[Wayner]

JaS (vinylengine),

This morning with fresh eyes and brain (whats left) I see the difference from your numbers for the Technics, you must maintain the overhang from Baerwald's and that number is 18.173. That makes the OAL of (+215) =  233.173.



Wayner 

[vinylengine]

This morning with fresh eyes and brain (whats left) I see the difference from your numbers for the Technics, you must maintain the overhang from Baerwald's and that number is 18.173. That makes the OAL of (+215) =  233.173

I had to sleep on it myself, but now I definitely think the problem is the 18.173 overhang I'm guessing you used John Ellison's spreadsheet to calculate the overhang figure from a mounting distance, but his spreadsheet only allows the input of effective length, overhang and offset, or effective length, inner groove and outer groove*. I just tried putting 215mm into the 'mounting distance' box and got the 18.173 in your diagram, but it's wrong!

I use a tool Yosh sent me years ago and just checked my effective length figure for a 215mm tonearm with John's spreadsheet and it produced zero nulls at 66 and 120.9mm as expected.



Loefgren B gives even lower overall error but pushes the stylus even further forward to 18.322mm



Try inputting these figures into the L/H columns of a clean version of the spreadsheet

Cell A: 232.817 mm (effective length)
Cell B: 17.817 mm (overhang)
Cell C: 23.664 degrees (offset angle)

I'm also confident that if you plug those figures into your CAD plot that you'll get the right nulls, but I've never checked myself so it would be interesting to see what you get!

Regards,
JaS

* OK, the spreadsheet does allow you to input the mounting distance and other figures but it will mess up the calculations. These fields should really be locked

[vinylengine]

Hi,
I should have thought of this before but you can quickly generate the Baerwald overhang/offset dimensions for any mounting distance using Conrad Hoffman's excellent Arc Protractor Generator

Just input the mounting distance, choose IEC null points and press 'print protractor' to bring up a confirmation box with the figures. You can double check the figures by inputting the effective length into John Ellison's spreadsheet

Regards,
JaS

[gjs_cds]

The tonearm is made from wood and is 60cm long! The Horo WJE 168, according to designer Luigi Pasqualini (shown), was designed as a "musical instrument" would be. The price has not yet been announced.

Wouldn't that produce awful results, as the sound reproduction would be contaminated by the resonating frequency/characteristics of the tone-arm?

[Wayner]

Ah, here is the problem. You have to strike the arc using Baerwald's spindle to tonearm pivot center. Any alignment jig that references Baerwald's 2 null points, start with the 210.427mm spacing. You just can't change that number to any distance you want. That is the number the null points are drawn from.

So I could draw your different overhang number, but not from the 215mm distance of the Technics. That would be like digging up your house and moving it over 2 feet.

That, my friend is the whole purpose of this thread. You can't do what you just told me to do.

Wayner 

[BobM]

Hi,
I should have thought of this before but you can quickly generate the Baerwald overhang/offset dimensions for any mounting distance using Conrad Hoffman's excellent Arc Protractor Generator
Regards,
JaS

I just downloaded and printed the 3 arcs that are covered: Stevenson A, Lofgren A and Lofgren B. Each has its own and different overhangs and null points. Which one would provide the least tracking error?

[acwd1950]

Wayner and JaS,
Couple of questions, first where do you find these specs. for a turntable? Mines a Dual 1242. Second does the overhang change if you change cartridge from a factory one to a aftermarket one? I have been thinking about this and did some research on tonearms. If the headshell pivoted at the headshell and was held perpendicular to the groove across the whole record it would eliminate all of that? There was a company that made these type of arm in the fifties and I have seen this design somewhere else but cant put my finger on it.

Steve

[rcag_ils]

I do get a kick out of reading all these posts. The fact of the matter is there's really hard to get the two ideal null points. To get the so called "two ideal null points", you will have to mount, and remount the arm many times, re adjust the cartridge all day long until the wire clips break off the wires, then reset the counter weight thousands of times, then still may not get your "two ideal null points".

Just get one good null points, then get the second null point as close as you can, then call it the day.

[Wayner]

Here is the geometry for the Technics with the new overhang....Not to bad! but the angles are not the same. And they never will be.



I have not played around with the numbers for the Technics, and I'm sure with some time I would have came up with some numbers to would get a real good looking distortion and tracking curve.

However, this also presents a real problem to the user. Most 2 point alignment jigs do not have a way for the user to set a different overhang other then what the manufacturer has supplied. Technics has a jig that puts the cartridge at 15mm overhang. How is the ordinary guy suppose to figure out without a CAD or other devices, where the extra 3.whatever mm is suppose to be?

Geometrically I think I have proven my point. And while some turntable arm combinations may come close, some will not.

My approach to the problem is to keep the manufacturer's overhang distance (or close to it) and fool around with the offset angle.

The set-up process should be find correct stylus overhang, then dial in correct offset angle and have the ability to repeat both, repeatedly.

Using 2 points with cross-hairs (as most alignment card have) make's me really question the accuracy of them. We are talking about using the process of parallexing to points to not only set overhang, but offset as well.

acwd1950,

The arms you talk about are called linear tracking tonearms. While the idea sounds great for the home audio guy, the cost of preventing tracking errors with this type of arm really is prohibitive. Clear Audio has one for about 10G if you want one.

rcag_ils,

I agree, I am looking for the simplest process that everyone can use and figure out. However, the math, the geometry should be correct. Personally I don't care which perimeters are  used. You can have null points anywhere on the record surface. It's just all a matter of geometry. And lowest distortion.

Wayner 

[jrtrent]

My approach to the problem is to keep the manufacturer's overhang distance (or close to it) and fool around with the offset angle.

Very interesting thread, and admittedly over my head.  I use a one-point protractor (GEO-DISC) so don't have much experience with two-point (except with my Well Tempered, but it cheats by also having a ring around the spindle whereby you set overhang directly).

I had thought, however, that the universal two-point protractors didn't worry about the turntable manufacturers' recommended overhang (such as the 15mm specified by Technics), but let you go back and forth between the two null points til you achieved proper overhang and offset angle for the alignment scheme you had chosen.  Whether that matches the manufacturer's suggested overhang or not shouldn't effect the results in terms of minimizing tracking angle error, should it?

acwd1950,

The arms you talk about are called linear tracking tonearms. While the idea sounds great for the home audio guy, the cost of preventing tracking errors with this type of arm really is prohibitive. Clear Audio has one for about 10G if you want one.
Wayner 

He might be referring to the articulated arms used by Garrard in models  like the Zero 100 and GT-55.

[vinylengine]

Ah, here is the problem. You have to strike the arc using Baerwald's spindle to tonearm pivot center. Any alignment jig that references Baerwald's 2 null points, start with the 210.427mm spacing. You just can't change that number to any distance you want. That is the number the null points are drawn from.

Seriously, I'm not sure where you got this from? It's new to me. If you read Loefgren/Baerwald papers you'll find they didn't specify a spindle to pivot distance, they didn't even specify null points. What they did do is develop an equation that gives you the equal error at the inner, centre and outer groove (Loefgren A) or lowest overall error between the inner and outer grooves (Loefgren B) for any chosen inner and outer groove dimensions.

In the case of IEC standard grooves you end up with null points at approx 66.0 and 120.9mm for Loefgren A and it is these figures that most two-point protractors are designed to. These null points apply to any length tonearm and there is only one overhang/offset distance at which this will align for any single mounting distance.

So I could draw your different overhang number, but not from the 215mm distance of the Technics. That would be like digging up your house and moving it over 2 feet.

The overhang figure is the correct overhang for a 215mm arm according to Loefgren's A alignment. If you feed this back into John Ellisons spreadsheet you will get agreement - unfortunately you can't do it the other way around as the mounting distance box in his spreadsheet isn't an input field. It's not a problem with the geometry or the spreadsheet, it's just not designed for this purpose. Luckily Conrad Hoffman's arc generator makes it easy to reverse engineer the correct figure for any mounting distance.

I'm actually quite happy with your new drawing as it clearly shows that if you move the cartridge forward and change the offset angle according to Loegren's equation you can align at both points. There's a 0.017 degree difference in the measured offset angles but I'm guessing that if you used more precision in the equation to begin with (maybe 5-6 decimal places?) it would be even closer. It doesn't really matter as you're actually aligning to the null points themselves and are unlikely to be able to align to this sort of precision. 99% of alternative null points (including most manufacturers) will technically perform worse. If anything your drawing and the figures from John's spreadsheet support the use of Baerwald or Loefgren B null points where you have the room in the headshell to align to them

Regards,
JaS

[vinylengine]

I just downloaded and printed the 3 arcs that are covered: Stevenson A, Lofgren A and Lofgren B. Each has its own and different overhangs and null points. Which one would provide the least tracking error?

Basically they are designed to provide different spreads of distortion.

Loefgren A (also known as Baerwald) will give you the lowest possible amount of tracking error at the inner, centre and outer grooves while keeping this error equal at all 3 points. There is a gentle rise and fall in error between these points.

Loefgren B, as recommended by Feickert, will give the lowest overall tracking error of any alignment method but with slightly higher error at the beginning and end of the record than the A method. You will also need another 1mm or so in your headshell length.

Stevenson is a later variation on Loefgren A, but he fixed the inner null point at the inner groove position as he considered this to be the most important point for low distortion.

If you plot the 3 on a graph you can see that they perform differently across the record, with Stevenson giving markedly higher distortion across the record for quite a small reduction of error close to the inner groove. As most records don't even run as far as this theoretical inner groove limit it's hard to justify using it unless your headshell is too short to align to the other alignments

In theory you could measure the inner groove diameters of your records and use the average figure to modify the Arc to optimise it for your collection, but any improvement is likely to be small

Regards,
JaS

[vinylengine]

I use a one-point protractor (GEO-DISC) so don't have much experience with two-point (except with my Well Tempered, but it cheats by also having a ring around the spindle whereby you set overhang directly).

FWIW the Geodisc aligns to Baerwald IEC null points. You can double check with any two-point protractor with the null points at 66 and 120.9mm (eg Ortofon, Turntable basics etc). Any difference will be down to how well you managed to sight the pivot point and how accurately the protractors are printed/etched

Regards,
JaS

[jrtrent]

FWIW the Geodisc aligns to Baerwald IEC null points. You can double check with any two-point protractor with the null points at 66 and 120.9mm (eg Ortofon, Turntable basics etc). Any difference will be down to how well you managed to sight the pivot point and how accurately the protractors are printed/etched

Thanks for that information.  Double-checking with a 2-point protractor is probably not a bad idea; sighting it in can get more difficult with the passing decades.  To my ears the Geodisc has worked well since first getting one in 1985.  It's been mostly used with my LP12 (and it was the Linn dealer who recommended and sold me the Geodisc) and now more recently with my WTRP.  Stanalog had said Baerwald alignment would work just fine; their own protractor might be closer to Stevenson as it uses less overhang and reduced offset angle.  Both alignment methods sound equally good to me.

[Wayner]

Ah, here is the problem. You have to strike the arc using Baerwald's spindle to tonearm pivot center. Any alignment jig that references Baerwald's 2 null points, start with the 210.427mm spacing. You just can't change that number to any distance you want. That is the number the null points are drawn from.

Seriously, I'm not sure where you got this from? It's new to me. If you read Loefgren/Baerwald papers you'll find they didn't specify a spindle to pivot distance, they didn't even specify null points. What they did do is develop an equation that gives you the equal error at the inner, centre and outer groove (Loefgren A) or lowest overall error between the inner and outer grooves (Loefgren B) for any chosen inner and outer groove dimensions.

In the case of IEC standard grooves you end up with null points at approx 66.0 and 120.9mm for Loefgren A and it is these figures that most two-point protractors are designed to. These null points apply to any length tonearm and there is only one overhang/offset distance at which this will align for any single mounting distance.

So I could draw your different overhang number, but not from the 215mm distance of the Technics. That would be like digging up your house and moving it over 2 feet.

You have just proven that you do not understand the geometry behind where the null points come from.

They are tangential locations, period. It's based on geometrical position of the tonearm's pivot center in realationship to the platter spindle. There is nothing magical about geometry.

I have proven to you with example after example, that the theory of 2 null points by any one of the guys you mentioned does not work for many turntable/arm combinations. It is impossible, if they don't share the same arm specifications!

When you find out how 2 arc from different centerpoints can share the same properties and location, let me know.

W

[Wayner]

Also, the entire subject we are discussing happened because a bunch of dudes knew (back then) that there was a geometrical problem running a pivoting point tonearm thru a record groove cut in a linear fashion. That is why they developed their points based on specific geometry of the arm specifications that they deemed the best possible out of all the infinite design considerations. Without considering arm geometry there are no null points, alas the linear tracking tone arm has no null points.

W

[vinylengine]

You have just proven that you do not understand the geometry behind where the null points come from

I do have a basic understanding of the geometry proposed by Loefgren - I even helped a little in the first English translation of the document that you will find on my site. While I'm not a mathematician I'm always open to new ideas and if you can explain what you mean by 'Any alignment jig that references Baerwald's 2 null points, start with the 210.427mm spacing' I'd appreciate it as I've never come across this before? I'm pretty certain this isn't in any of his papers but I could be wrong?

From bkearns 'treatise on cartridge alignment' here are the basic equations you need to calculate the required parameters for overhang and offset angle once you've chosen the null radii:

Le = effective length
Lm = mounting distance
N1 = inner null radius
N2 = outer null radius
Oh = overhang

Effective length

Le^2 = Lm^2 + N1*N2

Offset angle

Sin(theta) = (N1+N2)/(2*Le)

Overhang (If you know the mounting distance):

Oh = Le-sqrt(Le^2-N1*N2)

I have proven to you with example after example, that the theory of 2 null points by any one of the guys you mentioned does not work for many turntable/arm combinations

To be fair only one of your examples used Loefgren alignment, the one where I provided the correct figures for overhang and offset angle, and the error in measured offset angle was negligible.

The examples where you showed arms not hitting null points when they hadn't had the overhang/offset angle readjusted aren't surprising - the arms where aligned for different null points by the manufacturer!

When you find out how 2 arc from different centerpoints can share the same properties and location, let me know

Firstly it's not the same arc as the manufacturer as you've changed the effective length, secondly the offset angle are different for each effective length so that you still have tangency at the same null points.

Also, you still seem to be implying that each and every mounting distance has a unique set of perfect null points? If this is the case then it's an important discovery because it undermines 70 years of arm geometry theory as all the main theories since then (Baerwald 1941, Seagrave 1956, Stevenson 1966 etc) are based on the equations in Loefgren's 1938 paper.

For arguments sake, and to further my understanding, let's presume there are only one set of perfect null points for any mounting distance. How do you go about calculating them? You can't rely on manufacturers data as they don't agree 

For example here are some manufacturers null points for arms mounted at 222mm:

Audiocraft: 60.0 / 114.7

Azden: 61.2 / 112.5

Clearaudio: 66.0 / 121.0

Grace: 66.8 / 103.0

Acos: 60.3 / 114.2

Micro Seiki: 66.8 / 103.0

Rega: 60.0 / 114.7

Schroder: 65.9 / 121.1

SME: 66.0 / 120.8

Sony: 60.3 / 114.2

Each of these manufacturers chose different overhang and offset angles that resulted in these alignments - mounting distances are identical. But which is correct?

As I read it there are a multitude of different variations in null points available by the simple expedient of altering the overhang (and therefore the effective length) and the offset angle. This can be done easily at the design stage, or if you can move the cartridge enough in the headshell you have some choice as an end user.

To align to IEC null points calculated from Loefgren's equation (66 and 120.9) all you have to change the overhang and offset angle. As long as you have the room in the headshell I don't see the problem 

Without considering arm geometry there are no null points, alas the linear tracking tone arm has no null points.

I'm being a bit picky but Linear tracking arms could be said to have an infinite number of null points 

Regards,
JaS

[Wayner]

My very first post has a CAD drawing for Baerwald's "perfect tonearm". I'd like to stay with him because all of the others just confuses the issue. Baerwalds numbers are not wrong. For his "perfect arm specifications of:

Tone arm pivot to spindle center of 210.427mm

Overhang is then 18.173mm

Offset angle is then 24.128mm

It gave him a total harmonic and tracking distortion that was the lowest he thought possible. All of these guys just picked slightly different variables ( happening thru a period of years) and they all extrapolated on each other's work.

Drawn on the CAD, the  numbers work perfectly (with a error of a couple of thousandth of a degree) as most of these guys used a slide rule for their calculations. It worked perfectly. Any of the examples you gave me failed.

There is no fairy dust or foo-foo magic involved at all.

Yes, many manufacturers have their own null points. They thought that their geometry was better for what ever reason. The object of the whole exercise was to produce an arm specification that produced the best tracking with the least amount of distortion and wear.

I think you are confused on which came first, the chicken or the egg.

The resulting null point specifications are the result of tone arm specifaction investigations. What if you decided to have a 7" long tone arm? it would be a disaster.

I believe all of these guys did thousands of calculations trying to find the best tone arm specs considering the situation.

As far as the linear tracking tonearm, the entire length of the record is it's null point.

W

[rcag_ils]

FWIW the Geodisc aligns to Baerwald IEC null points. You can double check with any two-point protractor with the null points at 66 and 120.9mm (eg Ortofon, Turntable basics etc). Any difference will be down to how well you managed to sight the pivot point and how accurately the protractors are printed/etched

That's pricisely what I've been doing after trying to adjust the cartridge for the "two ideal null points" unsucessfully, wasted a lot of time, and broke a few cartridge wire clips.

I aligned the cartridge with the Geo-Disc, recheck it with the two point protractor that I printed off "enjoy the music". They come very, very close, good enough for me.

Also most stylus are not cut to the same shape as the record cutting stylus, so you'd have to get something like an Ortofon if you want precise reproduction.

[vinylengine]

My very first post has a CAD drawing for Baerwald's "perfect tonearm". I'd like to stay with him because all of the others just confuses the issue.

OK, let's keep it simple. Can you point me to the document where Baerwald recommends an arm of 210.427mm mounting distance? I've got Baerwald's paper in front of me but it's 30+ pages long of equations and explanations but I don't see this figure (his paper uses imperial measurements)  It seems very odd as longer arms produce lower tracing error - punch a longer effective length into the spreadsheet and the maximum and average distortion figures go down. Of course if it's not possible to achieve this alignment at longer effective lengths this is academic.

Also are you saying that this is the only mounting distance from which you can align to points calculated using Baerwald's equations?

Regards,
JaS