greater risk of platter runout, but I've chosen to live with such a risk as opposed to the benefits it brings. I still am shocked that so many commercial turntables have, what is to us, unacceptable levels of platter runout.
I chose to go with a split platter, bottom massive platter of 6082 aluminium, and top light platter of white POM (Delrin). Still experimenting with coupling between the platters, but a hard coupling (bronze + ceramics) seems to work best in my application.
I can attest to the "brightness" effect of a "naked" aluminium platter. This might also have something to do with the fact that I had it anodized, which introduced a hard, albeit thin, layer on the actual platter.
But to me, the combination of the mass of the aluminium and some of the inherent damping along with the qualities of Delrin (to which the record couples directly) seem to bring out the best combination so far.
Delrin has been, in our experience, easy to machine. Could be a combination of tools and other conditions at the machine shop I am using. However, I can attest to the difficulty obtaining a satisfactory finish. In my application, again, the benefits far outweigh all these difficulties, which is why we went with Delrin, as opposed to acrylic.
I would have liked to know beforehand what @hottattoo rightfully pointed out about the machining of materials in multiple stages. We learned the hard way (losing time and materials) that materials like to be "relaxed" in between machining passes. For quite some time we couldn't figure out why would platters develop warps, even if not very noticeable. Having the procedure split to "rough machining" and "final machining" with some time to rest between has solved a number of these issues.
Of course, the actual design of a split platter does introduce an even greater risk of platter runout, but I've chosen to live with such a risk as opposed to the benefits it brings. I still am shocked that so many commercial turntables have, what is to us, unacceptable levels of platter runout.
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I have to say, at the time my project got started, I was limited by the choice of materials. Local suppliers started offering some materials after I had made repetitive queries - online ordering is not an option for such sizes. At some point, even the design of the TT was somewhat influenced by available materials.
There was black Delrin (I hesitate to use that name as the POM I am using most certainly wasn't manufactured by Dupont) but I was not sure (still aren't) if that black variant which was on offer is graphite-loaded as Carlo suggests. The color white in my case has the added benefit of color matching with the clear anodized aluminium and beech/maple base which is crucial if that monstrosity is to survive in the living room with the wife around.
I may yet experiment with black POM, but not in the immediate future - that supplier requires me to order a larger quantity and we end up with a bunch of unused POM which we had paid for.
As for the final platter dimensions... lower platter is 320mm x 65mm (aluminium) and the top platter is 320mm x 15mm (POM) - hope this helps.
Who here has the ability to machine a platter out of bullet proof glass for me which is basically plexiglass on steroids I have it in 1”1/4” thick
like to have three of them machine for me
Please email me. I would give this person some of this if they would like some for themselves
carlthess@icloud.com
like to have three of them machine for me
Please email me. I would give this person some of this if they would like some for themselves
carlthess@icloud.com
It wouldn,t be a dead as acrylic at the same thickness.
If anything it would very easily transmit bearing issues right thru to the stylus.
Better it was 3 layers of glass with a soft glue sandwidwich between layers than solid Glass.
Now if was bulletproof kevlar or the very dense fiberglass that is also used as bulletproof material, you might have something worth considering, but not glass.
Regards
David
If anything it would very easily transmit bearing issues right thru to the stylus.
Better it was 3 layers of glass with a soft glue sandwidwich between layers than solid Glass.
Now if was bulletproof kevlar or the very dense fiberglass that is also used as bulletproof material, you might have something worth considering, but not glass.
Regards
David
It’s the real deal bullet proof glass. My brother bought all the items from a bank that closed down. All the safes and all the
B/P glass that was for all the bank tellers
The last pic is from a full metal jacket 308 shoot from 10 feet
As you can see it did not go though it. Lol
This stuff is 1.25” thick
Hi carlthess40,
It doesn't really answer the question as to whether the bullet proof glass is a plastic or silicate. I can see no evidence of lamination which would suggest that it is a plastic. The fracture pattern is more like I would expect from a plastic. Although I have performed quite a bit of materials testing I have never resorted to the use of small calibre artillery, so I might be a bit hazy as to the type of fracture pattern to expect.
If it is plastic/plexiglass it will probably make a fine platter. If it is an actual glass then it will need some form of platter mat or it could be used as the base layer in a two part platter.
Either type of material could be successfully incorporated into the plinth of a turntable.
Niffy
It doesn't really answer the question as to whether the bullet proof glass is a plastic or silicate. I can see no evidence of lamination which would suggest that it is a plastic. The fracture pattern is more like I would expect from a plastic. Although I have performed quite a bit of materials testing I have never resorted to the use of small calibre artillery, so I might be a bit hazy as to the type of fracture pattern to expect.
If it is plastic/plexiglass it will probably make a fine platter. If it is an actual glass then it will need some form of platter mat or it could be used as the base layer in a two part platter.
Either type of material could be successfully incorporated into the plinth of a turntable.
Niffy
Hi all
sorry to go back to basics, but I would like to understand better this argument, to take advantage of your results. When saying - this sounds better than that - maybe it would be necessary to specify what we want to achieve, because there are two problems that seem completely different, to me
1 - the platter must not transmit the noise of the bearing and/or motor to the disc. For this it is used
A a completely isolated motor - B a dead silent bearing - C a platter with high impedance to resonances - D a soft and not so dense mat (felt - foam - etc)
2 - the platter must absorb the resonances induced by the tracing on the disc itself. For this it is used
X a medium to heavy density elastic mat (+ clamp) - Y a rigid mat perfectly adherent to the plate, or no mat at all (again + clamp)
1 - D solution is the most beloved by some manufacturers because it masks defects in A B C, but also by many audiophiles who like a richer sound. (there was an entire school). Not my case.
A + B seem indispensable, but being almost unknown on this earth the condition C can be extremely useful. The problem is the material (or materials) of the platter, but the bearing to platter joint plays even a bigger role.
2 - X solution is the most commonly used, but it's a difficult compromise (from no absorption to free resonances, as in D) - Y is difficult to obtain, because the disk must become one thing with the platter itself (just a non perfect contact brings troubles).
When the platter transmits noises from the bearing to the disc the Y is clearly to be avoided.
My TT project stopped at B (decent bearings, but not silent), some results obtained by attaching the bearing only to the subplatter (also used to register the wobble) and various tests on how to connect the sub to the platter.
carlo
to simplify I deliberately neglected the noises coming directly from the main bearing to the TA base.
sorry to go back to basics, but I would like to understand better this argument, to take advantage of your results. When saying - this sounds better than that - maybe it would be necessary to specify what we want to achieve, because there are two problems that seem completely different, to me
1 - the platter must not transmit the noise of the bearing and/or motor to the disc. For this it is used
A a completely isolated motor - B a dead silent bearing - C a platter with high impedance to resonances - D a soft and not so dense mat (felt - foam - etc)
2 - the platter must absorb the resonances induced by the tracing on the disc itself. For this it is used
X a medium to heavy density elastic mat (+ clamp) - Y a rigid mat perfectly adherent to the plate, or no mat at all (again + clamp)
1 - D solution is the most beloved by some manufacturers because it masks defects in A B C, but also by many audiophiles who like a richer sound. (there was an entire school). Not my case.
A + B seem indispensable, but being almost unknown on this earth the condition C can be extremely useful. The problem is the material (or materials) of the platter, but the bearing to platter joint plays even a bigger role.
2 - X solution is the most commonly used, but it's a difficult compromise (from no absorption to free resonances, as in D) - Y is difficult to obtain, because the disk must become one thing with the platter itself (just a non perfect contact brings troubles).
When the platter transmits noises from the bearing to the disc the Y is clearly to be avoided.
My TT project stopped at B (decent bearings, but not silent), some results obtained by attaching the bearing only to the subplatter (also used to register the wobble) and various tests on how to connect the sub to the platter.
carlo
to simplify I deliberately neglected the noises coming directly from the main bearing to the TA base.
Hi Carlo,
To me the primary role of the platter is to allow the energy caused by the tracing of the groove to propagate away from the stylus and to prevent any of it from then returning to the stylus.
I don't think that the platter should have acting as a barrier between the bearing/motor and stylus as its main responsibility. A major point of my sleeveless bearing was to reduce bearing noise as far as possible. I cannot hear any noise at all from the bearing when using my mechanics stethoscope. (I initially thought I could hear some. Turned out that I could still hear it when the platter wasn't rotating or even fitted. It was a combination of the blood moving through my hand and traffic noise, not the bearing at all. ) Likewise I cannot hear any motor noise breakthrough south of the motor mounts. Motor isolation is even more important to me than most as my motor is mounted on the sub-chassis. I chose to tackle motor and bearing noise at source rather than trying to deal with it further down the chain.
The predominant type of vibration caused by the stylus/groove interaction is compression (sound) waves. By impedance matching the platter to the record the energy of this stylus/groove interaction can propagate away from the stylus with minimal hindrance. Having a material that attenuates the compression waves as much as possible is of course desirable.
As the compression waves move through the platter they induce bending waves. These form a pattern of nodes and antinodes that change depending on the frequency and position of the stylus. The best way to visualise how these occur is by looking at chladni plates.
YouTube
This is an over simplified example as only a single note is played and forms stationery nodes. Real music would produce more complex patterns that constantly change. The simplest pattern of nodes is where they form a cross with adjacent antinodes being out of phase. Of course chladni plates are designed to resonate in order to demonstrate the effect. Making the platter out of a material with better damping and by simply making the platter thicker can prevent the more complex patterns from forming and greatly reduce the formation of the simplest patterns. Ideally we want to prevent any patterns from forming as these represent resonances. (Increasing the thickness of the platter also means that the compression waves have to travel through a greater mass of material before they can be reflected back, reducing their amplitude). In addition to making the platter thicker making it out of a couple of distinct layers should increase damping and prevent the formation of resonances.
The plinth and part of the sub-chassis of my deck are made of sandwiches of aluminium and acrylic. The plinth is 20mm acrylic with 5mm aluminium skins. By itself the aluminium rang like a bell when struck. It also readily transmitted sound waves. The acrylic was quite dead and was inefficient at transmitting sound waves. Just gluing one piece of the aluminium to the acrylic massively deadened the whole thing making it much better than either material was in isolation. The addition of the aluminium didn't appear to effect the transmission of sound through the acrylic side. The addition of the second skin improved the deadness of the structure but substantial increased its ability to transmit sound waves. Please note that I am differentiating between bending and compression (sound) waves as they behave differently and need to be treated differently. Possibly the best solution would be a thick layer of aluminum with a thick layer of acrylic (or similar plastic) bonded to it. As proposed by AVWERK, though I might be tempted to go for less dissimilar thicknesses.
A reasonably thick layer of acrylic will by itself offer substantial damping and resistant to resonance. Whether there is a worthwhile improvement in adding an extra layer would require further investigation. I suspect that it will be marginally beneficial.
Apart from having the best impedance match to record vinyl acrylic does have a couple more things in its favor. It is considerably cheaper than all of the other materials that have been discussed here, it is also readily available in a wide range of thicknesses of up to 100mm. It is probably the easiest to work as well. I think a lot of people are put off acrylic as it isn't seen as high tech enough and can appear visually tacky.
Niffy
To me the primary role of the platter is to allow the energy caused by the tracing of the groove to propagate away from the stylus and to prevent any of it from then returning to the stylus.
I don't think that the platter should have acting as a barrier between the bearing/motor and stylus as its main responsibility. A major point of my sleeveless bearing was to reduce bearing noise as far as possible. I cannot hear any noise at all from the bearing when using my mechanics stethoscope. (I initially thought I could hear some. Turned out that I could still hear it when the platter wasn't rotating or even fitted. It was a combination of the blood moving through my hand and traffic noise, not the bearing at all. ) Likewise I cannot hear any motor noise breakthrough south of the motor mounts. Motor isolation is even more important to me than most as my motor is mounted on the sub-chassis. I chose to tackle motor and bearing noise at source rather than trying to deal with it further down the chain.
The predominant type of vibration caused by the stylus/groove interaction is compression (sound) waves. By impedance matching the platter to the record the energy of this stylus/groove interaction can propagate away from the stylus with minimal hindrance. Having a material that attenuates the compression waves as much as possible is of course desirable.
As the compression waves move through the platter they induce bending waves. These form a pattern of nodes and antinodes that change depending on the frequency and position of the stylus. The best way to visualise how these occur is by looking at chladni plates.
YouTube
This is an over simplified example as only a single note is played and forms stationery nodes. Real music would produce more complex patterns that constantly change. The simplest pattern of nodes is where they form a cross with adjacent antinodes being out of phase. Of course chladni plates are designed to resonate in order to demonstrate the effect. Making the platter out of a material with better damping and by simply making the platter thicker can prevent the more complex patterns from forming and greatly reduce the formation of the simplest patterns. Ideally we want to prevent any patterns from forming as these represent resonances. (Increasing the thickness of the platter also means that the compression waves have to travel through a greater mass of material before they can be reflected back, reducing their amplitude). In addition to making the platter thicker making it out of a couple of distinct layers should increase damping and prevent the formation of resonances.
The plinth and part of the sub-chassis of my deck are made of sandwiches of aluminium and acrylic. The plinth is 20mm acrylic with 5mm aluminium skins. By itself the aluminium rang like a bell when struck. It also readily transmitted sound waves. The acrylic was quite dead and was inefficient at transmitting sound waves. Just gluing one piece of the aluminium to the acrylic massively deadened the whole thing making it much better than either material was in isolation. The addition of the aluminium didn't appear to effect the transmission of sound through the acrylic side. The addition of the second skin improved the deadness of the structure but substantial increased its ability to transmit sound waves. Please note that I am differentiating between bending and compression (sound) waves as they behave differently and need to be treated differently. Possibly the best solution would be a thick layer of aluminum with a thick layer of acrylic (or similar plastic) bonded to it. As proposed by AVWERK, though I might be tempted to go for less dissimilar thicknesses.
A reasonably thick layer of acrylic will by itself offer substantial damping and resistant to resonance. Whether there is a worthwhile improvement in adding an extra layer would require further investigation. I suspect that it will be marginally beneficial.
Apart from having the best impedance match to record vinyl acrylic does have a couple more things in its favor. It is considerably cheaper than all of the other materials that have been discussed here, it is also readily available in a wide range of thicknesses of up to 100mm. It is probably the easiest to work as well. I think a lot of people are put off acrylic as it isn't seen as high tech enough and can appear visually tacky.
Niffy
Niffy, to rely on your knowledge and experience is not just a privilege, often brings decisive advantages.
What you say about the vibrations induced on the disc is absolutely relevant: simply trying mats of different materials is enough to get the clear proof of that.
Test after test convinced me too that the only way to handle the problem is to make the disc solidary (not so easy) with a platter capable to absorb those vibrations, and I think I will go to plexy for the advantages you describe, and that somehow I know.
However, this aspect needs an indispensable premise: an absolutely dead silent turntable.
Several steps behind to this achievement I have to make first a main bearing that behaves correctly (some sintered bronze bushing bought look promising) and to be able to absorb the residual noise before reaching the platter.
I'm starting from where I gave up: a traditional (?) inverse bearing, but now increasing the bearing to platter separation through a PVC subplatter + a small air gap. (attachment)
Back to topic: Lil Casey mk2 parts almost made. (attachment)
Now begins a very careful bonding - assembly, since the pen-tips must be perfectly aligned, and the rail - parallelogram system too. That means time, and other templates (again!).
To be continued
ciao carlo
What you say about the vibrations induced on the disc is absolutely relevant: simply trying mats of different materials is enough to get the clear proof of that.
Test after test convinced me too that the only way to handle the problem is to make the disc solidary (not so easy) with a platter capable to absorb those vibrations, and I think I will go to plexy for the advantages you describe, and that somehow I know.
However, this aspect needs an indispensable premise: an absolutely dead silent turntable.
Several steps behind to this achievement I have to make first a main bearing that behaves correctly (some sintered bronze bushing bought look promising) and to be able to absorb the residual noise before reaching the platter.
I'm starting from where I gave up: a traditional (?) inverse bearing, but now increasing the bearing to platter separation through a PVC subplatter + a small air gap. (attachment)
Back to topic: Lil Casey mk2 parts almost made. (attachment)
Now begins a very careful bonding - assembly, since the pen-tips must be perfectly aligned, and the rail - parallelogram system too. That means time, and other templates (again!).
To be continued
ciao carlo
Attachments
Further musings on platter materials
Earlier I suggested the use of a couple of similar layers or a gradient of layers to absorb compression waves. In my last post I introduced the idea of using dissimilar layers (acrylic and aluminium) to damp bending waves within the platter. I think that the latter has greater potential. If making a very thick (80mm+) and heavy platter I would suggest making the layers of a similar thickness. For lighter platters I would suggest making the acrylic somewhere in the range of twice as thick as the aluminium. My reason for this is that the acrylic is the platter and is the thing that is in direct contact with the record. Having a thick layer of acrylic will absorb as much of the compression waves as possible. The aluminium layer is there to damp the bending waves within the acrylic.
The alternative option is to have a thick layer of aluminium with a thinner layer of acrylic on top. In this case the acrylic is acting more like a thick platter mat trying to impedance match the record to the platter below. Having a thinner layer of acrylic will result in greater reflection from the acrylic/aluminium boundary. Of course the platter with the thicker layer of aluminium will weigh a lot more than the platter with the thicker layer of acrylic assuming the same overall thickness. This will require a more substantial bearing and the associated noise penalty.
My platter is a solid piece of acrylic 40mm thick. If I wanted to make a two layer aluminium /acrylic platter of the same mass it would probably be something like 20mm of acrylic with 8mm of aluminium or 15mm of acrylic with 10mm of aluminium. Both of these options would result in much greater reflection than I currently have from the underside of the platter. Would a thinner two part platter actually offer greater rigidity or damping, probably not. At these sort of dimensions I feel that a single piece, single material platter will be superior. Another benefit to me is that the 40mm acrylic platter would have a lower centre of mass. This helps to keep my sleeveless bearing stable.
If we were to be comparing an 80mm single piece acrylic platter to 40mm acrylic with 15mm of aluminium (same mass) I think the differences would start to swing more towards the two piece platter. I think that once you get up to this sort of mass and thickness the difference in sound is going to be quite subtle which is why I said in the previous post that the benefits will be marginal.
I have been thinking mainly about using acrylic and aluminium. Of course the plastic could be one of many different types. Delrin or PVC being obvious alternatives. The aluminium could be replaced by steel, magnesium, corian or a laminated combination of materials.
Unfortunately we cannot easily determine which material or combination of materials is going to sound the best without actually building platters and playing records. We can however narrow the range of options to those most likely to work well.
Niffy
Earlier I suggested the use of a couple of similar layers or a gradient of layers to absorb compression waves. In my last post I introduced the idea of using dissimilar layers (acrylic and aluminium) to damp bending waves within the platter. I think that the latter has greater potential. If making a very thick (80mm+) and heavy platter I would suggest making the layers of a similar thickness. For lighter platters I would suggest making the acrylic somewhere in the range of twice as thick as the aluminium. My reason for this is that the acrylic is the platter and is the thing that is in direct contact with the record. Having a thick layer of acrylic will absorb as much of the compression waves as possible. The aluminium layer is there to damp the bending waves within the acrylic.
The alternative option is to have a thick layer of aluminium with a thinner layer of acrylic on top. In this case the acrylic is acting more like a thick platter mat trying to impedance match the record to the platter below. Having a thinner layer of acrylic will result in greater reflection from the acrylic/aluminium boundary. Of course the platter with the thicker layer of aluminium will weigh a lot more than the platter with the thicker layer of acrylic assuming the same overall thickness. This will require a more substantial bearing and the associated noise penalty.
My platter is a solid piece of acrylic 40mm thick. If I wanted to make a two layer aluminium /acrylic platter of the same mass it would probably be something like 20mm of acrylic with 8mm of aluminium or 15mm of acrylic with 10mm of aluminium. Both of these options would result in much greater reflection than I currently have from the underside of the platter. Would a thinner two part platter actually offer greater rigidity or damping, probably not. At these sort of dimensions I feel that a single piece, single material platter will be superior. Another benefit to me is that the 40mm acrylic platter would have a lower centre of mass. This helps to keep my sleeveless bearing stable.
If we were to be comparing an 80mm single piece acrylic platter to 40mm acrylic with 15mm of aluminium (same mass) I think the differences would start to swing more towards the two piece platter. I think that once you get up to this sort of mass and thickness the difference in sound is going to be quite subtle which is why I said in the previous post that the benefits will be marginal.
I have been thinking mainly about using acrylic and aluminium. Of course the plastic could be one of many different types. Delrin or PVC being obvious alternatives. The aluminium could be replaced by steel, magnesium, corian or a laminated combination of materials.
Unfortunately we cannot easily determine which material or combination of materials is going to sound the best without actually building platters and playing records. We can however narrow the range of options to those most likely to work well.
Niffy
Simple question for all:
I’ve read the posts in this thread and also discussions in many forums across the internet about the choice of platter materials and coupling the disk to the platter. I get the concept that it’s desirable for the platter and mat (or no mat) to be non-resonant and have some inherent damping characteristics, and I kind-of get the concept of matching the mechanical impedance of the platter material to the mechanical impedance of the record vinyl. A ubiquitous ‘solution’ for this has been a record clamp on the spindle and, less often, a perimeter clamp. But do these really couple the record groove area between the label and the outer bead to the platter and provide the full benefit of siphoning away unwanted vibrations? In general, most all of the platters I see which use/capitalize on the damping and mechanical impedance properties of ‘special characteristic’ materials are totally flat. I’m not referring to runout or wobble here. Too, rubber mats that come as OEM on many vintage 12-inch turntable platters have a raised bead around the perimeter and at the label area to intentionally prevent contact with the groove area on the underside of the record.
To couple the record groove area to the platter and reap the theoretical benefits of specialized materials and/or construction methods such as layering/lamination, solid platters should have a recess machined in them at the 12-inch perimeter under the LP record bead, and at the center under the record label. Furthermore, to truly couple the record groove area to the platter, a vacuum hold-down system would be in order. Otherwise, a perfectly flat LP on a perfectly flat solid surface has an air gap between the record groove area and the platter. It will act as a drum. I’ve not seen this issue being addressed.
Ray K
I’ve read the posts in this thread and also discussions in many forums across the internet about the choice of platter materials and coupling the disk to the platter. I get the concept that it’s desirable for the platter and mat (or no mat) to be non-resonant and have some inherent damping characteristics, and I kind-of get the concept of matching the mechanical impedance of the platter material to the mechanical impedance of the record vinyl. A ubiquitous ‘solution’ for this has been a record clamp on the spindle and, less often, a perimeter clamp. But do these really couple the record groove area between the label and the outer bead to the platter and provide the full benefit of siphoning away unwanted vibrations? In general, most all of the platters I see which use/capitalize on the damping and mechanical impedance properties of ‘special characteristic’ materials are totally flat. I’m not referring to runout or wobble here. Too, rubber mats that come as OEM on many vintage 12-inch turntable platters have a raised bead around the perimeter and at the label area to intentionally prevent contact with the groove area on the underside of the record.
To couple the record groove area to the platter and reap the theoretical benefits of specialized materials and/or construction methods such as layering/lamination, solid platters should have a recess machined in them at the 12-inch perimeter under the LP record bead, and at the center under the record label. Furthermore, to truly couple the record groove area to the platter, a vacuum hold-down system would be in order. Otherwise, a perfectly flat LP on a perfectly flat solid surface has an air gap between the record groove area and the platter. It will act as a drum. I’ve not seen this issue being addressed.
Ray K
You are absolutely right. A mat with air gap between platter and mat is very bad because it doesn't reduce vibrations but introduce unwanted vibrations. To me, a well designed table must have center weight. On my table, it has both center weight and outer ring. Both help to reduce unwanted vibrations. I also spray a thin layer of 3M super 77 on the back of carbon fiber mat and try to hold the mat down. It is ideal to use epoxy to glue the mat on the platter but I am reluctant to do that.
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Will I know it’s not glass as I can cut it with a jigsaw blade made for plexiglass and plastic materials like that and when you cut it does not melt back on itself and it is super super hard to cut and for the statement of small caliber bullet , the 308 is a massive caliber cartridge and I was just showing in that photo the type of energy this stuff will absorb and it is classified as bulletproof ,but my question still is this. , is there anyone out there who would be able to machine two or three of these for me and I will provide them with some of this material so that they can make themselves one or two for themselves
I didn't miss the point you thought it is the most important one. To me, it is not new. A well designed platter couples with groove area completely such as my SME 20. It is not an issue here. For a well designed mat, it is same. My mat is this kind well designed mat.