alighiszem
Go ahead. Put me on your ignore list and ignore my comments. It doesn't mean you are right by doing so. Here is your formula to calculate skating force.Here is the formula in James H. Kogen's classical article on skating force, The Skating-Force Phenomenon.
Judge it for yourself. Isn't your formula complete nonsense!?
I also dug out the article by Tejinder Singh Randhawa in Wireless World, 1978. This is where you quoted the formula from. Here is the diagram. Compare Randhawa's formula with yours. Tell me if they are the same formula.
Fs=F sin(θ)
Is θ the same as your α? Of course not. I don't know what is your α. Your α doesn't make any sense at all.
Let's assume you used the formula correctly for regular pivot tonearm. You also used the same formula for Birch-style tonearm. The reason as you stated to use the same formula is that the stylus on a regular pivot arm and on a Birch-style arm both move following a circle. So, my next question will be which pivot did you use to get the angle θ? Primary, or secondary pivot? Why? Certainly, you didn't use the virtual pivot. If you did, θ will be zero. Fs will be zero, too.
The main problem is that you guys simply ignore the fact you saw with your eyeballs and forced the fact to fit into your own mindset.
Sure. You can ignore me. But the answer is clear.
Fs=F sin(θ)
Is θ the same as your α? Of course not. I don't know what is your α. Your α doesn't make any sense at all.
Let's assume you used the formula correctly for regular pivot tonearm. You also used the same formula for Birch-style tonearm. The reason as you stated to use the same formula is that the stylus on a regular pivot arm and on a Birch-style arm both move following a circle. So, my next question will be which pivot did you use to get the angle θ? Primary, or secondary pivot? Why? Certainly, you didn't use the virtual pivot. If you did, θ will be zero. Fs will be zero, too.
The main problem is that you guys simply ignore the fact you saw with your eyeballs and forced the fact to fit into your own mindset.
Sure. You can ignore me. But the answer is clear.
DD,
Are you serious? As the creator of the wonderful thread, Angling for 90° - tangential pivot tonearms, you should know Birch-style tonearms better than anyone else. Don't you find alighiszem's statements I highlighted above more laughable?
I call the rear pivot in Birch-style tonearm the virtual pivot because this pivot isn't a physical one. However, conceptually, it does exist and it is very important for Birch-style tonearm. I am open to different names for virtual pivot if you find it is confusing.
For the Birch-style arm, the center of the Thales circle is truly virtual. There is nothing that rotates around it.
Last edited:
All the arguments about Birch-style tonearm skates make me rethinking about the design of my Birch-style tonearm, 6B. The goal is further to simplify the structure of the Birch-style tonearm and to reduce the sensitivities of the tower which causes the tonearm skates.
First, I think I may use a single single-row cylindrical roller bearing below.
Secondly, to reduce the height of the gimbal of the tonearm.
First, I think I may use a single single-row cylindrical roller bearing below.
Secondly, to reduce the height of the gimbal of the tonearm.
I will no longer participate in the skating debate from this point forward after this post. I hate to drag Ray back into this. For now I'm sticking to his observations about Birch style arm skating. Not SEEING skating in practice is not the same as no skating in absolute terms. Just like Birch style arms have no tracking error in practice does not mean it is absolutely error free. At the end of the day, a tonearm has to work as a tool in practice and once it reaches a satisfying point, theory becomes just that, theory. Of course one can still continue to pursue perfection, which is welcomed, or other clever ideas such as Doug's recent invention. And I predict more will come from the DIY community and commercial builders.
I for one am quite happy that Birch style arm provides another option for tangential tracking alternative to parallel trackers. First, it's virtually tracking error free. Second, extremely low to no skating force. Third, it allows for conventional bearings without an air pump and/or other attachments such as servo, motor, etc... Fourth, based on builder's sonic evaluation, it sounds good. Fifth, it's DIY-able. Builders like Doug, Jim, Carlo, Trenton, etc... should be celebrated.
I for one am quite happy that Birch style arm provides another option for tangential tracking alternative to parallel trackers. First, it's virtually tracking error free. Second, extremely low to no skating force. Third, it allows for conventional bearings without an air pump and/or other attachments such as servo, motor, etc... Fourth, based on builder's sonic evaluation, it sounds good. Fifth, it's DIY-able. Builders like Doug, Jim, Carlo, Trenton, etc... should be celebrated.
DD,
A major thank you for your eloquent and much needed reply. I regret ever mentioning skating.
Jim,
Your PLT design and build is a serious achievement, but the most important and interesting part of it is not whether it skates.
Doug
A major thank you for your eloquent and much needed reply. I regret ever mentioning skating.
Jim,
Your PLT design and build is a serious achievement, but the most important and interesting part of it is not whether it skates.
Doug
I put a stethoscope to the frame and base of the string suspension arm and didn't hear any needle talk and that was true of the single point string arm, too. My first guess was that the string suspension didn't transmit resonances, but I wasn't sure of that so I tried some tests.
First, I did drop tests with similar length equal diameter tubes of carbon fiber - of the type used for the arm - aluminum, and stainless steel, which all rang as expected, the steel especially loudly. The arm carrier on the actual arm is a stack of Masonite discs. I had some leftover discs and put one on the ends of the tubes and redid the drop test. The carbon and aluminum were significantly damped, but the steel still rang. I think the steel reaction to contact was just more energentic than the others.
Then I suspended the carbon tube from a tensioned string and did as series of tap tests, first hand held then clamped. The tube resonated, but less than when loose. It was louder at the unattached end and less as the taps approached the suspension point and the frequency increased. It also resonated when tapped across the string direction, but not when tapped in the same direction meaning damped in the horizontal and not in the vertical. The resonance was louder hand held than when clamped.
Next, I added one of the Masonite discs to the end of the tube above the suspension and tapped. Ringing was significantly damped. With another disc added sandwiching the string more like the actual arm, the resonance was further damped, although still louder at the loose end. Adding an aluminum piece similar to a head shell to the loose end resulted in a very damped assembly.
These tests are informal at best and I haven't really drawn any conclusions from them, in particular about whether for TTs and TAs it's best to damp resonances immediately or build a path to ground for them or how to do that.
Doug
Doug,
It was important and interesting to me to find out if my 6B skates. The purpose of building my 6B was to find if Birch-style tonearm skates. The result will certainly advance the knowledge about Birch-style arms. If Birch-style arms don't skate, they will have a huge advantage over regular pivot arms.
I don't mind the arguments about skating even if the discussion gets intensive.
If possible, I would like to see you perform my blank disc test on your Birch-style tonearm. I am the only one to perform the blank disc test on a Birch-style arm as far as I know. I would like to see more tests from others to confirm or contradict my test.
Jim
I may be far behind in comprehending this, yet it is still worth understanding to the best of my ability. I was caught up in how the magnetic attractor even works, and then after a few days (yah it can take that long) it started to fall into place. If I had the right tool s to build a more serious model of this tonearm, I would be tempted. When I see inventions such as this, it always makes me wonder why we stick to same old path even if it is pretty fair. Will this just cease to exist 'out there' for the rest of us someday?