It is very difficult to determine the values of damping generated by a linear arm or a tangential pivot tonearm. For some of the linear arms, the damping in the vertical plane is different from the lateral plane.
There are many test LPs that have vertical or lateral tracks. Take Ultimate Analog Test LP as an example. It has a vertical pink noise track and a lateral pink noise track. Using these tracks will give you the information on vertical and lateral resonance frequencies. Please see my air bearing thread for testings.
There are many test LPs that have vertical or lateral tracks. Take Ultimate Analog Test LP as an example. It has a vertical pink noise track and a lateral pink noise track. Using these tracks will give you the information on vertical and lateral resonance frequencies. Please see my air bearing thread for testings.
Hi - thanks for the hints: I know your interesting measurements, super1008 - and sometimes looked at your LP group buy, Icsaszar.
However, for me a test disc (but I have always used just an old Decca record, on which there are most of the signals you've mentioned, even if too short) is a great help to evaluate a cartridge and its setup (starting from matching) but much less for an arm. Especially if the signal is taken from the cartridge, and not from an accelerometer, as done by Alexej Korf, who is sharing his great work on TAs, or with the clever Walter invention (with a second cartridge -# 2376 DIY linear thread).
Unavoidably you're measuring the sum of what comes out of the cartridge (greatest source by far, hopefully) + TA feedback, without knowing:
- how the cutting reproduces the master signal (as evidenced in your post # 417)
- what kind of resonances emerge from the body of the cartritge itself
- how the eff. masses really act through the complex and inhomogeneous compound of a tonearm
- and so on.
Too indirect measures, too many elements involved, too many uncontrolled variables: as said, great for checks, tuning and comparison, but not so much in providing useful data for TA design. That's why it would be convenient to find a method for horizontal eff. mass calculation even for our PLTs.
carlo
Once i had the silly idea to bypass completely the cartridge+test disc, simply placing the TA through a rigid pin on a mini speaker, or piezo buzzers of various frequencies, reading what happens at the headshell, shaft, CW and bearings level. But since ì'm unable to program Arduino or Raspy, never tried
However, for me a test disc (but I have always used just an old Decca record, on which there are most of the signals you've mentioned, even if too short) is a great help to evaluate a cartridge and its setup (starting from matching) but much less for an arm. Especially if the signal is taken from the cartridge, and not from an accelerometer, as done by Alexej Korf, who is sharing his great work on TAs, or with the clever Walter invention (with a second cartridge -# 2376 DIY linear thread).
Unavoidably you're measuring the sum of what comes out of the cartridge (greatest source by far, hopefully) + TA feedback, without knowing:
- how the cutting reproduces the master signal (as evidenced in your post # 417)
- what kind of resonances emerge from the body of the cartritge itself
- how the eff. masses really act through the complex and inhomogeneous compound of a tonearm
- and so on.
Too indirect measures, too many elements involved, too many uncontrolled variables: as said, great for checks, tuning and comparison, but not so much in providing useful data for TA design. That's why it would be convenient to find a method for horizontal eff. mass calculation even for our PLTs.
carlo
Once i had the silly idea to bypass completely the cartridge+test disc, simply placing the TA through a rigid pin on a mini speaker, or piezo buzzers of various frequencies, reading what happens at the headshell, shaft, CW and bearings level. But since ì'm unable to program Arduino or Raspy, never tried
Hi all,
Determining the horizontal effective mass of a PLT mathematically would be a PITA.
With a conventional pivoted arm the entire motion is rotational about a fixed point and its effective mass is the polar inertia about this point as measured at the stylus. Relatively simple but laborious to calculate.
With a linear arm the horizontal effective mass is the total carriage mass so is a piece of cake to work out.
Most PLTs combine both rotation and translation.
To calculate the effective mass you need to calculate the contribution from each type of motion and add them together. The rotational contribution of the main arm/counterweight /headshell /cartridge can be determined as if it were a conventional pivoted arm. To determine the linear translations contribution you need to work out how far the centre of mass of the arm moves relative to the amount the stylus moves and multiple this by the mass of the arm. So if the center of mass moves one tenth the amount the stylus moves the linear translations contribution will be one tenth the mass of the main arm. It is only the amount the arm moves that matters for this calculation and not the direction. The effective mass of the other moving linkages would need to be determined in a similar way taking both rotation and translation into account.
As the arm tracks across the record the amount of translation movement will vary so the effective mass will actually also vary slightly. This effect will probably be way to small to be of any concern but is would be useful/interesting to calculate how this varies.
As you can see the amount of work required to calculate the overall effective mass is substantial and a single simple method isn't possible. The use of a spreadsheet will be pretty much essential. Unfortunately you couldn't really make a universal spreadsheet as making it accommodate all design variables would render it to difficult to use.
Another quick reply to a point made recently. The addition of damping does not alter effective mass. It will reduce the amplitude of the resultant resonant peek and may cause the frequency of shift to a sightly lower frequency. If critically damped it may make using a test record to determine effective mass very difficult.
Niffy
Determining the horizontal effective mass of a PLT mathematically would be a PITA.
With a conventional pivoted arm the entire motion is rotational about a fixed point and its effective mass is the polar inertia about this point as measured at the stylus. Relatively simple but laborious to calculate.
With a linear arm the horizontal effective mass is the total carriage mass so is a piece of cake to work out.
Most PLTs combine both rotation and translation.
To calculate the effective mass you need to calculate the contribution from each type of motion and add them together. The rotational contribution of the main arm/counterweight /headshell /cartridge can be determined as if it were a conventional pivoted arm. To determine the linear translations contribution you need to work out how far the centre of mass of the arm moves relative to the amount the stylus moves and multiple this by the mass of the arm. So if the center of mass moves one tenth the amount the stylus moves the linear translations contribution will be one tenth the mass of the main arm. It is only the amount the arm moves that matters for this calculation and not the direction. The effective mass of the other moving linkages would need to be determined in a similar way taking both rotation and translation into account.
As the arm tracks across the record the amount of translation movement will vary so the effective mass will actually also vary slightly. This effect will probably be way to small to be of any concern but is would be useful/interesting to calculate how this varies.
As you can see the amount of work required to calculate the overall effective mass is substantial and a single simple method isn't possible. The use of a spreadsheet will be pretty much essential. Unfortunately you couldn't really make a universal spreadsheet as making it accommodate all design variables would render it to difficult to use.
Another quick reply to a point made recently. The addition of damping does not alter effective mass. It will reduce the amplitude of the resultant resonant peek and may cause the frequency of shift to a sightly lower frequency. If critically damped it may make using a test record to determine effective mass very difficult.
Niffy
Determining the horizontal effective mass of a PLT mathematically would be a PITA. (Niffy)
Even though we Italians love our Pizza (PITA for the ancient romans & greeks) I had to search on web for translation: thanks Niffy, you and Ray (a math nightmare ...) have perfectly framed the situation; otherwise someone would have succeeded since a long time.
I'm glad, however, that my attempt of analysis # 2258 wasn't completely off road. So now i'm dealing with this super-rough method: the subsystem B contributes 2/3 ca, while that of the compound A of all the mobile masses for the rest, slightly growing on the inner grooves. This ratio varies somehow with the Thales circle employed, which determines the amount of forward motion in a Birch PLT.
So the sum should be less than simply adding the mass of the pulley+cranks+bearings directly to the eff. mass of the sub arm, as I thought while designing the Rabbit. And the variation, too, seems less worrying than that of the contribution to the motion from the S.D. vs S.F.
Better than nothing, maybe - but is it there a non-mathematical method to get it?
carlo
Even though we Italians love our Pizza (PITA for the ancient romans & greeks) I had to search on web for translation: thanks Niffy, you and Ray (a math nightmare ...) have perfectly framed the situation; otherwise someone would have succeeded since a long time.
I'm glad, however, that my attempt of analysis # 2258 wasn't completely off road. So now i'm dealing with this super-rough method: the subsystem B contributes 2/3 ca, while that of the compound A of all the mobile masses for the rest, slightly growing on the inner grooves. This ratio varies somehow with the Thales circle employed, which determines the amount of forward motion in a Birch PLT.
So the sum should be less than simply adding the mass of the pulley+cranks+bearings directly to the eff. mass of the sub arm, as I thought while designing the Rabbit. And the variation, too, seems less worrying than that of the contribution to the motion from the S.D. vs S.F.
Better than nothing, maybe - but is it there a non-mathematical method to get it?
carlo
Hi Niffy, I believe it's possible to approach a general formula in the way described but it might be unnecessarily complicated.
Been bumping my head on this problem for a while and I suspect there is a general solution to this problem, but there would have to be some assumptions to reduce the complexity.
Pivoting and linear TA could also benefit from that solution as some values would be zero or close to it.
What say you about the following possible solution?
All pivoting tangential TAs are compound objects, fortunately a compound object's moment of inertia (MOI) is just a sum of the MOI of the rigid parts at the centre of mass (COM) of each part.
I use the COM of each part (from modelling) as you can completely ignore the translation part of the motion (of the compound object).
That sum is the MOI of the compound object at the COM of the compound object. You should be able to calculate that by taking a 2d slice of the object and using the material density.
The final step is to calculate the MOI at the effective length, you might need the difference between the COM of the compound object and the effective length for that.
This is only for the horizontal effective mass at a certain point as it is variable.
Vertical can then be calculated from the method here.
The assumptions are that this calculation is in a vacuum and there are no losses due to friction etc.
Still, not a simple solution but doable.
Hi Niffy and 2wice, I am happy to have rocked the boat, involving your great knowledge. Knowing the eff. masses is one of the basic parameters to know what kind of TA we are setting up, but beyond the practical effects for PLTs seems also a challenging theoretical problem.
Another doubt: the Hor. eff. mass must be calculated with respect to the fixed pivot or the mobile one?
carlo
Another doubt: the Hor. eff. mass must be calculated with respect to the fixed pivot or the mobile one?
carlo
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Hi Carlo
I calculate Horizontal effective mass from the fixed pivot and vertical from the moving pivot.
Hi all,
In my previous post I wrote "The rotational contribution of the main arm/counterweight /headshell /cartridge can be determined as if it were a conventional pivoted arm." This statement was incomplete. The rotational contribution will tend to be less than this. For a certain amount of movement of the stylus the pivot will also move a bit. The actual rotational contribution will be determined by the ratio of the movement of the stylus the movement of the stylus minus the movement of the pivot. This ratio multiplied by the mass calculated as previously described will give the rotational contribution.
Unfortunately this makes calculation slightly more cumbersome.
The friction of the bearings will not effect effective mass though it will act in a similar way to damping.
Niffy
In my previous post I wrote "The rotational contribution of the main arm/counterweight /headshell /cartridge can be determined as if it were a conventional pivoted arm." This statement was incomplete. The rotational contribution will tend to be less than this. For a certain amount of movement of the stylus the pivot will also move a bit. The actual rotational contribution will be determined by the ratio of the movement of the stylus the movement of the stylus minus the movement of the pivot. This ratio multiplied by the mass calculated as previously described will give the rotational contribution.
Unfortunately this makes calculation slightly more cumbersome.
The friction of the bearings will not effect effective mass though it will act in a similar way to damping.
Niffy
Well, I'll throw out a post on this topic of effective mass. This will not answer the question... But from a practical point the lateral effective mass will be a lot lower than my homebuilt Ladegaard LT arm, which requires much lower compliance. No way could I have tried for an LT arm for any of my favorite high compliance carts. In the LT clone I'm attempting I currently have effective mass of the arm down to ~ 8gm, using traditional pivot measurements. I don't think the part of the mass that would need to be added to get the equation correct a for PLT arm is going to make a big difference. I think using an accurate test record will probably tell us something on this...
mcspack,
most of LT arms are not working with high compliance carts well. I do not see a problem here, because usually any kind of tonearm will not accept both low and high compliance carts well. LT arms are for medium to low compliance carts, and there are many of excellent MC carts like that, including most expensive and well sounding.
The only one exception among LT's I know for now, is Carlo's Lil Casey.It works excellent with wide range of different compliance cartridge, and sound range is from very good to amaizing. I had a listening session with $5000 Wilson Benesh Carbon, and $7800 Van Den Hul Collibri on Lil Casey arm 3 days ago, and was completely blown off by the sound. As I said before, the same arm worked well with high compliance Ortofon VMS20EO and Shure V15 type3, they sounded very well.
Carlo, despite I'm writing about your Lil Casey again, I'm rather speachless...
I'm very sceptical by nature, but now I surrender to facts. There is a substantial difference in sound between hi-fi cart and hi-end one, if used on proper arm in proper system.
most of LT arms are not working with high compliance carts well. I do not see a problem here, because usually any kind of tonearm will not accept both low and high compliance carts well. LT arms are for medium to low compliance carts, and there are many of excellent MC carts like that, including most expensive and well sounding.
The only one exception among LT's I know for now, is Carlo's Lil Casey.It works excellent with wide range of different compliance cartridge, and sound range is from very good to amaizing. I had a listening session with $5000 Wilson Benesh Carbon, and $7800 Van Den Hul Collibri on Lil Casey arm 3 days ago, and was completely blown off by the sound. As I said before, the same arm worked well with high compliance Ortofon VMS20EO and Shure V15 type3, they sounded very well.
Carlo, despite I'm writing about your Lil Casey again, I'm rather speachless...
I'm very sceptical by nature, but now I surrender to facts. There is a substantial difference in sound between hi-fi cart and hi-end one, if used on proper arm in proper system.
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Thxs Walter: so I'll have to resign myself to the idea of being a genius without knowing, or at least an inexplicably lucky diyer.
I'm joking, but will it be thanks to the Lil Casey's radial rail, or to the scent of the price of those cartridges? I have still to meet a Ferrari owner (there were some, between the customers of our studio) admit that it was a more unreliable car than a Trabant (back to the workshop every 4-5000 km).
I am noticing too the strange ability of LilCasey to work well with very different cartridges, and I am wondering why: perhaps because practically there is nothing else added (if not ten grams of carriage) and therefore each cartridge sounds at it likes? differences are much more evident than usual.
What's your idea?
carlo
I'm joking, but will it be thanks to the Lil Casey's radial rail, or to the scent of the price of those cartridges? I have still to meet a Ferrari owner (there were some, between the customers of our studio) admit that it was a more unreliable car than a Trabant (back to the workshop every 4-5000 km).
I am noticing too the strange ability of LilCasey to work well with very different cartridges, and I am wondering why: perhaps because practically there is nothing else added (if not ten grams of carriage) and therefore each cartridge sounds at it likes? differences are much more evident than usual.
What's your idea?
carlo
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Thanks Walter,
I should explain. When I originally started building my Ladegaard arm I was a complete newb regarding phono arms, their mass etc. I had hoped to use it with high compliant carts then learnt the hard way, lol. When the Schroder LT arm came into fruition that changed things, I hope. Some here feel a clone of it is possible, I will soon find out. My point was that the Schroder arm, as I'm building it, should work for my favorite high compliance carts.
I should explain. When I originally started building my Ladegaard arm I was a complete newb regarding phono arms, their mass etc. I had hoped to use it with high compliant carts then learnt the hard way, lol. When the Schroder LT arm came into fruition that changed things, I hope. Some here feel a clone of it is possible, I will soon find out. My point was that the Schroder arm, as I'm building it, should work for my favorite high compliance carts.
1) I'm joking, but will it be thanks to the Lil Casey's radial rail, or to the scent of the price of those cartridges? I have still to meet a Ferrari owner (there were some, between the customers of our studio) admit that it was a more unreliable car than a Trabant (back to the workshop every 4-5000 km).
2) I am noticing too the strange ability of LilCasey to work well with very different cartridges, and I am wondering why: perhaps because practically there is nothing else added (if not ten grams of carriage) and therefore each cartridge sounds at it likes? differences are much more evident than usual.
What's your idea?
carlo[/QUOTE] As to the first, no way. In my own system (on medium mass pivot Micro arm) Benesh sounded mediocre, and I was convinced that such cartridge is kind of smart marketing success in order to sell average product for lot of $$$. Untill I've heard the same cart on Lil Casey, with a much better system of other audiophile. Honestly, I liked the sound even more, than more expensive Colibri sound ( on Lil Casey too), which is also outstanding. Price doesn't rule here.
As to the second, Lil Casey is completely different animal, comparing to known arms. It looks like it doesn't add to the sound it's own coloration and distortions. Moves efortlessly enough to work well with high compliance carts due to linear balls movement. I suppose, it is grounded very well too. Who knows what else, there is a lot of things to study and understand.
Walter
2) I am noticing too the strange ability of LilCasey to work well with very different cartridges, and I am wondering why: perhaps because practically there is nothing else added (if not ten grams of carriage) and therefore each cartridge sounds at it likes? differences are much more evident than usual.
What's your idea?
carlo[/QUOTE] As to the first, no way. In my own system (on medium mass pivot Micro arm) Benesh sounded mediocre, and I was convinced that such cartridge is kind of smart marketing success in order to sell average product for lot of $$$. Untill I've heard the same cart on Lil Casey, with a much better system of other audiophile. Honestly, I liked the sound even more, than more expensive Colibri sound ( on Lil Casey too), which is also outstanding. Price doesn't rule here.
As to the second, Lil Casey is completely different animal, comparing to known arms. It looks like it doesn't add to the sound it's own coloration and distortions. Moves efortlessly enough to work well with high compliance carts due to linear balls movement. I suppose, it is grounded very well too. Who knows what else, there is a lot of things to study and understand.
Walter
hi mcspack - having built some PLTs I would like to be helpful.
First of all, what effective mass you are talking about? the horizontal if i'm understanding well. Surely you'll have read the recent debate here, and how the calculation is not easy to solve (#2258): hoping for those who have the mathematical knowledge to succeed, someday.
You're asking if an LT clone can work with a high compliance cartridge: can't answer directly, but my realizations sound better with medium to high compliance MMs than with Denon MCs. However, consider that the masses were reduced as much as possible, both for vertical (on the Rabbit PLT there is even a spring CW for this) and horizontal. Normally on a PLT the shaft is shorter than on pivoted ones, and the consequent vertical mass comes out naturally reduced.
For an LT clone it's difficult to evaluate the effect of the magnetic guide because each case is different from the other. It does not change the effective mass, but it is certainly a very important dampening.
Which geometry do you intend to use for your LT? unfortunately there are endless (# 2146).
carlo
Who knows what else, there is a lot of things to study and understand. Walter
Quote your observations, grounding included: those small balls play a lot of useful works...
First of all, what effective mass you are talking about? the horizontal if i'm understanding well. Surely you'll have read the recent debate here, and how the calculation is not easy to solve (#2258): hoping for those who have the mathematical knowledge to succeed, someday.
You're asking if an LT clone can work with a high compliance cartridge: can't answer directly, but my realizations sound better with medium to high compliance MMs than with Denon MCs. However, consider that the masses were reduced as much as possible, both for vertical (on the Rabbit PLT there is even a spring CW for this) and horizontal. Normally on a PLT the shaft is shorter than on pivoted ones, and the consequent vertical mass comes out naturally reduced.
For an LT clone it's difficult to evaluate the effect of the magnetic guide because each case is different from the other. It does not change the effective mass, but it is certainly a very important dampening.
Which geometry do you intend to use for your LT? unfortunately there are endless (# 2146).
carlo
Who knows what else, there is a lot of things to study and understand. Walter
Quote your observations, grounding included: those small balls play a lot of useful works...
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Thanks, I know this won't be the first PLT attempt built here and I applaud the efforts of others. Yes, it is possible to separate the lateral and vertical eff mass for a PLT, but why? Compared to my Ladergaard LT lateral eff mass is probably orders of magnitude less. It CAN be built using standard pivot eff mass calcs to play nice with high and even very high compliance carts. I asked Herr Schroder this very question before I decided to try and build a clone. In the end, I may still have him build me one but that shouldn't discourage others from trying to build one of these PLTs if they have a similar cart. 
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Best wishes for your realization, and keep us informed on your results: after several different efforts built, many here are eager to see a new LT clone at work.
PLT eff. masses
What a mathematical nightmare - Ray K
Determining the horizontal effective mass of a PLT mathematically would be a PITA. - Niffy
Been bumping my head on this problem for a while. and I suspect there is a general solution to this problem, but there would have to be some assumptions to reduce the complexity. - 2wice
Could you please tell me how to calculate the horizontal mass of a PLT "using standard pivot eff mass calcs"? If you mean the known formulas used for pivoted ones I just can't imagine how, for what seems to me a completely different, and very complex situation.
carlo
PLT eff. masses
What a mathematical nightmare - Ray K
Determining the horizontal effective mass of a PLT mathematically would be a PITA. - Niffy
Been bumping my head on this problem for a while. and I suspect there is a general solution to this problem, but there would have to be some assumptions to reduce the complexity. - 2wice
Could you please tell me how to calculate the horizontal mass of a PLT "using standard pivot eff mass calcs"? If you mean the known formulas used for pivoted ones I just can't imagine how, for what seems to me a completely different, and very complex situation.
carlo
I have no Idea how to calculate it, my point is to use standard pivot methods, ie verticle, to guess what the entire eff mass is. I'm sure PLT eff mass is a bit more, but only a bit. In Herr Schroder's realization, eff mass laterally has to be vanishingly small, moment of enertia, for his arm to work, right? I'm guessing.
Needless to repeat what discussed beginning from post # 2253.
On every PLT (none excluded) the hor. "effective mass" is always bigger than the vertical one because the vertically moving masses (cartridge + headshell + shaft + CW) are added to those necessary (crank + bearings + guide) for the horizontal movement. The complexity of this movement (rotation + advance) makes the calculation very problematic.
carlo
If you haven't done before, please look at Doug's (Dtut) valuable work (pages 76-77-82-84-85-86), which realization maybe remains the only working LT clone seen on this thread.
There were other announcements and attempts, but then the traces were lost.
On every PLT (none excluded) the hor. "effective mass" is always bigger than the vertical one because the vertically moving masses (cartridge + headshell + shaft + CW) are added to those necessary (crank + bearings + guide) for the horizontal movement. The complexity of this movement (rotation + advance) makes the calculation very problematic.
carlo
If you haven't done before, please look at Doug's (Dtut) valuable work (pages 76-77-82-84-85-86), which realization maybe remains the only working LT clone seen on this thread.
There were other announcements and attempts, but then the traces were lost.