Hi Niffy. I would almost completely agree with you. To split carriage into two parts is inevitable. However, if put them on opposite sides of platter, we may achieve symmetrical load on both, as well as on bearings, that is good news. Absence of counterweight gives some advantage in keeping longer carriage light enough. Actually, I already do have a concept drawings of such arm. I'm sure it has some substantial advantages over most of known linear arms, including user friendliness and convenience to load records...
Walter
Walter
Air bearing tonearm questions.
Newbie here. After reading the majority of postings on the thread, I am truly impressed with the quality level of the discussion, the willingness to help others, and the valuable information being disseminated. Congratulations to all involved! I do have a few questions of my own and would love some feedback. Concerning a linear tracking air bearing tonearm:
1) Is it always better to decouple the counterweight rather than have it rigidly attached?
2) Is it always better to use a heavier counterweight closer to the pivot point or could there be an advantage to a lighter counterweight further out on the balance arm which would result in a lower overall mass of the moving assembly?
3) If the heavier counterweight set-up is the preferred way to go, is this due to the lower polar moment of inertia provided by the location being closer to the pivot point and the added cantilever stability provided by the increased mass?
4) Assuming the increase in mass is beneficial, is there a practical point at which mass becomes problematic on an air bearing tonearm?
5) When establishing level on an air bearing tonearm, is it best to get it to float without sideways movement when no appreciable downforce is applied, or bias it to compensate for the slight inward slope inherent in most LPs by leveling it while "playing" a blank sided LP?
6) If the balance arm can be lowered from horizontal, which would change the vertical relationship of the counterweight to the carriage, what are the advantages and disadvantages of having the counterweight located below the pivot point as opposed to parallel to it? How would you determine the ideal position?
7) What would be the ideal vertical and horizontal resonant frequencies to achieve on an air bearing tonearm? I use a clamp that flattens most records but does not correct for off center pressings.
Newbie here. After reading the majority of postings on the thread, I am truly impressed with the quality level of the discussion, the willingness to help others, and the valuable information being disseminated. Congratulations to all involved! I do have a few questions of my own and would love some feedback. Concerning a linear tracking air bearing tonearm:
1) Is it always better to decouple the counterweight rather than have it rigidly attached?
2) Is it always better to use a heavier counterweight closer to the pivot point or could there be an advantage to a lighter counterweight further out on the balance arm which would result in a lower overall mass of the moving assembly?
3) If the heavier counterweight set-up is the preferred way to go, is this due to the lower polar moment of inertia provided by the location being closer to the pivot point and the added cantilever stability provided by the increased mass?
4) Assuming the increase in mass is beneficial, is there a practical point at which mass becomes problematic on an air bearing tonearm?
5) When establishing level on an air bearing tonearm, is it best to get it to float without sideways movement when no appreciable downforce is applied, or bias it to compensate for the slight inward slope inherent in most LPs by leveling it while "playing" a blank sided LP?
6) If the balance arm can be lowered from horizontal, which would change the vertical relationship of the counterweight to the carriage, what are the advantages and disadvantages of having the counterweight located below the pivot point as opposed to parallel to it? How would you determine the ideal position?
7) What would be the ideal vertical and horizontal resonant frequencies to achieve on an air bearing tonearm? I use a clamp that flattens most records but does not correct for off center pressings.
Last edited:
Welcome new member!
I think this thread is more about mechanical linear arm. If you want to build an air bearing arm. I would suggest to post under my thread or restart a new thread. I will be happy to share my experience. If you want to read my thread, I would suggest to start from last page since I have been updating the arm for last pass two years already. A lot of thins had been changed.
My thread
DIY Air Bearing Linear Arm
Jim
Last edited:
Hi newbie,
Welcome to the world of linear tracking. I would recommend a visit to Jim's air bearing tonearm thread, he's our resident expert in all things air bearing.
I will attempt to answer your questions here as well.
1. It is not necessarily better to decouple the counterweight. If you are building an arm with a short armtube the weight used will tend to be much smaller than a conventional pivoted tonearms. The main problem that decoupling is aimed at curing is sound reflection from the heavy counterweight. With a small counterweight the reflections are not be an issue. Also decoupling involves putting a compliance between the armtube and weight. A compliance plus a mass equals a resonance. So I would recommend against decoupling.
2. There is an optimum combination of mass to Counterweight location for any arm. This is largely dependent upon cartridge compliance. You want the vertical effective mass of the arm to match your cartridge compliance to give a vertical cantilever resonance of 8-12hz. I personally aim for the lower end of this range. A heavy counterweight close to the pivot will lead to a lower effective mass. A light counterweight far from the pivot leads to a higher effective mass. About a year ago I posted a couple of extensive articles in this thread concerning effective mass, how to calculate it and it's effects.
3. The polar moment of inertia is the more scientific term for effective mass. Answer 2 and the mentioned posts should cover this.
4. Jim probably has more experience in this area than I. The lateral effective mass of a linear tracking tonearm is equal to the total moving mass. Keep this mass low enough so that the lateral cantilever resonance is well above the frequency of record eccentricity, 0.55hz. Around 4-5hz is ideal. Again this is dependent upon cartridge compliance.
5. I defer to Jim.
6. It is not the location of the counterweight that matters. It is the location of the centre of mass of the whole arm including the counterweight that matters. The centre of mass should be level with the pivot point. If it is above the pivot tracking force will decrease as the arm traverses a warp. If below tracking force will decrease. If you have to have the com above or below it is preferable to have it slightly below as this is the more stable configuration. As you have a good clamp this location becomes less critical.
7. I personally aim for about 9.5hz vertical and 4.5hz lateral
Niffy
Welcome to the world of linear tracking. I would recommend a visit to Jim's air bearing tonearm thread, he's our resident expert in all things air bearing.
I will attempt to answer your questions here as well.
1. It is not necessarily better to decouple the counterweight. If you are building an arm with a short armtube the weight used will tend to be much smaller than a conventional pivoted tonearms. The main problem that decoupling is aimed at curing is sound reflection from the heavy counterweight. With a small counterweight the reflections are not be an issue. Also decoupling involves putting a compliance between the armtube and weight. A compliance plus a mass equals a resonance. So I would recommend against decoupling.
2. There is an optimum combination of mass to Counterweight location for any arm. This is largely dependent upon cartridge compliance. You want the vertical effective mass of the arm to match your cartridge compliance to give a vertical cantilever resonance of 8-12hz. I personally aim for the lower end of this range. A heavy counterweight close to the pivot will lead to a lower effective mass. A light counterweight far from the pivot leads to a higher effective mass. About a year ago I posted a couple of extensive articles in this thread concerning effective mass, how to calculate it and it's effects.
3. The polar moment of inertia is the more scientific term for effective mass. Answer 2 and the mentioned posts should cover this.
4. Jim probably has more experience in this area than I. The lateral effective mass of a linear tracking tonearm is equal to the total moving mass. Keep this mass low enough so that the lateral cantilever resonance is well above the frequency of record eccentricity, 0.55hz. Around 4-5hz is ideal. Again this is dependent upon cartridge compliance.
5. I defer to Jim.
6. It is not the location of the counterweight that matters. It is the location of the centre of mass of the whole arm including the counterweight that matters. The centre of mass should be level with the pivot point. If it is above the pivot tracking force will decrease as the arm traverses a warp. If below tracking force will decrease. If you have to have the com above or below it is preferable to have it slightly below as this is the more stable configuration. As you have a good clamp this location becomes less critical.
7. I personally aim for about 9.5hz vertical and 4.5hz lateral
Niffy
BWJ
I will put my 2 cents worth since Niffy started here. All the questions you asked I have had on my arms, too. I think you are very well papered and thought out. I didn’t know anything about air bearing arm when I started to build. I wasted money and time in the process.
Niffy has excellent points about air bearing/linear arm. I agree with him on most of his views. For some of his views, I won’t say I disagree with him, but my approach may be slightly different.
First, I would like to know what kind of air bearing arm you want to build.
Jim
I will put my 2 cents worth since Niffy started here. All the questions you asked I have had on my arms, too. I think you are very well papered and thought out. I didn’t know anything about air bearing arm when I started to build. I wasted money and time in the process.
Niffy has excellent points about air bearing/linear arm. I agree with him on most of his views. For some of his views, I won’t say I disagree with him, but my approach may be slightly different.
First, I would like to know what kind of air bearing arm you want to build.
Jim
Last edited:
Very informative post niffy. Thanks.
Thanks again and regards.
Couple of weeks ago I posted same query here #1515. I would be obliged if you give links to those articles. By the way I am not building anything. just learning as I find mechanical stuff interesting.
Thanks again and regards.
Thanks Niffy. Seems I have read that posts. What I was thinking about is mass distribution. For example. Weight of counterweight should be as near to pivot as possible but we have thomas schtik tonearm with long counterweight. Another example is I read some place that in unipivots the stabilising weight should be just below the pivot point* but I also see unipivots tonearm designs with very very low strung weights.
(*but not too far away from it as it will exert inertia while tracking warped records. )
So I was looking for what is the ideal arrangement with respect to mass and its effects on inertia etc.
Regards
(*but not too far away from it as it will exert inertia while tracking warped records. )
So I was looking for what is the ideal arrangement with respect to mass and its effects on inertia etc.
Regards
...would also like to know in tonearms tight tolerance are preferred. Unipivots are best in that regards. But how does string hanging pivot tonearms fair comparatively ? If we think about longitudinal push pull at the stylus point by high groove modulations it must be affecting string-tonearm joint at the pivot point. Isn't it ?
niffy, one question concerning your reply: In #6, you state that if the center of mass is above the pivot point, tracking force will be reduced when a warp is encountered. You also state that if the center of mass is below the pivot point, tracking force will also be reduced when a warp is encountered. Is that correct?
Hi Hiten,
With a unipivot the centre of mass has to be below the pivot in order to give stability especially for azimuth. This does mean tracking force will slightly increase whilst navigating a warp. With unipivots a small stabilizing weight a long way below the pivot will increase effective mass and a heavy one close to the pivot will decrease effective mass. The notable exception is the Graham phantom which has the COM level with the pivot and uses an ingenious magnet arrangement to stabilize the arm.
The effective mass of an arm IS the polar moment of inertia as seen/referenced to the stylus. Normally, in engineering, the polar moment of inertia is referenced to the radius of gyration. In tonearm design it is much better to reference to the stylus but in reality either reference point could be used.
Niffy
Thanks Niffy,
I am reading some very very old articles about tonearms and read somewhere that all moving (rotating) mass around the pivot/s should have inertia and so effective mass. But I don't see on a typical tonearm counterweight is added to the tonearm mass + compliance calculation or matching.
Regards.
So should various designs this (low hung / just below the pivot stabilizing weight) be calculated while matching the compliance of the cartridge. One way to have lower effective mass would be to have a weight hung by a thin long pin below the pivot (For stability without increasing the mass).
I am reading some very very old articles about tonearms and read somewhere that all moving (rotating) mass around the pivot/s should have inertia and so effective mass. But I don't see on a typical tonearm counterweight is added to the tonearm mass + compliance calculation or matching.
Regards.
Wire drag solution
Hi everyone.
Just a suggestion to overcome the drag from the wires:
A sledge with one threaded hole through and one non threaded hole with a Teflon bushing is placed over the two glass tubes, higher than the arm.
Through the threaded hole , a threaded rod that can be turned by a small motor. Through the non threaded hole , a steel rod, so the sledge can follow the arm.
Two opto sensors determine where the sledge is relative to the arm and controls the motor (servo).
The sledge can now move the wires and because it is @ the same location as the arm there is no drag on the arm.
Of course this arrangement could very easily be elaborated to make the arm automatic by determine where the arm is and automatically place it in a position where the leading groove is , lowering the lift and later determine when the arm has reached the lead out groove, activating the lift and return to rest...
Hi everyone.
Just a suggestion to overcome the drag from the wires:
A sledge with one threaded hole through and one non threaded hole with a Teflon bushing is placed over the two glass tubes, higher than the arm.
Through the threaded hole , a threaded rod that can be turned by a small motor. Through the non threaded hole , a steel rod, so the sledge can follow the arm.
Two opto sensors determine where the sledge is relative to the arm and controls the motor (servo).
The sledge can now move the wires and because it is @ the same location as the arm there is no drag on the arm.
Of course this arrangement could very easily be elaborated to make the arm automatic by determine where the arm is and automatically place it in a position where the leading groove is , lowering the lift and later determine when the arm has reached the lead out groove, activating the lift and return to rest...
Sorry I missed this post.
When calculating effective mass everything that moves has to be taken into account and that includes the counterweight. The total effective mass of the arm does need to be matched to the cartridge. With a unipivot, whether you use small stabilizing weights a long way below the pivot or larger ones closer to the pivot is dependent upon the effective mass of the rest of the arm.
Niffy
Sources or Specs for key components?
Niffy,
I wonder if it would be possible for you to summarise in a single post, the sources for the key components of your arm - or at least the specifications of them, so those of us wishing to reproduce what you've made can source the same things.
In particular, I'm thinking of:
1. The carbide rings (what eBay vendor did you get them from)
2. The sapphire V and abide points
3. The Carbon fibre (as we've seen, not all carbon fibre is the same)
4. The Tungsten Carbide rods themselves.
Niffy,
I wonder if it would be possible for you to summarise in a single post, the sources for the key components of your arm - or at least the specifications of them, so those of us wishing to reproduce what you've made can source the same things.
In particular, I'm thinking of:
1. The carbide rings (what eBay vendor did you get them from)
2. The sapphire V and abide points
3. The Carbon fibre (as we've seen, not all carbon fibre is the same)
4. The Tungsten Carbide rods themselves.
Hi alister
Sorry for the delay in answering, I'm following a lot of threads and missed your post.
1. I can't remember the vendor that I purchased the rings from. It was on eBay. I think they were an American based vendor but the rings were shipped from Thailand. They were sold as American size 2 wedding rings and are tiny, OD 16.2mm, ID 13.2mm and 2mm wide. The rings were available with a rounder or more square profile, I can't remember the jewellery terms for the shapes. From my experiments I determined that the square profile sounds better. I believe this is due to better mechanical grounding. These were perfect for my arm as they fitted the carriage and rails exactly and being the smallest size available were also the lightest. They were also stupidly cheap, about £3 each including postage. A real lucky find.
2. The sapphire vees were purchased from Amazon from vendor small parts in the states. The vee has a metric radius of 0.25mm but were sold with imperial measurements. The tungsten carbide pivots were purchased from Truepoint in the UK and had a tip radius of about 0.13mm. I'm quoting from memory so exact dimensions might be a tiny bit different but definitely close. Truepoint also sells sapphire vees but they are more expensive than from Amazon. The last time I looked small parts weren't trading. Building an alignment jig to make sure the pivots are exactly central to the wheels is essential.
3. I purchased my carbon fibre from carbonology in the UK. I had my carbon fibre specially laid up with the surface woven lamina orientated at 45° relative to the inner unidirectional fibres. This makes a big difference. If you can find a dealer that can make your composite sheet using UHM (ultra high modulus) carbon fibre rather than the standard grade HS (high strength) then do so. We're after maximum rigidity not strength. Also if you can have it cured in an autoclave do so, it squeezed the fibres closer together and improves the properties. Don't worry if you can't get UHM autoclave carbon fibre, you can make a killer arm with standard grade.
4. I was very kindly given my tungsten carbide rods by diy member hottattoo. Truepoint sell these rods.
Niffy