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Old 6th June 2013, 03:55 AM   #511
tnargs is offline tnargs  Australia
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Quote:
Originally Posted by awolff761 View Post
Hi, tnargs,
Thanks for checking my post, but my reading of Poul's arm is different. He says (Poul Ladegaard's Air Bearing Tangential Tonearm Page),....
Quote:
Originally Posted by directdriver View Post
Care to elaborate your claim that horizontal mass has no effect on performance? Besides sonic performance, how do you deal with eccentric records? Enlighten us.
Hi guys, if I were you I wouldn't want to rely on me for your enlightenment, but here goes:

Firstly, the forces involved in moving an arm from the edge to the centre of an LP, are much less than the forces resulting from eccentricity of the hole. So let's confine discussion to the latter.

Andy quoted the right document but the wrong extract. Referring to Ladegaard's #3 (final) arm, he wrote:

The arm and carriage weigh 160 grams altogether, which was increased up to a total of 300 grams with two triangular lead weights.

Now one might fear that poorly centered records would provoke the stylus too much when it has to move so much 'baggage'. .... On the arms described here, the load was typically around +/- 50 milligrams. This is insignificant compared to a normal tracking force of 1.8 grams.


This is on an arm weighing three hundred grams! A typical Airtangent-type has maybe one eighth of this sliding mass.

How significant is one eighth of 'insignificant'? And that is only with poorly centred records.


Another perspective: let's look at the uncorrected lateral forces on a stylus attached to a pivot arm. A typical figure for constant skating force is 200 milligrams, plus a modulation skating force peaking at 200 milligrams (Kogen, 1967). Even assuming a best-case scenario for anti-skating compensation perfectly applied (200 milligrams constant plus half of 200 milligrams modulational), the uncorrectable skating force will be 100 milligrams modulational. That doesn't look good compared to one eighth of 50 = 6 milligrams. And it is present on all records, not just poorly centred ones. Therefore, any performance effect of lateral stylus forces in a linear tracking arm will also be present in pivot arms, but more strongly.


IMHO it looks like this claimed weakness of linear tracking arms has been misconceived, and it actually belongs with pivot arms. If at all. Maybe we should just 'forget' it.

What do you think? (I was pleased to read above that you don't bite )
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Old 6th June 2013, 11:31 PM   #512
directdriver is offline directdriver  United States
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Quote:
Originally Posted by tnargs View Post
This is on an arm weighing three hundred grams! A typical Airtangent-type has maybe one eighth of this sliding mass. How significant is one eighth of 'insignificant'? And that is only with poorly centred records.
Here's the full quote:
Quote:
TESTING AND MEASUREMENTS:

The objective was to get the horizontal plane arm resonance down to 2-3 Hz. The arm and carriage weigh 160 grams altogether, which was increased up to a total of 300 grams with two triangular lead weights. These were molded in the bottom of a leftover angle profile. This yielded the desired results. See measurements (Arm Graphs).

Now one might fear that poorly centered records would provoke the stylus too much when it has to move so much 'baggage'. In the old days - in the age of radial arms - there was something called a 'skateometer'. It came from Dual and could be fitted instead of the cartridge so that one could see if it had been properly adjusted. With this fitted on a tangential arm, the effect of excentric records could be evaluated. On the arms described here, the load was typically around +/- 50 milligrams. This is insignificant compared to a normal tracking force of 1.8 grams. More critical is the adjustment of the arm base to perfect level. But here is yet another advantage of this design. Simply lift the arm tube off the carriage and see if the carriage remains still.


I notice he's talking about skating force. A linear arm by nature has little or no skating force due to no offset angle and overhang, unlike a conventional pivot arm. But is this the same force as horizontal effective mass? If you use your finger to push the entire arm assembly on an airbearing or linear bearing tonearm to the record center, let say the vertical force is zero, will this lateral force be "50 milligrams"?

By the way, is horizontal resonance at 2-3Hz a little too low for warp records?

I've never owned an airbearing arm but I have friends who have and they noticed the cantilever is skewed to one side after long term use.


Quote:
Originally Posted by tnargs View Post
IMHO it looks like this claimed weakness of linear tracking arms has been misconceived, and it actually belongs with pivot arms. If at all. Maybe we should just 'forget' it.
Hmm.... I wonder why the Trans-Fi arm, a descendent of the Ladegaard design, or other airbearing arms, continues to decrease the mass of its armwand....

Where's Mark Kelly when we need him?!
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Old 6th June 2013, 11:53 PM   #513
Esperado is offline Esperado  France
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Quote:
Originally Posted by directdriver View Post
Produced in the 1960s (I think), the Transcriptor Transcriber moved the platter-bearing-motor on rails while the tonearm remained still (sort of).
According to Transcriptor's website, the Transcriber was produced between 1977-1981.
I patented this concept (moving plate and still tangential arm) for the French company i was working for (Scientelec) in 1970.
As the inertia of the plate is huge, and it can be suspended, you can get a nice filtering of the noise generated by the rotating screw used to move the plate.
http://www.esperado.fr/creations_aud...as_radial.html

Last edited by Esperado; 7th June 2013 at 12:02 AM.
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Old 7th June 2013, 01:08 AM   #514
phivates is offline phivates  United States
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The stylus still has to get from one place to another. So I wonder why the brush is not appreciated for pitching in on that task. It also introduces drag which should help with speed regularity on belt drive and direct drive units, no? Besides, the lead-in groove throws the stylus/cartridge/arm toward the center so doesn't inertia take care of skating??
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Old 7th June 2013, 01:31 AM   #515
tnargs is offline tnargs  Australia
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Hi dd
Quote:
Originally Posted by directdriver View Post
Here's the full quote:
I omitted the bit about the skateometer because it was irrelevant -- and confusing -- as it turned out to be.

Quote:
I notice he's talking about skating force.
No, he is talking about the lateral forces imposed on the stylus by an offset hole in the LP. He simply used an instrument that was intended to measure skating force to measure the 'offset hole force'. That doesn't make it skating force just because we use a skating force measurement instrument to measure a different force.

Quote:
A linear arm by nature has little or no skating force due to no offset angle and overhang, unlike a conventional pivot arm. But is this the same force as horizontal effective mass? If you use your finger to push the entire arm assembly on an airbearing or linear bearing tonearm to the record center, let say the vertical force is zero, will this lateral force be "50 milligrams"?
The lateral force under discussion is not skating force and will occur for any arm type. Its magnitude is directly proportional to the horizontal effective mass of tonearm plus cartridge. The Ladegaard arm is an extreme example of high horizontal effective mass, many times that of most modern LT arms, so most LT arms will exhibit this force at a small fraction of 50 milligrams, as per the direct proportionality. Yet the designer says the force is insignificant even in the Ladegaard arm.

If you use your finger the force will be whatever force you use in your finger!

Quote:
By the way, is horizontal resonance at 2-3Hz a little too low for warp records?
Not according to Ladegaard. He's the expert. My own reading is that the offset centre oscillation is at 0.55 Hz (33 rpm) to 0.75 Hz (45 rpm), so the Ladegaard arm has a margin of 3 to 5 times.

I also notice that you mention warp records. That is a vertical error and not relevant to horizontal resonance. Ladegaard's arm has 10-16 Hz vertical resonance to deal with warps.

The ability to independently tune H and V resonances is a huge advantage of the LT arm over pivot arms, which Ladegaard has gleefully taken advantage of.

Quote:
I've never owned an airbearing arm but I have friends who have and they noticed the cantilever is skewed to one side after long term use.
Well, something is wrong with their implementation or application or execution of their individual tonearms. Maybe their air pressure is so low the slide drags on the rail, or so high the air exhausts asymmetrically. Or some impurity has lodged between the slide and its rail and needs to be cleaned out. Or the rail is not quite level. Or it's a diy arm and the slide is dragging on the rail due to tolerances.

But one thing it is NOT due to, is the offset centre force I discussed in my previous post, as this is sinusoidal with an average of zero, so it will never twist a stylus to one side.

And it is NOT due to the force needed to 'drag' the arm towards the spindle. In fact if we want to get technical, for an air bearing LT arm with none of the issues covered above, this force is exactly zero. Well, it would be if the groove width was constant. Variations in groove width are so small that, if you want me to work out numbers for the force generated, I will estimate right now they will be ' orders of magnitude smaller than insignificant'.

Quote:
Hmm.... I wonder why the Trans-Fi arm, a descendent of the Ladegaard design, or other airbearing arms, continues to decrease the mass of its armwand....
Well, that will increase the vertical resonant frequency. Horizontal is another matter: if they want to, they can decrease arm wand weight and increase sliding carriage weight so the vertical resonant frequency is increased but not the horizontal.

Quote:
Where's Mark Kelly when we need him?!
Well you've got me, so all is well. <strictly joking!!>


Is anyone starting to appreciate my suggestion that the arguments against LT arms related to high horizontal mass are a 'common misconception'?
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Old 7th June 2013, 02:51 AM   #516
tnargs is offline tnargs  Australia
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Sorry dd, I misunderstood your 'finger' question. But I did answer it in my 'if we want to get technical' paragraph.

The air bearing arm is 'floating in space' so, like a space craft, once it is given a nudge to get started, no further force is needed if we consider the bearing to be frictionless.

The 50 milligrams force is not this force, it is the force to move the linear tracking Ladegaard arm back and forth as an offset record hole causes the vinyl groove to oscillate. Ladegaard would have measured this using a badly offset example LP, so for a good LP it might be one fifth of this, let's say 10 milligrams. And since most LT arms are about one eighth of the horizontal mass of Ladegaard's, divide 10 by 8 and whoops, we are down to 1 milligram on most records. Truly insignificant compared to the 1800 milligrams of vertical force on the stylus, and also insignificant compared to the 100-200 milligrams of uncorrectable radial skating force on all records with a pivot arm.
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Old 7th June 2013, 04:05 AM   #517
tnargs is offline tnargs  Australia
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Quote:
Originally Posted by phivates View Post
The stylus still has to get from one place to another. So I wonder why the brush is not appreciated for pitching in on that task.
Hi, I think I covered this in post #509? Shure say the sound quality is less with the brush. And the lateral stylus forces in a good LT arm are insignificant.

Quote:
It also introduces drag which should help with speed regularity on belt drive and direct drive units, no?
I agree, but it's a different topic I suppose.

Quote:
Besides, the lead-in groove throws the stylus/cartridge/arm toward the center so doesn't inertia take care of skating??
What skating? Are you talking about pivot arms?

I can't think of any form of inertia that would cancel out skating ---- could you explain this a different way for my slow brain please?
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Old 7th June 2013, 05:48 PM   #518
directdriver is offline directdriver  United States
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Default Burne-Jones

More pictures of one of the grand daddies of tangential pivot arms from this site.

I would prefer to make the vertical pivot close to the headshell area like the Dynavector split-plane design.



















































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Last edited by directdriver; 7th June 2013 at 05:51 PM.
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Old 7th June 2013, 06:05 PM   #519
directdriver is offline directdriver  United States
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Default Burne-Jones

More pix.


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Last edited by directdriver; 7th June 2013 at 06:14 PM.
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Old 7th June 2013, 06:56 PM   #520
sq225917 is offline sq225917  United Kingdom
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Surely that still has tracking angle error at either end, much less, but some none the less.
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