View Full Version : Different length tonearm why ?
HI all
Please excuse the silly question but I always wondered what the thinking is behind longer than normal tonearm
Most are 9 inches but a few I have seen are 10 and 12 inches, what is the reason or thinking behind these longer arms.
Thanks for any input in clearing up my confusion on this subject.
Paul
The 9" length is largely historic. Clearly tonearms must be longer than the nominal radius of the 12" LP, so a length of 1.5 times that distance was somewhat arbitarily chosen.
There were at the same time 16" diameter LPs, so to play them a 12" long arm was used. (For example, the EMT927 turntable has a large enough platter to play 16" records, and is equipped with a 12" arm (305mm).)
Obviously longer arms can be used with turntables having a smaller diameter platter, but there are trade-offs: longer arms will display lower tracking distortion, but have higher effective mass, whereas shorter arms will have higher tracking distortion but lower mass.
Not all arms are 9" long, several 10" and 10.5" arms are available, and some believe this length is close to optimum and thus preferred.
Firebottle
24-04-2017, 06:19
Good post Barry :)
9 inches is enough for anyone
The best path across a record is a straight line, with zero deviation for the stylus contact angle.
A longer tone arm has a bigger tracking radius than a short one and therefore less deviation from the ideal path.
Unfortunately going too long also has other purely physical obstacles when trying to achieve a good design, otherwise 3 foot arms would be in use.
Simplistic explanation I know, but it was a simple question and deserves a simple answer. :)
Ali Tait
24-04-2017, 07:24
Use a parallel tracker instead. :-)
Use a parallel tracker instead. :-)
Now there's a thought! :D
alcarmichael
24-04-2017, 09:46
The best path across a record is a straight line, with zero deviation for the stylus contact angle.
A longer tone arm has a bigger tracking radius than a short one and therefore less deviation from the ideal path.
Unfortunately going too long also has other purely physical obstacles when trying to achieve a good design, otherwise 3 foot arms would be in use.
Simplistic explanation I know, but it was a simple question and deserves a simple answer. :)
This 'less deviation from the ideal path' means that a longer arm would be less susceptible to distortion on the inner grooves of a record yes?
montesquieu
24-04-2017, 10:25
This 'less deviation from the ideal path' means that a longer arm would be less susceptible to distortion on the inner grooves of a record yes?
Yes.
12 inch arms in general are also well-suited for low compliance cartridges which work better with a high mass arm. (Though to complicate things, not all 12in arms are higher mass than a heavyweight 9 incher like a Fidelity Research FR64S or my own Ikeda IT-345 CR1).
The OP's question is actually an opener to the whole topic of arm geometry, overhang, mass, cartridge compliance, resonance and so on.
Yes, less distortion at the start and end and in the middle.
The only two positions on the tracking arc where the stylus is exactly parallel (tangential) with the grooves is at the two null points, everywhere else there is a small discrepancy.
If you consider it as the overhang, before the first(outer) null point the overhang is shorter than ideal.
Between the outer and inner null points it is longer than ideal and after the inner null point it is again shorter.
The amount it is out is directly proportional to the length of the arm, longer is less adrift.
The points about mass etc raised earlier, are valid, so its not all plain sailing by just using a longer arm, so as with most things, you have to decide where you want to compromise.
I used to have problems with inner groove distortion, that just wouldn't go away, no matter which alignment scheme I used, which is why I now use a linear tracker.
Are you bringing your turntable to NEBO, Ken?
Edit (later) ... I see from the NEBO thread, that you are ... excellent!
Peter - Yes, as you spotted.
My Denon DL-301 mkII crapped out, when the cantilever just fell out.
So I am using a pre owned Ortofon MC20 Supreme at present, nice cartridge.
To be played through a Pro-Ject Phono Box RS/Pre Box RS, my semi active crossovers/Nakamichi Power Amp and three way speakers.
The later is all a work in progress, but sounding pretty damn good for a lash up. ;)
paulf-2007
24-04-2017, 16:03
Yes.
12 inch arms in general are also well-suited for low compliance cartridges which work better with a high mass arm. (Though to complicate things, not all 12in arms are higher mass than a heavyweight 9 incher like a Fidelity Research FR64S or my own Ikeda IT-345 CR1).
The OP's question is actually an opener to the whole topic of arm geometry, overhang, mass, cartridge compliance, resonance and so on.my Stax 12" is obviously not high mass as the Shure ultra 500 sounds great. I also have a Stax 9" arm but haven't got around to using it yet.
montesquieu
24-04-2017, 16:05
my Stax 12" is obviously not high mass as the Shure ultra 500 sounds great. I also have a Stax 9" arm but haven't got around to using it yet.
The stax arms are most definitely a case in point being from the high compliance, low arm mass era.
CornishPasty
24-04-2017, 19:21
Imo most turntables come with a nine inch arm to keep the footprint down to a reasonable size.
Use a parallel tracker instead. :-)
Whilst conceptually an elegant solution the actual mechanics involved in realising this solution are riddled with issues that introduce compromises that are very difficult to overcome and end up being very complex.
alcarmichael
25-04-2017, 06:24
Whilst conceptually an elegant solution the actual mechanics involved in realising this solution are riddled with issues that introduce compromises that are very difficult to overcome and end up being very complex.
Would you please expand? As lately I have been considering this option...
Would you please expand? As lately I have been considering this option...
Be interested in the thinking myself.
Records are cut using a linear tracker, using a pivoting arm, actually introduces more complications and issues to overcome.
Ammonite Audio
25-04-2017, 09:21
Be interested in the thinking myself.
Records are cut using a linear tracker, using a pivoting arm, actually introduces more complications and issues to overcome.
Parallel trackers are fine in theory, but invariably involve more complications and issues than a pivoted arm. I am yet to hear a parallel tracker that was actually a good tonearm, so for me it's a question of balancing the various technical compromises and those are far easier to reconcile with a pivoted arm.
Here's an interesting take on the issue - a pivoted tonearm that tracks like a parallel tracker, without any articulating linkages in the armtube or headshell:
http://www.reed.lt/components/com_virtuemart/shop_image/product/5t-virtuemartgallery-001.jpg
Parallel trackers are fine in theory, but invariably involve more complications and issues than a pivoted arm. I am yet to hear a parallel tracker that was actually a good tonearm, so for me it's a question of balancing the various technical compromises and those are far easier to reconcile with a pivoted arm.
I hear this often, but no one will define what the complications or issues are.
A parallel tracker has far fewer issues to overcome in my opinion.
The whole null point compromise, bearing friction and anti skate requirement of a pivoting arm, don't exist on an air bearing linear tracker.
Low end pivoting arms are cheap to produce and that's about it. By the time you get to a decent quality pivoting arm, there is little difference in cost between the types.
The engineering principles of my linear tracker are far simpler than your average pivoting arm.
http://www.trans-fi.com/terminatortonearm.htm
Pivoted tonearms and linear tracking tonearms each have their own set of compromises - neither are perfect.
Ammonite Audio
25-04-2017, 12:53
Exactly!
Again, what specific compromise, give me one thing to work with. :scratch:
I can and have, named some compromises, that have to be made on a pivoting arms.
None of these apply to the linear tracker I linked to, so what is the trade off with that design?
You can't argue with generalisations. :)
killie99
25-04-2017, 13:44
Here's summary of problems with linear trackers http://forums.stevehoffman.tv/threads/linear-tracking-tonearms-are-they-worth-it.75901/
Here's summary of problems with linear trackers http://forums.stevehoffman.tv/threads/linear-tracking-tonearms-are-they-worth-it.75901/
Comments made in 2006, not much relating to the design I linked to?
It names the same things I did, as design issues for a pivoting arm.
Other than saying an air bearing is superior to a ball race. The only criticism seems to be "what if the air pump packs in"
The vertical/horizontal mass is not an issue on my linked design as it is the reverse situation to what is suggested and the comments were probably referring to a specific type of design, so would be relevant in that case, and several older designs.
There are always going to be differences in individual designs, for both types and I'm not promoting one generic type as better sounding than the other, there will be good and bad for both.
But there is less compromise in a linear design, it is a more elegant engineering solution and I would say the article almost favours linear.
I wouldn't dispute the fact that your Terminator is a good tonearm, but it is not without compromises:
Dissimilar effective mass in the horizontal and vertical plane, leading to dissimilar cartridge-arm resonant frequencies,
Short arm wand length exacerbates warp-wow, and scrub-flutter effects,
Long length of unshielded cartridge wiring used,
Noise of the pump and of the air issuing from the bearing.
I wouldn't dispute the fact that your Terminator is a good tonearm, but it is not without compromises:
1.Dissimilar effective mass in the horizontal and vertical plane, leading to dissimilar cartridge-arm resonant frequencies,
2.Short arm wand length exacerbates warp-wow, and scrub-flutter effects,
3.Long length of unshielded cartridge wiring used,
4.Noise of the pump and of the air issuing from the bearing.
Like you say all designs have issues and compromises.
On your points, I would comment as follows.
1. I don't know how this can be translated into audible effects, is dissimilar effective mass a major problem. The arm is less prone to cartridge matching issues due to compliance than most, it seems to work with a very wide range.
2. So if the record is poor (warp) it is likely to sound bad. Never heard the term scrub-flutter. In practice, many say with this design the shorter the better and they back the cartridge right up the slots. Can't vouch for that myself.
3. Has no audible effect in my set up with 700mm length cable. If it was a problem I could always use the balanced cable option, or short cable to Phono/Coax, much the same as conversional tone arm cable, then coax. So applies to both arm types really.
4. No noise from the pump as its in the next room. I can't hear any air from the bearing at 300mm with the system muted.
I think the post has been off topic for long enough, sorry to the OP for the deviation.
paulf-2007
25-04-2017, 22:35
The transfi linear tracker is somewhat ugly and lack of dimensions put me off as I couldn't tell if it would fit my turntable.
As a rough comparison I heard a 301 with air bearing arm and ortofon A90 cart against a collaro 2010 with Diy 12" oak unipivot with Benz micro gold belonging to me at the time and the owner of the 301 said he couldn't really say which was better but if pushed said maybe the Ortofon A90 just had the edge, at £3500 I would hope it would. The air bearing arm was set up optimally before you get started on that. I've always fancied a clearaudio linear arm but couldn't run to that kind of silly money.
1. I don't know how this can be translated into audible effects, is dissimilar effective mass a major problem. The arm is less prone to cartridge matching issues due to compliance than most, it seems to work with a very wide range.
It is the grossly dissimilar effective masses in the vertical and horizontal planes that most troubles me.
Let us take the case of a typical cartridge: the Denon 103. This has a mass of 8.5g. The quoted compliance (at 100Hz) is 5 10-6 cm/dyne, so at ~ 10Hz it is 7.5 – 10. 10-6 cm/dyne. With a quoted arm effective mass of 80g in the horizontal plane, the (calculated) cartridge/arm resonance will lay between 5.3 – 6.2Hz, which is low enough to show up problems with foot falls unless the deck is very well isolated from the floor. In the vertical plane, with a quoted arm effective mass of 3g, the cartridge/arm resonance will lay between 14.8 – 17.1Hz, which might cause any resonance to intrude into and effect the low frequency response of the system.
The situation is worse with Decca cartridges, which themselves have dissimilar compliance figures in the horzontal and vertical planes. Typical figures quoted by Decca are 12.10-6 dyne/cm in the horizontal plane and 5.10-6 cm/dyne in the vertical plane. The mass of a Decca Mk.V or Mk. VI is 5.8g, so in the horizontal plane the cartridge arm resonance will lay in the region 4.9 – 6.3Hz. Likewise the cartridge/ arm resonance in the vertical plane will lay in the region 24 – 28Hz. The latter, unless very well damped, will definitely affect the low frequency response of, and possibly overload the phonostage.
2. So if the record is poor (warp) it is likely to sound bad.
Never heard the term scrub-flutter. In practice, many say with this design the shorter the better and they back the cartridge right up the slots. Can't vouch for that myself.
Scrub flutter is a term, which describes the effect of longitudinal modulation of the stylus as it rides over a warp. If the warp is severe, the cartridge will bounce up and down after the warp (in much the same way as a car can bounce up and down after riding a speed bump, if the suspension is not sufficiently well damped). The result of this damped vertical motion is to cause the cantilever to pivot about the tip and the stylus tip will move back and forth longitudinally in the groove, hence the term ‘scrub flutter’. The size of this effect depends on the severity of the warp, the mass of the cartridge and on the compliance of the cantilever suspension. It is exacerbated in arms of short length.
3. Has no audible effect in my set up with 700mm length cable. If it was a problem I could always use the balanced cable option, or short cable to Phono/Coax, much the same as conversional tone arm cable, then coax. So applies to both arm types really.
I was referring to the fine wires emerging from the cartridge carrier, not to the cables between the arm base and the phonostage. Obviously those fine wires must be sufficiently close together to be able to reject common-mode interference such as RFI and/or mains hum. Do the wires have to be ‘dressed’ so as to minimise their effect on the motion of the slide?
4. No noise from the pump as its in the next room. I can't hear any air from the bearing at 300mm with the system muted.
Fair enough – though having to place the pump in another room is a bit of an imposition. Isn’t there a pressure drop over the length of air pipe?
Clearly you experience none of these problems, and are happy with your arm, but in my opinion they are compromises.
There are a couple of features which I do like about the Terminator arm: the ability to adjust VTA/SRA easily (and whilst the record is playing?), and the ability to change arm carriers should one wish to swap cartridges quickly and easily.
Paul - Looks are a personal thing, for what its worth, I like it.
"and lack of dimensions put me off as I couldn't tell if it would fit my turntable"
I don't know how long ago your talking about, but there has been a dimensioned square on the Trans-fi Audio site for several years that I know of.
If you have a fixing hole on your TT, anywhere within the square, it will fit.
Barry - Thanks for the detailed explanation.
Further to this:
1. Different vertical/horizontal mass - Vic points out the frequencies you mention, on his site, but states that the air bearing does not respond in the text book fashion. As he's the owner and designer, I'm always going to take statements like that with a grain of salt. But it does seem to translate into real world results. There are some great independent reviews of the arm and I can't see that happening if there was a major flaw in the basic physics, it just wouldn't sound right, or good enough to be labelled giant killer, capable of going head to head with pivot arms 3 to 4 times the price. I wouldn't attempt to defend any of that, as it is way beyond my experience, but all the claims Vic makes do seem to show through. You mention Decca cartridges as a particular mismatch problem, yet Vic's cartridge of choice is a Decca Reference. As for foot fall, I had my TT at Scalford last Month, on a £5 Ikea table, in a first floor room with a creaky wooden floor and a door/closer that kept crashing shut every time someone came in. I could feel the door and foot steps through my feet all day and it never skipped or showed any kind of distortion, till I knocked the table of course, which I did a couple of times.
2. Scrub flutter - Yes I would agree that the vertical angle of lift on a short arm will be greater as it goes over a hump in the record. So the cartridge will start to complain earlier than if on a longer arm. But it will have to be a hell of a hump and my cartridge usually bottoms out on the hump before this happens.
3. Cartridge Wires - I actually use unshielded silver wire 700mm long from the cartridge tags straight to my Phono stage inputs and get zero hum. If it was a problem, the options I mentioned are available. But there is little pollution from other cables/boxes if your TT is up on top, away from the other gear. Yes, the wires need dressing to avoid drag, but that is also the case on pivoting arms, some designs are more prone than others. I very briefly owned a uni-pivot that was very twitchy in this respect.
4. Pump Pipe - It's only 3.5m away through a double brick wall so no noise, or major pressure drop. I've used the pump with 6m of tube on the lowest setting without issue, which is only about 10/15% of its full output, so plenty in reserve. Having to work around the pump noise, is a compromise, but even when installed in the listening room, the pump is drowned out by the noise from my fridge in the kitchen breaking through, as my listening position is level with the door and in line of site of the fridge, a definite compromise.
It works for me, but won't suit everyone. The set up is different, rather than harder and something you get better at with practise. A guy cornered me at Scalford and asked how I managed to set it up, he said it was so well behaved. He had tried and tried but never got his working properly and ended up selling it. After seeing mine operate, he was regretting that and wished he had persevered. After listening to how he was going about it, I wasn't surprised it wouldn't perform, he was doing his own thing and ignoring the instructions. I can set mine up from scratch with a new cartridge in 15/20min, which is quicker than I could sort my stock Technics SL-1200. I spend longer fine tuning the VTA and Phono Stage loading, but it is pretty close from the start and I can adjust both of those on the fly fairly quickly, till I find the sweet spot. :)
Just a few Terminator comments....
I've been along the T3Pro journey with Vic as the arm developed, indeed I got to beta test virtually all the developments. I've used London Super Gold, Jubilee and Reference with the arm (plus ATs, Ortofons etc). The Reference is still in place and is on its 2nd Paratrace tip so it's done some miles. I've not run an original Decca but the modern Londons work really well with the arm.
The short wand was chosen because it sounds so much better than a long wand, believe me there has been a lot of auditioning of so many different setups. Performance over warps is fine, I've no quibbles there.
As for the wiring from the cartridge; yes the wires do need to be dressed such that they don't restrict movement of the slider or be so badly placed such that they alter the VTF. This isn't rocket science and there's a simple procedure to follow. The wire I use is what that Vic used to sell, he's run out of the wire recently and can't source it again, this wire is screened - I use an unbroken run straight to my phono stage. The unscreened wire now used is good too, probably this is better used just to the phono sockets on the arm due to it being unscreened but this will be system dependent.
Theory is a good starting point but that's all it is. Analogue setups are all full of compromises so auditioning is vital; an over-reliance on theory can be very counter-productive.
montesquieu
27-04-2017, 11:53
It is the grossly dissimilar effective masses in the vertical and horizontal planes that most troubles me.
Let us take the case of a typical cartridge: the Denon 103. This has a mass of 8.5g. The quoted compliance (at 100Hz) is 5 10-6 cm/dyne, so at ~ 10Hz it is 7.5 – 10. 10-6 cm/dyne. With a quoted arm effective mass of 80g in the horizontal plane, the (calculated) cartridge/arm resonance will lay between 5.3 – 6.2Hz, which is low enough to show up problems with foot falls unless the deck is very well isolated from the floor. In the vertical plane, with a quoted arm effective mass of 3g, the cartridge/arm resonance will lay between 14.8 – 17.1Hz, which might cause any resonance to intrude into and effect the low frequency response of the system.
The situation is worse with Decca cartridges, which themselves have dissimilar compliance figures in the horzontal and vertical planes. Typical figures quoted by Decca are 12.10-6 dyne/cm in the horizontal plane and 5.10-6 cm/dyne in the vertical plane. The mass of a Decca Mk.V or Mk. VI is 5.8g, so in the horizontal plane the cartridge arm resonance will lay in the region 4.9 – 6.3Hz. Likewise the cartridge/ arm resonance in the vertical plane will lay in the region 24 – 28Hz. The latter, unless very well damped, will definitely affect the low frequency response of, and possibly overload the phonostage.
Scrub flutter is a term, which describes the effect of longitudinal modulation of the stylus as it rides over a warp. If the warp is severe, the cartridge will bounce up and down after the warp (in much the same way as a car can bounce up and down after riding a speed bump, if the suspension is not sufficiently well damped). The result of this damped vertical motion is to cause the cantilever to pivot about the tip and the stylus tip will move back and forth longitudinally in the groove, hence the term ‘scrub flutter’. The size of this effect depends on the severity of the warp, the mass of the cartridge and on the compliance of the cantilever suspension. It is exacerbated in arms of short length.
I was referring to the fine wires emerging from the cartridge carrier, not to the cables between the arm base and the phonostage. Obviously those fine wires must be sufficiently close together to be able to reject common-mode interference such as RFI and/or mains hum. Do the wires have to be ‘dressed’ so as to minimise their effect on the motion of the slide?
Fair enough – though having to place the pump in another room is a bit of an imposition. Isn’t there a pressure drop over the length of air pipe?
Clearly you experience none of these problems, and are happy with your arm, but in my opinion they are compromises.
There are a couple of features which I do like about the Terminator arm: the ability to adjust VTA/SRA easily (and whilst the record is playing?), and the ability to change arm carriers should one wish to swap cartridges quickly and easily.
I've looked into parallel trackers and rejected them for many of the reasons above. Actually with a properly set up stadard 9in arm (never mind a 12in arm) end groove distortion can be eliminated, while compliance matching is pretty transparent and the mechanisms for adjusting setup including bias, VTA and VTF are all pretty well established.
I've experimented with one of these - Nasotec swinging headshell
http://i1181.photobucket.com/albums/x440/montesquieu61/royaln-naso_zpsonmjzqqb.jpg
I've found it has some advantages - it self-aligns very nicely - but again, with a properly adjusted arm, I'm not convinced it makes more than a very slight difference in outer and inner grooves. Only really for those who are super-keen on getting these things correct (indeed the sort of believers who would go for a parallel tracker, for all their faults).
https://www.youtube.com/watch?v=vhqncpcv7ow
The single biggest problem with arms like the Terminator is the air bearing isn't constrained - in that it relies on gravity to pressurise the air film (more sophisticated designs use a pressurised sleeve or shaft moving in a sleeve. Even then, whilst this addresses some problems it's not a panacea). Air is really a very compliant bearing surface compared to others used in arms (wheels, ball races, jewel pivots etc.). The second significant issue is that the mass of the arm (not just the arm wand) is very different laterally to vertically and even a very tiny deviation from absolute level will apply significant side forces on the stylus (particularly an issue if level changes during play due to the shift of arm mass)
The single biggest problem with arms like the Terminator is the air bearing isn't constrained - in that it relies on gravity to pressurise the air film (more sophisticated designs use a pressurised sleeve or shaft moving in a sleeve. Even then, whilst this addresses some problems it's not a panacea). Air is really a very compliant bearing surface compared to others used in arms (wheels, ball races, jewel pivots etc.). The second significant issue is that the mass of the arm (not just the arm wand) is very different laterally to vertically and even a very tiny deviation from absolute level will apply significant side forces on the stylus (particularly an issue if level changes during play due to the shift of arm mass)
All of this has been said many times before, if it was true, the arm would sound terrible, it doesn't, so it would suggest things are not as they seem and the wrong logic is being applied. The design does use air pressure, or the sled would not lift. It doesn't centralise on a shaft, but rather than being seen as less sophisticated, read simpler and better, as much less air pressure is needed. For the horizontal mass, you are suggesting it is the combined mass of the wand and the sled. The wand is sitting on pin point bearings, which may effect things, after all you wouldn't add the support column mass to a uni-pivot arm. A record is an undulating and if not centred, wandering surface, there are massive forces applied due to this, cartridges deal with it. The tiny amounts of sled movement you are talking about, pale into insignificance, so sorry, I'm not convinced on that one.
For whatever reason, the design contradicts the logic being applied, it would be nice to understand why, but I'm not overly concerned about this and just enjoy what it does. The only down side for me, is I can't afford a cartridge good enough to do it justice, as it is a very good arm. :)
RothwellAudio
29-04-2017, 10:26
Records are cut using a linear tracker. Using a pivoting arm actually introduces more complications and issues to overcome.
Using linear tracking would appear to be the only sensible option for playback when you consider that linear moving cutters are used to make records in the first place. However, there's a major difference between cutting the record and playing it back - when cutting, the cutting heads are driven across the record surface whereas when playing back the stylus is carried across the record surface by the groove. When playing back the groove is pulling the cartridge towards the centre of the record but the cartridge is attached to an arm with a sliding mechanism at the other end. The force on the cartridge is applying a twisting force on the arm due to it being offset from the fixing point. If you think about it you'll see why the "arm" of a linear tracker is so short - it's to minimise the offset and hence the twisting force.
To me, that seems like a serious engineering problem to overcome. Obviously the simplicity of a pivoting arm is very attractive in comparison and the compromise in tracking accuracy has been seen historically as a price worth paying to avoid the engineering complexities of linear tracking. In a "cost no object" turntable it would make sense to try to go beyond a simple pivoting arm.
This Garrard Zero tonearm seems to me to be a great way to get the benefits of linear tracking in a simpler way, but it is still a complex piece of engineering to execute well.
http://www.quadibloc.com/science/images/tonearm.gif
There is no twisting force on a linear tracker as such, that's one of the benefits. The cantilever of a stylus gets pulled all over the place on a less than perfect record (majority) and the low resistance of the air bearing is a positive attribute in dealing with this.
A pivoting arm has overhang and offset and needs an anti skate pressure to resist the the arm being dragged across the grooves to the centre of the record.
The linear tracker naturally has zero overhang or offset, though it could be added, so no anti skate is normally needed and it just follows the groove. The levitating sled is so free to move that a puff of breath will send it flying along the arm and offers less resistance than even the best bearing race.
Any type of design getting sound out of the wrinkles in a vinyl surface is going to have huge issues to overcome, I just think the ones specific to linear type arms are over stated and don't effect play back nearly as much as people would have you believe. Folks have to decide for themselves which approach suits them, they all work, but not without some form of loss.
PS. Some designs of linear tracker were driven, one used a laser to follow the groove and motors to move the arm to keep up.
All of this has been said many times before, if it was true, the arm would sound terrible, it doesn't, so it would suggest things are not as they seem and the wrong logic is being applied. The design does use air pressure, or the sled would not lift. It doesn't centralise on a shaft, but rather than being seen as less sophisticated, read simpler and better, as much less air pressure is needed. For the horizontal mass, you are suggesting it is the combined mass of the wand and the sled. The wand is sitting on pin point bearings, which may effect things, after all you wouldn't add the support column mass to a uni-pivot arm. A record is an undulating and if not centred, wandering surface, there are massive forces applied due to this, cartridges deal with it. The tiny amounts of sled movement you are talking about, pale into insignificance, so sorry, I'm not convinced on that one.
For whatever reason, the design contradicts the logic being applied, it would be nice to understand why, but I'm not overly concerned about this and just enjoy what it does. The only down side for me, is I can't afford a cartridge good enough to do it justice, as it is a very good arm. :)
In short, I disagree with pretty much all your conclusions. The Ladegaard, on which the arm you refer to is closely based, can be tuned by altering the mass of the moving sled - this compresses the air film and the effects are clearly audible - particularly in the bass which is a traditional weak point in air bearing arms.
Air is pumped (lots of associated issues with that in itself) obviously - but the actual pressure is generated by gravity acting on the supported mass - that is also obvious.
Yes, when I write that the mass is very different in the two planes of movement I do mean the mass and not the effective mass of just the arm wand.
I don't know why you think the design is more elegant (it's certainly less technically capable) than fully constrained designs (unless it's because it can be made with basic tools).
Frankly I find your logic to be deeply flawed on this.
Nothing wrong with my logic, it depends on which design elements/issues you decide to highlight.
With a conventional air bearing having an enclosed air sleeve it may be constrained by the air pressure, which is not a high pressure, but the surface area is equally as important. The area the air is acting against, to resist rotational movement (twist), effecting variability of azimuth, is less than 1 square inch compared to approx 12 square inches on the Terminator. In this respect it is much more stable, but there will be other areas where it looses out, as non of them are perfect.
To hear you guys talk, the Terminator, or any other linear tracker, shouldn't be capable of anything other than a barely acceptable performance, mediocre at best. While it may not be the ultimate arm, that's something I just couldn't agree with, having used one.
RothwellAudio
29-04-2017, 14:07
There is no twisting force on a linear tracker as such, that's one of the benefits.
Yes there is but I probably failed to describe it adequately. I'll try again.
Consider a T-shaped structure with the top of the T being a tube and the upright portion of the T being a flat bar. The T-shape lies in a horizontal plane. The tube fits onto a round section bar so it can slide along it and the cartridge is fitted to the end of the flat bar. A force pushing directly on the tube will cause it to slide along the round bar with no twisting force. A force pushing on the end of the flat bar where the cartridge is located will have a component that twists the T-shaped structure with a tendency to lock it to the round bar rather than sliding along it. The longer the flat bar (ie the farther the cartridge is from the sliding tube) the greater the twisting force.
Some designs of linear tracker were driven.
Yes, that would mean the force on the sliding tube would have no twisting component, which is presumably why they were designed that way. But it's yet another level of engineering complexity.
BTW, you sound like you're feeling under attack. I don't think anyone is attacking you or the concept of linear tracking tonearms - just saying that there are pros and cons.
Rothwell - I see what your getting at, in describing the twist.
The amount of force required to move the cartridge sideways, to keep up with the spiralling groove is very small, albeit multiplied by the arm length.
The air bearing however is designed to keep the parts (Tube and rod) separated so they don't lock up, and can support the whole weight of the arm, many times the force applied by the cartridge, so it shouldn't be an issue.
The design used on my arm doesn't actually have a tube, its a piece of equal angle extrusion that runs on the top edge of a square profile track, that has holes in it, bit like a saddle, but it would offer similar resistance.
Coming under attack - feels a bit like that, not me personally, but the concept of a parallel tracker.
Some folks obviously feel its a Marmite situation, I don't mind that, the banter has been constructive, so it's not a problem for me.
I think people know where I stand on the subject and all seem to agree there are issues with any design.
Still, its supposed to be a thread about the merits of different arm lengths. :D
RothwellAudio
29-04-2017, 20:50
Still, its supposed to be a thread about the merits of different arm lengths. :D
Absolutely correct, so here are some very interesting papers:
http://www.audiomods.co.uk/regafacts.html#theory
they're near the bottom of the page under "arm geometry".
Pickup arm design techniques by TS Randhawa (Wireless World, March 1978) is a very good one.
Ammonite Audio
30-04-2017, 07:24
It's interesting to read the Stevenson pieces, but his assertion that 'a pickup arm should be constructed so that its inertia or effective mass at the stylus tip is as small as possible' would not hold water today! Impressive mathematics skills though.
Enjoyed the Wireless World article, essential reading for anyone swapping out arms/cartridges.
It's interesting to read the Stevenson pieces, but his assertion that 'a pickup arm should be constructed so that its inertia or effective mass at the stylus tip is as small as possible' would not hold water today! Impressive mathematics skills though.
I think it's a sensible assertion, provided the design doesn't sacrifice rigidity for low inertia. One can always increase the inertia (and hence effective mass), but is difficult to reduce it.
Stevenson does make some small angle approximations which are not necessarily valid; but in practice they are largely self-cancelling.
The first and original paper on tonearm geometry was written by Loefgren. Unfortunately, being written in German, Loefgren's work was not widly promulgated. Baerwaldt later independently derived the same equations and explicitly derived formulae for the arm overhang and offset angle, and for the two null points used to design an alignment protractor.
Powered by vBulletin® Version 4.2.3 Copyright © 2026 vBulletin Solutions, Inc. All rights reserved.