I looked at the place Joe posted but they do not ship to Australia, and finding a supplier here for carbide blanks in low qty has been unfruitful. I can get silver steel rods locally which are ground to H6 and straight to 3um/m. I was seriously considering using these.
.
Silver steel is prone to fine pit rusting if not kept oiled, stainless might be worth considering if it can be sourced to a sufficient surface quality especially if near the sea - salt air is unforgiving. Silver steel is better than mild steel of course, but that's not saying much.
Most silver steel rod (its got several names, basically a tool grade steel) is sold unhardened to make it easy to work. Hardening isn't super difficult to do, but then you need to polish the surface again.
Most silver steel rod (its got several names, basically a tool grade steel) is sold unhardened to make it easy to work. Hardening isn't super difficult to do, but then you need to polish the surface again.
Hi Warrjon,
What diameter are the glass rods you are currently using? The 4mm glass rods I sourced many years ago were from a medical supplier somewhere in the States. They were slightly variable in diameter, varying by about 0.1mm between rods. As the minimum order was for 25 rods this didn't cause an issue. More importantly the diameter was consistent within a rod. The rods appeared to be very straight but I did not test as thoroughly as you.
I hope you find a supplier of quality rods soon.
Niffy
What diameter are the glass rods you are currently using? The 4mm glass rods I sourced many years ago were from a medical supplier somewhere in the States. They were slightly variable in diameter, varying by about 0.1mm between rods. As the minimum order was for 25 rods this didn't cause an issue. More importantly the diameter was consistent within a rod. The rods appeared to be very straight but I did not test as thoroughly as you.
I hope you find a supplier of quality rods soon.
Niffy
Hi friends, congratulations for the level of precision you work at; I'm very impressed, being used to go under some cents* only with lapping, which is certainly not the ideal procedure for making a long, straight axis.
Rolling (like blueing, and together with go-no-go) still remain an incredible way of measuring. Yet so simple, and sometimes brutally convincing.
By the way, how are the microns / meter measured?
carlo
*using the old "paper trick"
Straight glass tubes, leaning to a wall for many time become bent glass tubes. Still remembering those of the chemistry lab of my high school days.
Rolling (like blueing, and together with go-no-go) still remain an incredible way of measuring. Yet so simple, and sometimes brutally convincing.
By the way, how are the microns / meter measured?
carlo
*using the old "paper trick"
Straight glass tubes, leaning to a wall for many time become bent glass tubes. Still remembering those of the chemistry lab of my high school days.
Hi all,
After watching Warren's video of his arm on an eccentric record I thought I'd try videoing my arm. Of course Murphy's law kicked in and every record I pulled out had virtually no eccentricity. Eventually I found a copy of Tracy Chapman which appears to have an eccentricity of about 0.3mm resulting in a side to side movement of about 0.6mm. Not as extreme as Warren's example.
YouTube
It was quite different to hold my phone still whilst I filmed this as I don't have a conventional plinth to hold the camera stabily against. The video is quite short as I was holding my breath.
The stylus doesn't appear to move relative to the cartridge body by very much at all which is good news and closely matches what I would expect based on the measurements I made of the bearings. This cartridge is quite high compliance and doesn't have a stabilising brush. The carriage is also quite heavy at 55g. Even an air bearing is not going to improve on this by a noticeable amount.
It's also worth noting that there is very little vertical movement. This is down to my clamping system being very effective.
A good result all round.
Niffy
After watching Warren's video of his arm on an eccentric record I thought I'd try videoing my arm. Of course Murphy's law kicked in and every record I pulled out had virtually no eccentricity. Eventually I found a copy of Tracy Chapman which appears to have an eccentricity of about 0.3mm resulting in a side to side movement of about 0.6mm. Not as extreme as Warren's example.
YouTube
It was quite different to hold my phone still whilst I filmed this as I don't have a conventional plinth to hold the camera stabily against. The video is quite short as I was holding my breath.
The stylus doesn't appear to move relative to the cartridge body by very much at all which is good news and closely matches what I would expect based on the measurements I made of the bearings. This cartridge is quite high compliance and doesn't have a stabilising brush. The carriage is also quite heavy at 55g. Even an air bearing is not going to improve on this by a noticeable amount.
It's also worth noting that there is very little vertical movement. This is down to my clamping system being very effective.
A good result all round.
Niffy
Niffy,
The arm tracks very nice in the video. When I did my video, I used The Ultimate Analog Test LP and expended the center hole a little to make an eccentric record.
Hi Jim,
I think I might have to pick out a junker record and enlarge the center hole to see how the arm performs under torture test conditions. I'll compare any test results to how my theoretical model compares.
It's very difficult to clearly see how much the cantilever moves in my video as the resolution is insufficient. I would estimate that the movement is about 10% the width of the cantilever and that the cantilever is about 0.4mm across. This would give a stylus displacement of about 40um. The cantilever is about 5mm long so peek LTA error will be about 0.45°. My model estimates that the maximum LTA error for a 0.3mm eccentricity will be around 0.42°. The difference is well within that which would be expected for my rough estimations of displacements (and not knowing exactly what cartridge compliance is at 0.55hz). I'm pretty happy with the results.
Niffy
I think I might have to pick out a junker record and enlarge the center hole to see how the arm performs under torture test conditions. I'll compare any test results to how my theoretical model compares.
It's very difficult to clearly see how much the cantilever moves in my video as the resolution is insufficient. I would estimate that the movement is about 10% the width of the cantilever and that the cantilever is about 0.4mm across. This would give a stylus displacement of about 40um. The cantilever is about 5mm long so peek LTA error will be about 0.45°. My model estimates that the maximum LTA error for a 0.3mm eccentricity will be around 0.42°. The difference is well within that which would be expected for my rough estimations of displacements (and not knowing exactly what cartridge compliance is at 0.55hz). I'm pretty happy with the results.
Niffy
That's what I did, I found an old record from my childhood of stories and filed the hole.
Quality Friction?
The concept of the phrase “the quality of cantilever movement due to friction” tickled my brain. On the one hand it’s an oxymoron since any cantilever movement due to friction is undesirable. On the other hand, in the context of stresses on a stylus cantilever and suspension, the quality or nature of the friction is very important. warrjon’s before and after videos illustrate this well:
YouTube
YouTube
The predominant manifestation of friction that I see is STICTION. The inward deflection of the cantilever gets progressively worse with each record rotation. When it reaches the point where the cantilever stress finally overcomes bearing stiction, the carriage suddenly breaks free and the energy pent-up in the stressed cantilever suspension ‘slingshots’ the carriage forward to where it often overshoots the ‘neutral balance’ point of cantilever suspension. The process repeats as the carriage ‘crabs’ across the record. Of course it is undesirable to have any type of lateral friction, but the predominance of a high amount of stiction would characterize the cantilever movement to be ‘low quality’. A high compliance cartridge is a sensitive barometer of the amount of stiction.
Not to bash diyer’s, here is what looks like a well-known commercial linear equipped with a low compliance cartridge and a Nasotec Swing Headshell:
YouTube
Notice that here we see the same deflection effect as in warrjon’s videos except that the Nasotec springs in the pivoting headshell are being deflected instead of the cantilever. I have seen numerous comments on the internet (if it’s on the internet it must be true, right?) that a bearing friction problem can be mitigated by using low compliance cartridges. In this case, the cantilever looks good and we assume it is good because we don’t see much cantilever deflection, but this is a deceptive picture. We see the headshell springs being deflected and that stress is passed on to the cantilever, too. The cantilever is still being stressed, it’s just not visually apparent.
Having said that, it seems to me that you guys are diy’ing better linear arms than commercial products costing $$$$$. Well done.
Ray K
The concept of the phrase “the quality of cantilever movement due to friction” tickled my brain. On the one hand it’s an oxymoron since any cantilever movement due to friction is undesirable. On the other hand, in the context of stresses on a stylus cantilever and suspension, the quality or nature of the friction is very important. warrjon’s before and after videos illustrate this well:
YouTube
YouTube
The predominant manifestation of friction that I see is STICTION. The inward deflection of the cantilever gets progressively worse with each record rotation. When it reaches the point where the cantilever stress finally overcomes bearing stiction, the carriage suddenly breaks free and the energy pent-up in the stressed cantilever suspension ‘slingshots’ the carriage forward to where it often overshoots the ‘neutral balance’ point of cantilever suspension. The process repeats as the carriage ‘crabs’ across the record. Of course it is undesirable to have any type of lateral friction, but the predominance of a high amount of stiction would characterize the cantilever movement to be ‘low quality’. A high compliance cartridge is a sensitive barometer of the amount of stiction.
Not to bash diyer’s, here is what looks like a well-known commercial linear equipped with a low compliance cartridge and a Nasotec Swing Headshell:
YouTube
Notice that here we see the same deflection effect as in warrjon’s videos except that the Nasotec springs in the pivoting headshell are being deflected instead of the cantilever. I have seen numerous comments on the internet (if it’s on the internet it must be true, right?) that a bearing friction problem can be mitigated by using low compliance cartridges. In this case, the cantilever looks good and we assume it is good because we don’t see much cantilever deflection, but this is a deceptive picture. We see the headshell springs being deflected and that stress is passed on to the cantilever, too. The cantilever is still being stressed, it’s just not visually apparent.
Having said that, it seems to me that you guys are diy’ing better linear arms than commercial products costing $$$$$. Well done.
Ray K
I'm really happy to finally see some videos: eyes are much less forgiving than ears, and I believe we owe to ourselves and our "colleagues" the tangible proof of our experiments - the good and bad ones.
Above all, unlike sellers, we diyer don't have anything to loose, and always something to learn.
Even happier for Ray's intervention about the "quality of cantilever movement" (it shouldn't exist...but it always exist, with it's reprehensible qualities), and on the effects of low compliance, taken as a remedy for inadequate TAs (#3261)
Over the years I have started to think that even more than for the basic resonance, the effective mass counts simply as it is: an inertia. The -stylus+elastomer+lever lenght+effective mass- (+electrical loading?) system behaves like a spring composite pendulum, capable of chaotic movements. Eccentricity is what generates the movement, and it's effects do not end in a single cycle but tend to influence themselves differently with various eff mass and friction, as I have attempted to describe.
Now we should take another step: define the condition of the experiment: for Lil casey I have used a junk disc with the hole brought to 8.5 mm (+-1,5 mm offset) and a thickness of 3 mm under the disc for the warp: excessive conditions, to avoid completely for listening, but excellent to highlight the TAs behavior.
And yes - the camera has to stand completely still: without a tripod a compact camera or a cell phone can be secured also with 2 pieces of duct tape.
carlo
Above all, unlike sellers, we diyer don't have anything to loose, and always something to learn.
Even happier for Ray's intervention about the "quality of cantilever movement" (it shouldn't exist...but it always exist, with it's reprehensible qualities), and on the effects of low compliance, taken as a remedy for inadequate TAs (#3261)
Over the years I have started to think that even more than for the basic resonance, the effective mass counts simply as it is: an inertia. The -stylus+elastomer+lever lenght+effective mass- (+electrical loading?) system behaves like a spring composite pendulum, capable of chaotic movements. Eccentricity is what generates the movement, and it's effects do not end in a single cycle but tend to influence themselves differently with various eff mass and friction, as I have attempted to describe.
Now we should take another step: define the condition of the experiment: for Lil casey I have used a junk disc with the hole brought to 8.5 mm (+-1,5 mm offset) and a thickness of 3 mm under the disc for the warp: excessive conditions, to avoid completely for listening, but excellent to highlight the TAs behavior.
And yes - the camera has to stand completely still: without a tripod a compact camera or a cell phone can be secured also with 2 pieces of duct tape.
carlo
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....even more complicated than these
YouTube
myPhysicsLab Double Pendulum
Double Pendulum -- from Eric Weisstein's World of Physics
YouTube
myPhysicsLab Double Pendulum
Double Pendulum -- from Eric Weisstein's World of Physics
The nasotec head shell definitely seems to reduce both of the problems with friction deflecting the cantilever. The cantilever in rays video appears to remain aligned with the cartridge body so generator should remain aligned. The point about which the cantilever is pivoted is moved backwards to the headshell pivot. Any rotations about this pivot will be lower in angle. However the arm seems to make very large and infrequent jumps so the angle is likely to be building up quite a bit before the jump. How this system is going to effect effective mass, overall rigidity and coupling is another important part of the way the system performs. I'm not convinced.
It's difficult to determine much from the video of the cantus except that the deck has truly awful runout of the platter.
Niffy
It's difficult to determine much from the video of the cantus except that the deck has truly awful runout of the platter.
Niffy
Torture test and cat hair.
Hi all,
Here is a video of a cat hair going round and round on a record. The eagle eyed of you might also spot my cartridge wagging back and forth dramatically. I filed out the hole of an old record (that felt so wrong, almost sacrilegious) to give an eccentricity of 1.6mm so the arm will be moving back and forth by 3.2mm (1/8"). A proper torture test.
YouTube
For this level of eccentricity I would calculate that the cantilever would be deflected by 56um for my arm and cartridge. This will result in a maximum LTA error of about 0.65°, the average error will be about 0.42°. 56um would be around a 7th the width of the cantilever. This is pretty much what we see in the video. As with the previous video the exact amount of cantilever defection is really difficult to accurately determine, on a quick glance there doesn't seem to be any relative movement at all.
Of course you would never have eccentricity anywhere near as extreme as this test. The average LTA error for a more average record will be more like 0.25-0.3°, the largest contribution will still be bearing friction.
As with the previous video I'm really pleased with the lack of vertical movement. Not only does this show that warps are being effectively flattened but also that platter runout is minimal. My decks main bearing is sleeveless, basically a unipivot, and an out of balance record could cause platter runout problems. I have the motor and 2 idlers positioned around the bearing with 3 separate belts. This seems to have eliminated any runout issues.
Again I'm really pleased with the results of this test.
Niffy
Hi all,
Here is a video of a cat hair going round and round on a record. The eagle eyed of you might also spot my cartridge wagging back and forth dramatically. I filed out the hole of an old record (that felt so wrong, almost sacrilegious) to give an eccentricity of 1.6mm so the arm will be moving back and forth by 3.2mm (1/8"). A proper torture test.
YouTube
For this level of eccentricity I would calculate that the cantilever would be deflected by 56um for my arm and cartridge. This will result in a maximum LTA error of about 0.65°, the average error will be about 0.42°. 56um would be around a 7th the width of the cantilever. This is pretty much what we see in the video. As with the previous video the exact amount of cantilever defection is really difficult to accurately determine, on a quick glance there doesn't seem to be any relative movement at all.
Of course you would never have eccentricity anywhere near as extreme as this test. The average LTA error for a more average record will be more like 0.25-0.3°, the largest contribution will still be bearing friction.
As with the previous video I'm really pleased with the lack of vertical movement. Not only does this show that warps are being effectively flattened but also that platter runout is minimal. My decks main bearing is sleeveless, basically a unipivot, and an out of balance record could cause platter runout problems. I have the motor and 2 idlers positioned around the bearing with 3 separate belts. This seems to have eliminated any runout issues.
Again I'm really pleased with the results of this test.
Niffy
Again I'm really pleased with the results of this test.
me too Niffy, congratulations: really a great result, very difficult to achieve/equal.
This confirm with evidence your hypothesis (and calcs) that friction is the only key to (your carriage was under 1mN, if i remember well) and not also the inertia, as I was wrongly supposing.
So the delay of the carriage movement, that can be often observed, must be charged solely to stiction vs friction ratio, as Ray wisely noted.
Now it remains to be understood why high mass pivoted ones also show similar behaviors, (cantilever moving relatively to heavy headshell) even if they usually have low friction bearings, and long favorable leverage.
carlo
me too Niffy, congratulations: really a great result, very difficult to achieve/equal.
This confirm with evidence your hypothesis (and calcs) that friction is the only key to (your carriage was under 1mN, if i remember well) and not also the inertia, as I was wrongly supposing.
So the delay of the carriage movement, that can be often observed, must be charged solely to stiction vs friction ratio, as Ray wisely noted.
Now it remains to be understood why high mass pivoted ones also show similar behaviors, (cantilever moving relatively to heavy headshell) even if they usually have low friction bearings, and long favorable leverage.
carlo
One of the most pervasive myths about linear tracking arms is that the high lateral effective mass will result in the cantilever being displaced on eccentric records to a degree that causes LTA errors to be greater than those due to the geometry of a conventional pivoted arm, the tail wagging the dog.
In reality the negative effects of the lateral inertia of the arm are minimal. The lateral mass of my arm is 4 times as great as the vertical so according to the myth should cause all sorts of tracking problems. Clearly from the videos it doesn't. Even with the extreme torture record the LTA error would have an average of 0.13° due to just the inertia. The real world record from the first video would have resulted in an average error of 0.036° due to inertia alone. The LTA error due to the groove angle on this record due to the eccentricity would have been about 0.15°. It is also worth noting that all arms have effective mass so will have an inertial effect to some degree.
Having a higher effective mass in the lateral plane at audio frequencies is actually beneficial as it controls the motion of the cartridge better. This is most noticeable in the bass and could explain why Warren noticed an improvement in this area compared to his reference arm.
Having a higher lateral effective mass is not really detrimental and actually has a positive effect on sound quality.
Myth busted.
Niffy
In reality the negative effects of the lateral inertia of the arm are minimal. The lateral mass of my arm is 4 times as great as the vertical so according to the myth should cause all sorts of tracking problems. Clearly from the videos it doesn't. Even with the extreme torture record the LTA error would have an average of 0.13° due to just the inertia. The real world record from the first video would have resulted in an average error of 0.036° due to inertia alone. The LTA error due to the groove angle on this record due to the eccentricity would have been about 0.15°. It is also worth noting that all arms have effective mass so will have an inertial effect to some degree.
Having a higher effective mass in the lateral plane at audio frequencies is actually beneficial as it controls the motion of the cartridge better. This is most noticeable in the bass and could explain why Warren noticed an improvement in this area compared to his reference arm.
Having a higher lateral effective mass is not really detrimental and actually has a positive effect on sound quality.
Myth busted.
Niffy
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Here is a video I did in Aug last year. I expended the center hold so the eccentricity is about 2-3 mm. The LP is The Ultimate Test LP. This test LP is an eccentric LP so actual eccentricity can be greater than 2 mm. The track was 1K Hz. I posted this video in my air bearing thread before.
YouTube
The myth is that vertical effective mass should be equal to lateral effective mass. So, your answer is slightly different.
For a linear arm, its effective mass is the same as its total mass, so I will use the word total mass only. I can’t agree more that heavy lateral mass helps the performance of a linear arm. But it is under some conditions.
Let’s assume there is a linear arm with no lateral friction at all.
There are two forces to drive a cartridge. 1st one is the force generated by the spiral groove. It drives a cartridge to move inwards. I call that force, F1. 2nd force is the force generated by the micro waveform which embedded on the wall of the groove. This is music information. The waveform causes vibration of the cantilever of a cartridge. I call that force, F2.
I also define the force to overcome the gravity of the total mass of arm as F3. There is another force which is to cause the displacement of cantilever. This force can be expressed as the compliance of a cartridge.
In summary,
F1=the force generated by the spiral groove.
F2=the force generated by micro waveform.
F3=the force to move total mass.
F4=the force to displace cantilever.
An optimal mass of a linear arm, I.e. F3, should be
F4>F1> or = F3>F2
F3 is a function of total mass and friction. Since friction is zero here. For example, air bearing arm.
F3=f(total mass)
For mechanical linear arm,
F3=f(total mass, friction)
My conclusion is that total mass F3 should not stronger than F4, but stronger or the same as F1. Within that range, the heavier the total mass, the better the performance. F4 is the limit of all forces. In other words, the compliance of a cartridge is the maximum force you may apply to that cartridge. Any force that is stronger than F4 will degrade the performance. This also explains why a low compliance cartridge is preferred for linear arms.
YouTube
The myth is that vertical effective mass should be equal to lateral effective mass. So, your answer is slightly different.
For a linear arm, its effective mass is the same as its total mass, so I will use the word total mass only. I can’t agree more that heavy lateral mass helps the performance of a linear arm. But it is under some conditions.
Let’s assume there is a linear arm with no lateral friction at all.
There are two forces to drive a cartridge. 1st one is the force generated by the spiral groove. It drives a cartridge to move inwards. I call that force, F1. 2nd force is the force generated by the micro waveform which embedded on the wall of the groove. This is music information. The waveform causes vibration of the cantilever of a cartridge. I call that force, F2.
I also define the force to overcome the gravity of the total mass of arm as F3. There is another force which is to cause the displacement of cantilever. This force can be expressed as the compliance of a cartridge.
In summary,
F1=the force generated by the spiral groove.
F2=the force generated by micro waveform.
F3=the force to move total mass.
F4=the force to displace cantilever.
An optimal mass of a linear arm, I.e. F3, should be
F4>F1> or = F3>F2
F3 is a function of total mass and friction. Since friction is zero here. For example, air bearing arm.
F3=f(total mass)
For mechanical linear arm,
F3=f(total mass, friction)
My conclusion is that total mass F3 should not stronger than F4, but stronger or the same as F1. Within that range, the heavier the total mass, the better the performance. F4 is the limit of all forces. In other words, the compliance of a cartridge is the maximum force you may apply to that cartridge. Any force that is stronger than F4 will degrade the performance. This also explains why a low compliance cartridge is preferred for linear arms.
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Hi Jim,
All of the forces you discribe are actually the same force, that between the groove wall and the stylus. What diferentiates the way this force manifests is frequency. The combination of the mass of the arm and the cartridge compliance will have a resonant frequency. The behaviour of the system can be split into three parts, below resonance, above resonance and at resonance.
Again I will start by assuming no friction and will only consider lateral movement.
Below resonance.
If the record is concentric then the amount of force required to move the arm will be very small as there is no acceleration.
If the record is eccentric then a force will be generated to accelerate and decelerate the arm as it moves from side to side. The magnitude of the force will be dependent upon the speed of rotation of the record, the mass of the arm and the severity of the eccentricity.
In both of these cases the force will be in phase with the motion of the arm. The force will cause a deflection of the cantilever. The magnitude of the deflection will depend on the compliance of the cartridge as well as the speed of rotation of the record, the mass of the arm and the severity of the eccentricity.
Above resonance.
This is where the audio signal is recorded. As the stylus is moved back and forth by the modulation of the groove wall the cartridge body/arm will move out of phase with the groove. The amount the arm moves relative to the stylus will decrease with frequency reducing by 12dB/octave. Reducing by a quarter every time the frequency doubles. At 20hz the movement of the arm can be only 10dB below that of the stylus, over a quarter, for an arm tuned to 10hz. By the time you get to 120hz the movement of the arm should be down to -60dB, 1000th the movement of the stylus.
At resonance.
At resonance the arm moves at - 90° phase relative to the movement of stylus and can easily be moving by 8-12dB more, up to 4 time the movement of the stylus.
There are two other forces that effect the performance of the arm.
Bearing friction which will have static (stiction) and dynamic elements. As an arm moves back and forth due to eccentricity the arm will start off stationary and won't move until its static friction is overcome then will begin to move. At this point the level of friction will decrease to the dynamic friction level until the arm stops. These friction will result in a side force acting on the stylus that will cause the cantilever to be deflected. The greater the friction and the higher the compliance the greater the deflection.
The final force is that supplied by damping. This will be the natural damping of the cartridges suspension and any additional external damping such as a silicone fluid trough. This damping resists the motion of the arm ideally slowing the motion of the arm.
All of the forces will displace the cantilever. Ideally you want the displacement to be as small as possible below resonance and to be equal to the groove modulation above resonance.
Niffy
All of the forces you discribe are actually the same force, that between the groove wall and the stylus. What diferentiates the way this force manifests is frequency. The combination of the mass of the arm and the cartridge compliance will have a resonant frequency. The behaviour of the system can be split into three parts, below resonance, above resonance and at resonance.
Again I will start by assuming no friction and will only consider lateral movement.
Below resonance.
If the record is concentric then the amount of force required to move the arm will be very small as there is no acceleration.
If the record is eccentric then a force will be generated to accelerate and decelerate the arm as it moves from side to side. The magnitude of the force will be dependent upon the speed of rotation of the record, the mass of the arm and the severity of the eccentricity.
In both of these cases the force will be in phase with the motion of the arm. The force will cause a deflection of the cantilever. The magnitude of the deflection will depend on the compliance of the cartridge as well as the speed of rotation of the record, the mass of the arm and the severity of the eccentricity.
Above resonance.
This is where the audio signal is recorded. As the stylus is moved back and forth by the modulation of the groove wall the cartridge body/arm will move out of phase with the groove. The amount the arm moves relative to the stylus will decrease with frequency reducing by 12dB/octave. Reducing by a quarter every time the frequency doubles. At 20hz the movement of the arm can be only 10dB below that of the stylus, over a quarter, for an arm tuned to 10hz. By the time you get to 120hz the movement of the arm should be down to -60dB, 1000th the movement of the stylus.
At resonance.
At resonance the arm moves at - 90° phase relative to the movement of stylus and can easily be moving by 8-12dB more, up to 4 time the movement of the stylus.
There are two other forces that effect the performance of the arm.
Bearing friction which will have static (stiction) and dynamic elements. As an arm moves back and forth due to eccentricity the arm will start off stationary and won't move until its static friction is overcome then will begin to move. At this point the level of friction will decrease to the dynamic friction level until the arm stops. These friction will result in a side force acting on the stylus that will cause the cantilever to be deflected. The greater the friction and the higher the compliance the greater the deflection.
The final force is that supplied by damping. This will be the natural damping of the cartridges suspension and any additional external damping such as a silicone fluid trough. This damping resists the motion of the arm ideally slowing the motion of the arm.
All of the forces will displace the cantilever. Ideally you want the displacement to be as small as possible below resonance and to be equal to the groove modulation above resonance.
Niffy