I'm going to build a variant on the Altmann DIY Unipivot tonearm, using a hollow carbon fibre shaft (from an arrow) for the armtube (since it is stiffer, straighter and will shield the wires from EMI & RF). However, I'm worried that there may be a certain amount of resonance inside the tube, and I'm wondering what folks think is the best way to damp this resonance.
I was considering expanding insulating foam, but I'm not sure how well this would work, given that the inner diameter of the tube is smaller than the diameter of the nozzle. Also, I want something that isn't going to potentially eat through the tonearm wire insulation. I have six arrows, so I can afford to make mistakes (since this is my first tonearm project), but I'd like to try and get it right the first time.
Thanks!
-Derek
I was considering expanding insulating foam, but I'm not sure how well this would work, given that the inner diameter of the tube is smaller than the diameter of the nozzle. Also, I want something that isn't going to potentially eat through the tonearm wire insulation. I have six arrows, so I can afford to make mistakes (since this is my first tonearm project), but I'd like to try and get it right the first time.
Thanks!
-Derek
Outer damping
I have used thin wall aluminum tube of slightly larger diameter as an outer layer, filling the gap between two with silicone caulk (3/8" fits well to 8 mm carbon tube). This kind of sandwich is called constraint layer damping (CLD), and has extremely good damping properties. One thing to remember: a headshell and bearing should be connected to the inner (carbon) tube to keep whole assembly rigid.
Inner damping with foam is next to nothing (I came across telescope builder forum, they have gained alot of experience regarding tubes damping).
Good luck
Michael
I have used thin wall aluminum tube of slightly larger diameter as an outer layer, filling the gap between two with silicone caulk (3/8" fits well to 8 mm carbon tube). This kind of sandwich is called constraint layer damping (CLD), and has extremely good damping properties. One thing to remember: a headshell and bearing should be connected to the inner (carbon) tube to keep whole assembly rigid.
Inner damping with foam is next to nothing (I came across telescope builder forum, they have gained alot of experience regarding tubes damping).
Good luck
Michael
What is "Silicone Caulc"?
Is it the standard "hardening" silicone sealant one uses for bathroom duty etc?
Do you have further references to constrained layer damping?
Petter
Is it the standard "hardening" silicone sealant one uses for bathroom duty etc?
Do you have further references to constrained layer damping?
Petter
Constraint layer damping
Hi Petter,
Yes, I use the houshold colorless bath silicone sealant, which remains rather soft after "hardening".
CLD is widely used when good dampening properties should be combined with low total mass - exactly the case of arm tube.
Do google search, if you need some theoretical background - I can't recall specific link.
One more place I plan to implement CLD principle is underneath the platter - kind of "reversed sorbothane mat". Again, two things to remember: 1. CLD sandwitch consist of soft layer and rigid one above it, providing soft layer is faced dampened surface; 2. do not compromise platter-bearing-plinth-shelf chain stiffness by inserting soft layer somewhere inbetween.
Regards,
Michael
Hi Petter,
Yes, I use the houshold colorless bath silicone sealant, which remains rather soft after "hardening".
CLD is widely used when good dampening properties should be combined with low total mass - exactly the case of arm tube.
Do google search, if you need some theoretical background - I can't recall specific link.
One more place I plan to implement CLD principle is underneath the platter - kind of "reversed sorbothane mat". Again, two things to remember: 1. CLD sandwitch consist of soft layer and rigid one above it, providing soft layer is faced dampened surface; 2. do not compromise platter-bearing-plinth-shelf chain stiffness by inserting soft layer somewhere inbetween.
Regards,
Michael
Hi,
Yep...We don't want to build a matrass..😉
The carbon pipes cut from arrows shouldn't need anymore extra damping really...Too much damping will give you a rather dull, lifeless sound...
Happy holidays,😉
Yep...We don't want to build a matrass..😉
The carbon pipes cut from arrows shouldn't need anymore extra damping really...Too much damping will give you a rather dull, lifeless sound...
Happy holidays,😉
That helps, Frank. I was trying to find suitable copper or brass tubes that were just a hair smaller than the inner diameter of the arrow shafts. Now I guess I won't have to worry about that! 😀
Next step: ordering a sapphire bearing and point from Small Parts and machining a bearing cup and counterweight out of ebony or walnut (going for wood instead of metal as the arrow shaft is so darned light!). The tough part is going to be trying to find someone to build me a headshell out of aluminum.
I guess I'm sorta defeating the purpose of the Altmann DIY Unipivot by spending this much time and money...<sigh>
-Derek
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