Hi,
Stiff does not per definition exclude low self-resonance. When some material as an intrinsically high self-resonance you can damp that to the frequency you want.
Of course there is always going to be a trade off of some sorts.
The beauty of composites is that you can pretty much tune them the way you want.
Not that I expect anyone to shove their home-brewn concoctions into their home-made autoclaves but you wouls expect a piece of arrow as used for the Olympics to be straight and pretty much immune to self-oscillation, wouldn't you?
The arm should be stiff enough to accuratley track without adding its own signature to the sound.
Using high loss materials such as balsa wood can't in any way track the minute changes in groove modulations in the same way a high compliance cartridge can't .
Remember, anything that can move looses energy. The opposite is just as true.
At the end of the day it's all about what you want.
Choose what you want to compromise for it is always going to be a compromise of some sorts. Such is nature.
Cheers,
Stiff does not per definition exclude low self-resonance. When some material as an intrinsically high self-resonance you can damp that to the frequency you want.
Of course there is always going to be a trade off of some sorts.
The beauty of composites is that you can pretty much tune them the way you want.
Not that I expect anyone to shove their home-brewn concoctions into their home-made autoclaves but you wouls expect a piece of arrow as used for the Olympics to be straight and pretty much immune to self-oscillation, wouldn't you?
The arm should be stiff enough to accuratley track without adding its own signature to the sound.
Using high loss materials such as balsa wood can't in any way track the minute changes in groove modulations in the same way a high compliance cartridge can't .
Remember, anything that can move looses energy. The opposite is just as true.
At the end of the day it's all about what you want.
Choose what you want to compromise for it is always going to be a compromise of some sorts. Such is nature.
Cheers,
Frank a ply construction of thin Balsa veneer bonded with the right adhesive (Resorcinol adhesives are very hard rigid and structurally similar to phenolics) and possibly fitted with some some structural ribs can be made to be pretty strong. If you think that it needs to be stiffer then thin layers of metal could always be added where needed. I would opt for a metal head shell assembly. I understand that internal loss and stiffness are two different things and that something can be made stiff and rigid while also having good internal loss characteristics at the same time. I can't see how a rigid carbon fiber tube can be made to have a self resonance of 3 -5 Hz. You will have to explain that to me if there is a way of doing it. A stiff tube with lots of internal loss yes I can see but with a structural resonance as low as you mentioned I just can't imagine. Arrow shafts are very high tech in design and construction and they do get into self resonance which is why they are packed with damping material. With the short lengths we are discussing here for arm wands such a shaft would be quite stiff and internal damping would be for the purpose of dissipating vibrational energy input from the cartridge.
The opposite approach would be to use a very stiff material which you would attempt to damp. An arm wand of thin wall glass for example would be very stiff and transmit energy very effectively this could be damped with a viscose material to absorb both structural resonance from the tube itself as well as energy generated at the cartridge. It would seem to me that either approach could be used to achieve similar results. Cost and handling strength would probably end up being the determining factors.
If you see obvious flaws in my thinking then please point them out because I am here to discuss and to learn. Compromise will as you said always be present I agree. Lets discuss some of them.
One German tonearm designer commented when asked about which arm wand material was best responded by saying that measurements favored metal and high tech composite materials but those customers who purchased by ear for musical qualities consistently preferred wooden arm wands. I thought that was interesting.
The opposite approach would be to use a very stiff material which you would attempt to damp. An arm wand of thin wall glass for example would be very stiff and transmit energy very effectively this could be damped with a viscose material to absorb both structural resonance from the tube itself as well as energy generated at the cartridge. It would seem to me that either approach could be used to achieve similar results. Cost and handling strength would probably end up being the determining factors.
If you see obvious flaws in my thinking then please point them out because I am here to discuss and to learn. Compromise will as you said always be present I agree. Lets discuss some of them.
One German tonearm designer commented when asked about which arm wand material was best responded by saying that measurements favored metal and high tech composite materials but those customers who purchased by ear for musical qualities consistently preferred wooden arm wands. I thought that was interesting.
Hi,
It is not up to me to tell you what to choose.
If you're convinced of the design choices you make then by all means you do not need my blessings.
There are however some drawbacks to using wood for a tonearm I wish to point out:
- hygroscopic
- cellular
- unstable
A carbon rod can be made to resonate at around 4-5 Hz by applying constrained layer damping. Silicone based heatshrink is but one means. Remember the rod is very short.
It is also a very stable material and hard enough so you can apply some mechanical grounding without deforming it.
You do not really need to use that as a material, aluminium would work just the same.
I advise anyoe to really read the paper in the link I gave before.
While the paper does not go into detail about how and why you should apply it throughout your set up, yes even mounting a loudspeaker drive unit a certain way can make for an audible improvement, it does give a basic idea about the thinking involved.
When judiciously applied it makes a world of difference. A difference large enough to make the ordinary sound extraordinary.
Moreover, other than your work it doesn't cost a dyme.
It is the exact same thinking that made designers want to make uni-pivot arms in the first place.
Once they're made to work they are invariably more vivid and dynamic sounding than other multiple bearing designs.
It is all due to mechanical grounding.
Couple energy where needed, decouple where needed. From cartridge to TT, to TT motor, to spindle.
Choice of materials is equally important so you need to know their Q. From vinyl to whatever you choose down the line, you need to make your choice according to the mechanical diode principles or energy will bounce back and forth muddling the signal you so desperately try to extract from the record.
I use suspensionless high mass TTs with an inertia of several tens of tons just sitting on a three legged very light Torlyte table spiked to the floor by three hardened steel spikes.
No acoustic feedback to the cartridge whatsoever.
Why? Why three spikes and legs and not four?
Why does it sound so much closer to a master tape?
Cheers,
It is not up to me to tell you what to choose.
If you're convinced of the design choices you make then by all means you do not need my blessings.
There are however some drawbacks to using wood for a tonearm I wish to point out:
- hygroscopic
- cellular
- unstable
A carbon rod can be made to resonate at around 4-5 Hz by applying constrained layer damping. Silicone based heatshrink is but one means. Remember the rod is very short.
It is also a very stable material and hard enough so you can apply some mechanical grounding without deforming it.
You do not really need to use that as a material, aluminium would work just the same.
I advise anyoe to really read the paper in the link I gave before.
While the paper does not go into detail about how and why you should apply it throughout your set up, yes even mounting a loudspeaker drive unit a certain way can make for an audible improvement, it does give a basic idea about the thinking involved.
When judiciously applied it makes a world of difference. A difference large enough to make the ordinary sound extraordinary.
Moreover, other than your work it doesn't cost a dyme.
It is the exact same thinking that made designers want to make uni-pivot arms in the first place.
Once they're made to work they are invariably more vivid and dynamic sounding than other multiple bearing designs.
It is all due to mechanical grounding.
Couple energy where needed, decouple where needed. From cartridge to TT, to TT motor, to spindle.
Choice of materials is equally important so you need to know their Q. From vinyl to whatever you choose down the line, you need to make your choice according to the mechanical diode principles or energy will bounce back and forth muddling the signal you so desperately try to extract from the record.
I use suspensionless high mass TTs with an inertia of several tens of tons just sitting on a three legged very light Torlyte table spiked to the floor by three hardened steel spikes.
No acoustic feedback to the cartridge whatsoever.
Why? Why three spikes and legs and not four?
Why does it sound so much closer to a master tape?
Cheers,
Hi Frank: I am not looking to be told what to use but for discussion on ideas. I am interested to know what it is about the cellular structure of wood that you consider to make it unacceptable for use in a tonearm wand? Hygroscopic issues along with stability issues can be managed without too much trouble. I would think that a cellular structure especially a fairly random one would be desirable. Does your concern only apply to wood or does it apply to any material of open or closed cell foam?
Hi,
When designing to achieve a goal you do not want to introduce too many variables you just have no way to control let alone reproduce.
When designing a one off you can do as you see fit.
My major concern when using wood is a lack of control.
It is nature at work and therefore seemingly chaotic. Fine for a garden but not if you actually want to channnel energy.
Cheers,
When designing to achieve a goal you do not want to introduce too many variables you just have no way to control let alone reproduce.
When designing a one off you can do as you see fit.
My major concern when using wood is a lack of control.
It is nature at work and therefore seemingly chaotic. Fine for a garden but not if you actually want to channnel energy.
Cheers,
Well Frank I guess I see the random nature of wood cells or foam cells as a way to still conduct energy while at the same time shift and redirect things just a little. In an open cell foam structure each cell will dissipate and direct energy just a little differently from the next and will hopefully minimize structural standing waves within the material. Cell structure is also 3 dimensional so there is even more loss internally. I guess that we just have a different view of what seems desirable. That's ok.
I also think it is a good idea to design in as much loss as possible where you can. Thanks for the suggestion regarding silicone shrink. I never looked at that material as I always thought Silicone would be too reflective but I will give it as try since you have had success with it. Likewise for the link to the Goldmund articles.
Any pictures of your TT and arm to share? It sounds very interesting. Any thoughts on head shell designs? Regards Moray James.
I also think it is a good idea to design in as much loss as possible where you can. Thanks for the suggestion regarding silicone shrink. I never looked at that material as I always thought Silicone would be too reflective but I will give it as try since you have had success with it. Likewise for the link to the Goldmund articles.
Any pictures of your TT and arm to share? It sounds very interesting. Any thoughts on head shell designs? Regards Moray James.
From the sublime to the ridiculous
So tonight I spent several hours listening to and enjoying records using my now functional not quite a Cantus arm. You recall I put together a very lightweight trolley for the new ball bearings. The main member was balsa wood. The whole thing was pretty loosey goosey but it did work and gave me some new reference points and ideas. Last night I built up a nice rigid trolley substituting perspex not unlike Cantus. The armwand, counterweight shaft and bearing mounts are all 1/4" aluminum tube, the actual pieces I've been playing with. Set it up all carefully and listened to a couple of sides. On the whole it performed well enough but it had some rather loud humming with much higher frequency component(s) too. Couldn't figure what it was till the sudden realization I was listening to FEEDBACK. Never heard that before on any tonearm I built. But they all had sand in the arm wands and some silicone fluid as in the WTA designs. So what to do, not wanting to add the extra weight of sand, or powder, or rebuilding the wands in some well damped configuration.
Put a single layer of double sided carpet laying tape around the aluminum tube and then wrapped it with "red" cotton sewing tape like it was a bamboo fly rod. (Why aren't we chopping them up for tone arms?) Set the thing up again and listened to music all evening. Sounded real nice. Could easily crank the gain up all the way with no feedback or other discernible resonances. The evaluation is all highly subjective but it sure worked and can be recommended when a quick fix is needed.
BillG
So tonight I spent several hours listening to and enjoying records using my now functional not quite a Cantus arm. You recall I put together a very lightweight trolley for the new ball bearings. The main member was balsa wood. The whole thing was pretty loosey goosey but it did work and gave me some new reference points and ideas. Last night I built up a nice rigid trolley substituting perspex not unlike Cantus. The armwand, counterweight shaft and bearing mounts are all 1/4" aluminum tube, the actual pieces I've been playing with. Set it up all carefully and listened to a couple of sides. On the whole it performed well enough but it had some rather loud humming with much higher frequency component(s) too. Couldn't figure what it was till the sudden realization I was listening to FEEDBACK. Never heard that before on any tonearm I built. But they all had sand in the arm wands and some silicone fluid as in the WTA designs. So what to do, not wanting to add the extra weight of sand, or powder, or rebuilding the wands in some well damped configuration.
Put a single layer of double sided carpet laying tape around the aluminum tube and then wrapped it with "red" cotton sewing tape like it was a bamboo fly rod. (Why aren't we chopping them up for tone arms?) Set the thing up again and listened to music all evening. Sounded real nice. Could easily crank the gain up all the way with no feedback or other discernible resonances. The evaluation is all highly subjective but it sure worked and can be recommended when a quick fix is needed.
BillG
It would be a lot of work but you might want to try packing the tubes with powder. I am not sure how firmly you would need to pack it in. I should think that need to be pretty firm but not necessary to be solid. The Arrow guys use white powder coffee creamer to damp shafts. You could also try activated charcoal powder or Perlite powder which is probably lighter than the coffee creamer or charcoal. You will need to close off the tubes ends with blue tack or the like to maintain compression of the powder as it will have to make firm contact with the tube walls.
Do you think that the perspex trolley structure works better than the Balsa version? I would imagine that a few wet coats of soft lacquer would provide surface skin damping to the tubes and would be lighter than the double sided tape and thread wrap. Nail polish would work as it is firm but must be flexible so it wont crack or chip off of long nails. Either option would likely weigh less than a layer of shrink tube but you could try that first cheap and easy to remove or replace if you decided that you liked it. Frank's suggestion was for silicone shrink. Costs a little more but worth a try as well. I was thinking that fudging the length of the arm tube so that the head shell, counter weight and contact point with the carriage assembly all fell on nodal points along the length of the arm wand could help too. You might not be able to get all the points to align but it would be worth looking at. Would be interesting to compare to small diametre thin wall tubes such as Bo uses. See if there is a saving in weight and any improvement in performance.
Running a cartridge like a Decca would tell you where the rattles in the system are. I should think that the lower the compliance of the cartridge the more weight you would need to have in the assembly to keep it from jumping around. So you could have a lighter assembly for high compliance cartridges.
Has anybody considered different ideas for head shell configurations to eat up energy from the cartridge at the source? I was thinking rigid in the horizontal plane and building in some loss in the direction of the arm tube(s). You would need to provide a rigid coupling from the head shell to the arm wand but there would be plenty of room to include some wide band lossy material as well. I have also seen adjustable out rigger weight on either side of the cartridge to help keep it stable. Am just throwing out ideas here. Regards Moray James.
Do you think that the perspex trolley structure works better than the Balsa version? I would imagine that a few wet coats of soft lacquer would provide surface skin damping to the tubes and would be lighter than the double sided tape and thread wrap. Nail polish would work as it is firm but must be flexible so it wont crack or chip off of long nails. Either option would likely weigh less than a layer of shrink tube but you could try that first cheap and easy to remove or replace if you decided that you liked it. Frank's suggestion was for silicone shrink. Costs a little more but worth a try as well. I was thinking that fudging the length of the arm tube so that the head shell, counter weight and contact point with the carriage assembly all fell on nodal points along the length of the arm wand could help too. You might not be able to get all the points to align but it would be worth looking at. Would be interesting to compare to small diametre thin wall tubes such as Bo uses. See if there is a saving in weight and any improvement in performance.
Running a cartridge like a Decca would tell you where the rattles in the system are. I should think that the lower the compliance of the cartridge the more weight you would need to have in the assembly to keep it from jumping around. So you could have a lighter assembly for high compliance cartridges.
Has anybody considered different ideas for head shell configurations to eat up energy from the cartridge at the source? I was thinking rigid in the horizontal plane and building in some loss in the direction of the arm tube(s). You would need to provide a rigid coupling from the head shell to the arm wand but there would be plenty of room to include some wide band lossy material as well. I have also seen adjustable out rigger weight on either side of the cartridge to help keep it stable. Am just throwing out ideas here. Regards Moray James.
Frank: I do look forward to your constructive criticism. Sounds like you are itching to teach us a thing or two and I am here to learn. I still want to see your table Frank can you post a picture? What about building an energy sink into a head shell? The engineer is outside of the box right now looking for more ideas. Engineering is not all it's cracked up to be. Look at how many beers they have to drink just to get through university.
James
Do you really think that it will come to an arrangement,well,sort of ?
Forums exist ,for everyone to sign in and say his say.
Come to audio,and you will be ridiculed,scolded,minced,killed,simply because either you don't get it ,or you have other ways of doing it.
Our microcosm is filled with killer designers and engineers,that won't accept other voices.They want us to listen with their ears and measuring devices.
They don't know in their tiny algebra minds that by killing ideas you are halting progress.
Anyways...
A good design,as most of us assume,is one that is repeatable and costs so that it will be sellable.
It doesn't pay to design a fly killing "Big Bertha" cannon.Everyone can do it,when cost is no object.But a 50 cent plastic thingy is more applicable.
Scientific community,tends to forget that we, simple ,plain, every day hobbits ,are in a hobby to pass our spare time,and do something that our free not scientific minds,find easy to grasp and make.Without spending vast sums of monies for ready made goodies.
We are simply havin' fun.
If you are in agreement with that,we can continue,exchanging ideas and such.Otherwise it is simply unwise.
B.L.
B.L. it can be difficult to understand what someone is saying harder to understand what they mean and you may never know what they are thinking or how they feel much less what makes them feel the way they do. So pick out the bits that help and be grateful that you found some good along the way. Give as much back as you take and things even out in the end. Give back more and you will have a lot of happier Hobbits.
I couldn't agree more.
BTW, I saw a you tube presentation of a linear arm ,made by a guy in Japan,
that uses slide bearings.Although over-engineered,it is too clever to be ignored.
Therefore yesterday an order was placed to a co. named Small Parts,(affiliated to Amazon)somewhere in the vast USA. Total cost for the bearing and the slide rod $ 33.5,shipping included,to the far out Mediterranean Greece,that I am living.
The bearing is THK LM8 and the rod is THK SF 8.
The guy in the video uses 6 mm bearing and rod,but what the hell.I am not going to copy it step by step,only the linear slide is going to be the same.After all,we are having good time.And if it doesn't work,first time,we can have endless iterations.
So bye bye Swedish Rauna and Cantus ,hello Japan
B.L.
Yes directdriver pointed the Japanese site out some time back. He can make a bike for me any day. Amazing the skill some folks have. I am sure that the design will work and be a lot of fun. It follows more closely what Lou Souther was doing with Lou's design being less complex and lower in overall moving mass. Fluid damping could be applied to control the Japanese arms radial motion (along the lines of Max Townhend's The Rock home). Direct driver has a Souther arm and has posted pictures perhaps he might take some additional pictures of the mechanism. Bo Hansson is on the other hand looking to eliminate unwanted motion which can become resonant and so the ball bearings which can only roll in the horizontal plane but which can slide up and down the glass tube wall to accommodate the tracking of warps. Have fun and let us know how the new arm compares to the factory built arms you have used.
Truth to be told,I do not know,if the friction levels are higher or not.But I will find it the hard way.By trying.
Keep in mind though,that the " Kiirojbl " implementation is an excercise in engineering targeting many other areas,sound behaviour included.
The arm doesn't have to be built like a Transformers toy,which it is, as shown.No offence to the man who made it.
By building on the idea the horizontal friction and the moving mass of the arm,are easily altered by using lighter materials,as plexi or hardwoods,and the armwand too,will be shortened to "simply holding the cartridge dimensions".
Cartridge tracking and therefore ,friction lowering,can be augmented by lowering the inner part of the slider rod,a degree or two.
And as M.J.wrote ,I could use fluid damping for controling spurious,bearing movement.
Do not forget the negative comments for the original "ROCK",which after all was a univercity experiment that became commercial.The funny thing was and is that it was functioning the way it was presented that would function.
But it was Linn times,and everything else were lemons.Do you remember that?
I cannot see ways for it to go wrong.After all,the drawing board is always there.
B.L
BL: I think that the Japanese design will work well and I agree that it could be built to have a reasonable moving mass. Fluid damping could be applied at the cartridge end or at the main bearing end (probably more user friendly). I remember the "Ivor" days and that the earth was flat. Max Townshend is a good guy and makes solid products.
Can you elaborate on the comment you made about lowering friction by lowering the inner part of the slider rod a degree or two. I am not understanding this. Thanks.
Can you elaborate on the comment you made about lowering friction by lowering the inner part of the slider rod a degree or two. I am not understanding this. Thanks.
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