If you use electrical metaphors - how can something be high impedance and ground at the same time???
Levitation provides mass as mechanical ground - this is BS.
The effective mass will be lower because of the missing CW. And the levitation does not change the effective mass.
I understand, but ^this^ is not what I'm proposing, or even think possible.
Only that you can have a counterweight that has no effect on the inertial mass of the complete arm. The wand of the arm still completes the, I=mr^2 formula.
You then have the freedom to "spend" some mass from the CW (now missing from the effective mass) on improving the wand or making it easier to get to your target effective mass.
I think this is only applicable to the horizontal effective mass.
You are going to have to help me out here, please.
What I'm reading is that we should all be experiencing high effective mass arms as better than low effective mass? At what compliance?
I cannot find two people in a crowded room to agree on what is the best.
This would be a lot easier if there was an empirical "best" relation between effective mass and cart compliance.
The inertial mass of the arm integrates the energy from the stylus, acting as a mechanical filter. Therefore, the ideal arm would have infinite mass, whilst also being able to follow the groove, regardless of stylus compliance.
In a conventional counter balance, the momentum of the counter weight is almost equal to the momentum of the wand. Since the momentum is summed, the arm keeps moving when disturbed. Magnets, springs etc, change the momentum balance.
In a conventional counter balance, the momentum of the counter weight is almost equal to the momentum of the wand. Since the momentum is summed, the arm keeps moving when disturbed. Magnets, springs etc, change the momentum balance.
I did not convey my message very well.
I will agree that a tonearm has 2DoF while NOT on the LP. Which is not the condition we are discussing.
As soon as the stylus hits the LP the system has 4 DoF at the stylus tip.
In simple terms this becomes a dual pendulum. The arm wand and cartridge cantilever. The arm wand has 2 DoF and the stylus CL has 2 DoF.
simple explanation.
If you have a tonearm with 2g VTF and add 100g of mass directly over the pivot because gravity is pulling down on it through the pivot there will be no addition VTF.
To calcluate EM you need to calculate the moment of inertia of the total system
If you calculate I for a 200g CW 20mm from the pivot is would be about 800g cm^2.
Then calculate I for the cartridge bolts 1.5g at 230mm from the pivot would be about 794g cm^2.
Both add about 1.4g to the total EM of the arm.
Switching between different topics and same people arguing back and forth i lost count of who said what...
I just realized that it wasn't the topic author who described the magnetic loading as a source for lower effective mass...Magnetic or real counterweight, they exhibit same effective mass with the addition of a magnet repelling square law enforcing better damping, maybe better than a swinging counterweight , although not sure about that.If magnets are very powerful then it is posible that the damping would be very effective and the square law wouldn't present same effects as a linear one even with small vertical oscillations.
On the other hand a feedback system as Sony biotracer should provide better theoretical damping than a simple magnet or electromagnet with feedback and the fact that Sony biotracer is using a real counterweight too is because it's prefferable to load an electrical system and provide a low pass filter to filter away high freqeancy electrical oscillations.I looked at the first three videos and i saw in one of them that it happened once that the distance(or angle) between stylus and cartridge wasn't the same all the time , it looked like there was a latch on a different height level and that is why i think sony biotracer is still using a real counterweight to help low pass higher ferquency electrical ocillations and not providing them a way to integrate in the final signal .
I used to fix and callibrate Mettler Toledo and Kern analytical weighing scales 13 years ago and i remember that all of them used both electrical and mechanical loading to get faster and cleaner results and also counteract the difference in gravitational force in different places on Earth, whereas all the mechanical loading cell constants were stored in a memory and factored in the actual electrical measurements to give the final result .Basically you could convert any such weighing scale into a biotracer system by removing some of the 4...5 digits you could get under 200grams loading at that time.I saw that they extended their max weight at that precision to 320 grams recently....Of course you wouldn't need such precision in a turntable and it would also be imposible to get it with a stylus dragging on a moving groove too...but i suppose that the system is using the same principles as biotracer's.
I just realized that it wasn't the topic author who described the magnetic loading as a source for lower effective mass...Magnetic or real counterweight, they exhibit same effective mass with the addition of a magnet repelling square law enforcing better damping, maybe better than a swinging counterweight , although not sure about that.If magnets are very powerful then it is posible that the damping would be very effective and the square law wouldn't present same effects as a linear one even with small vertical oscillations.
On the other hand a feedback system as Sony biotracer should provide better theoretical damping than a simple magnet or electromagnet with feedback and the fact that Sony biotracer is using a real counterweight too is because it's prefferable to load an electrical system and provide a low pass filter to filter away high freqeancy electrical oscillations.I looked at the first three videos and i saw in one of them that it happened once that the distance(or angle) between stylus and cartridge wasn't the same all the time , it looked like there was a latch on a different height level and that is why i think sony biotracer is still using a real counterweight to help low pass higher ferquency electrical ocillations and not providing them a way to integrate in the final signal .
I used to fix and callibrate Mettler Toledo and Kern analytical weighing scales 13 years ago and i remember that all of them used both electrical and mechanical loading to get faster and cleaner results and also counteract the difference in gravitational force in different places on Earth, whereas all the mechanical loading cell constants were stored in a memory and factored in the actual electrical measurements to give the final result .Basically you could convert any such weighing scale into a biotracer system by removing some of the 4...5 digits you could get under 200grams loading at that time.I saw that they extended their max weight at that precision to 320 grams recently....Of course you wouldn't need such precision in a turntable and it would also be imposible to get it with a stylus dragging on a moving groove too...but i suppose that the system is using the same principles as biotracer's.
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Sorry for imprecise / confusing language. I'll try to explain it better.
Acoustic / mechanical Impedance & grounds.
Here's the mathematics:-
Acoustic impedance - Wikipedia
Impedance matching - Wikipedia
This one explains it in English words:-
sound - Impedance | Britannica
"Acoustic impedance is a measure of the ease with which a sound wave propagates through a particular medium."
Sound waves would be blocked from propagating through a high acoustic impedance medium. Whereas sound waves can propagate freely through a low acoustic impedance medium.
Lets picture in our minds an electro-mechanical transducer designed to measure spacial displacements, such as a cartridge cantilever. It has two ends. Since its the difference in displacement between each end that we're trying to measure, one end must be fixed in space. The other end must be free to follow the vibrations.
It thus seems appropriate to label the end rigidly fixed in space as a “ground” and the other end as “signal”.
If we accept the above definition of acoustic impedance” and our transducer labels, then it follows our “ground” must have a “high acoustic impedance”.
Standard CW arms have “effective mass” in the range of 10g or 20g. The actual mass is ten or twenty times more, c300g. This is because they are flywheels, optimised to store and release potential energy i.e. acoustic vibrations. My essay covers all this.
Voyd Reference Io Ltd. no counterweight SME V - Google Drive
Lets picture in our minds a pendulum held at 90 degrees to gravity (i.e. an arm wand). Lets put a weighing scales under the opposite end to its pivot (where the cartridge is). Lets suppose the scales read 100g. Lets now put a pair of magnets with like poles facing, between the scales and pendulum end. What will the scales now read? Ignoring magnet mass it'll still be 100g.
Such a pendulum arrangement is very bad at storing potential acoustic vibrational energy compared to a flywheel. Its "effective mass" is its actual mass of 100g according to the weighing scales.
(Pseudo) Magnetic Levitation: Lets take the magnet off the scales and mount it on the left/ right gimbal. The 100g is now pressing on the entire weight of the turntable (ignoring whatever lever ratios are needed to mount the magnets in this way).
A Valley of Stability: Acoustic vibrations (i.e. potential energy) induced in the pendulum's cartridge end, are met with a non linear reaction force due to magnetic force square law as they oscillate between the pendulum's rest position.
Groove forces in the up direction (i.e. axis perpendicular to the magnet like poles) are met with the magnetic repelling force dropping off exponentially, being replaced by the gravitational force quickly ramping up to all 100g of the mass, depending on groove vibration amplitudes and frequencies.
While in the down direction the magnets take over entirely connecting our 100g pendulum to the entire mass of the turntable.
Thus a non linear mass oscillation system in the axis perpendicular to the magnet like poles (i.e. up / down) is created. A Valley of Stability is thus created at the cartridge's reference pivot point for groove vibrations to react against.
Hope this explains a bit better what I think is going on - please do offer further insights and corrections, meanwhile I'm genuinely not trying to offer BS, thanks.
(As such, I think my essay / paper would have been more accurate to describe a gimbal tone arm's two degrees of freedom as “Tilts forward and backward (pitching)” and “Swivels left and right (yawing)” (instead of the colloquial labels I did use: “up and down & side to side” which are both translational degrees, but which a gimbal bearing does not possess!)
Re: "effective mass". Do pendulums and flywheels have different mechanical mathematics formula?
Re: videos. Thanks for looking at my videos. Yes you saw correct. The cartridge cantilever deflection (VTA if you like) can be set by adjusting coil current through (pseudo) magnetic levitation system on tone arm. The correct deflection angle is a proxy for a counterweighted arm's nominal 2g "tracking force".
Re: analytical weighing scales - Wow! Super Cool
The tonearm MUST have a certain effective mass to avoid resonances at the warp or bass frequencies.
The CW counts into the effective mass, so when you remove the CW, you MUST add mass elsewhere. It can be smaller than the mass of the CW but then it has to be nearer to the cartridge.
The mass "seen" by the stylus will be the same as with the CW, the energy storing effect you called "flywheel" remains the same too.
Remains the "damping" effect of the magnetical counterforce (by no way "levitation"). It is not real damping because damping relates to the velocity and not the distance.
The magnet has the effect that when the stylus has to accelerate the effective mass (warp) the counterforce decreases too, increasing the deflection of the stylus.
I would not call this effect advantegous.
The CW counts into the effective mass, so when you remove the CW, you MUST add mass elsewhere. It can be smaller than the mass of the CW but then it has to be nearer to the cartridge.
The mass "seen" by the stylus will be the same as with the CW, the energy storing effect you called "flywheel" remains the same too.
Remains the "damping" effect of the magnetical counterforce (by no way "levitation"). It is not real damping because damping relates to the velocity and not the distance.
The magnet has the effect that when the stylus has to accelerate the effective mass (warp) the counterforce decreases too, increasing the deflection of the stylus.
I would not call this effect advantegous.
Thanks spladski, I think you are describing what I've been trying to say.
Would you describe in more detail "integrates the energy"? And how is this related to the "acoustic impedance" the energy from the stylus acts against?
And how magnets, springs etc, change the momentum balance?
Thanks very much!
The mass of tonearm wand with headshell and cartridge is far from 100 g. When the COG is about the middle of the wand, the VTF does not exceed one half of the weight of the wand, even if the magnetic force would be zero.
So the claim that "the gravitational force quickly ramping up to all 100g of the mass," is nonsensical.
On the other side, the change in VTF does not alter the effective mass of the arm, and that is what counts. The effective mass seen by the stylus remains the same.
Please explain why “when you remove the CW, you MUST add mass elsewhere”? Surely this only applies when mass is arranged as flywheel to keep the arm/cartridge suspension resonance frequency the same? I don't understand how this is relevant to max potential energy pendulum (see below)?
Are you saying that the potential energy of a stationary mass with reference to a (2 degrees of freedom) pivot point at the centre of the mass (a flywheel), would have the same potential energy if that mass were instead configured as a beam (at the same radius and 2 degrees of freedom pivot point as the flywheel) with its end held at 90 degrees to gravity i.e. at its maximum potential energy?
But induced groove vibrations acting against the rest position of the tonearm / cartridge body mass are velocity, which in turn act against the (pseudo) levitation magnets, which is “real damping” used in many other applications. For example in this magnetic (Faraday harvester) levitation device “cubic nonlinearity comes from the magnetic restoring forces between the magnets” i.e. time domain damping.
Sensors | Free Full-Text | Theoretical and Experimental Investigations of a Pseudo-Magnetic Levitation System for Energy Harvesting | HTML
Lots more here too
Electromagnetic Levitation
(pseudo) magnetic levitation at DuckDuckGo
Please explain this in more detail, as I don't understand what you mean here?
Thanks!
Sorry, I thought I'd made it clear the 100 grams 'arm wand' number is nominal. The principal remains. Let my try to explain better.
The 'Mag-Lev' tone arm wand is a lever with a pivot at one end. A tracking force gauge (VTF) under the cartridge (with the arm's repelling magnets adjusted to be too far apart to have any effect at all) will measure 'AW' grams of mass (i.e. just as you wrote: "COG is about the middle of the wand, the VTF does not exceed one half of the weight of the wand").
The gravitational force acting on 'AW' grams of arm wand mass is of course constant at whatever distance between the repelling magnets.
To play records the magnets are adjusted to apply the correct cantilever deflection / tracking force 'TF' grams.
'TF' grams is between 10 and 100 times smaller than 'AW' grams.
Note: In 'Mag-Lev' geometry the magnets bypass the "pitching" (up and down) pivot, with 'AW' (minus 'TF' mass) coupled directly to the "yawing" (side to side) pivot & onto the turntable.
At rest in a record groove, nearly all the 'AW' grams mass force is transferred via the magnets but only to the arm's "yawing" (side to side) pivot & onto the turntable. However the much smaller 'TF' grams mass force is transferred via the arm wand to both degrees of freedom arm pivots & onto the turntable.
Magnetic attraction square law force falls off exponentially with linear increases in distance. With two magnets in opposition, a 2015 paper reports at close distances, such as employed in the 'Mag-Lev' tone arm "The magnetic dipole moment is determined from the slope of the magnetic force as a function of the inverse fourth power of the distance."
https://www.researchgate.net/figure/Magnetic-force-as-a-function-of-distance_fig2_272755422
When groove signal vibration displacements are in the positive 'up direction' (“pitching”) the force is in the direction trying to increase the distance between repelling magnets.
This means that due to conservation of energy / forces, such positive 'up direction' groove signal displacements rapidly swap the 'AW' mass coupling route from the magnets (via the arm wand's "yawing" 'side to side' pivot & onto the turntable) to the arm wand (via its "pitching" and "yawing" pivots & onto the turntable).
And in the negative "pitching" 'down direction' the signal acts against increasing magnetic fourth power of the distance forces again up to all of 'AW' mass, but coupled via the magnets (to the arm pivots / turntable).
The same is true whilst following record warps, however they don't excite cartridge suspension / arm wand resonance due to a) magnetic fourth power of the distance damping; b) consequent beneficial non linearity of such damping about zero signal position; and c) no counterweight induced flywheel resonances energy storage release pathways, thereby rendering standard "effective mass" calculations of little if any applicability to Mag-Lev tone arm geometry.
As such, Mag-Lev tone arm's will increase the acoustic impedance at the cartridges' suspension, which will increase fidelity and resolution especially at lower bass frequencies, exactly as reported in listening tests.
"Acoustic impedance is a measure of the ease with which a sound wave propagates through a particular medium."
sound - Impedance | Britannica
Sound waves would be blocked from propagating through a high acoustic impedance medium. Whereas sound waves can propagate freely through a low acoustic impedance medium. Lets picture in our minds an electro-mechanical transducer designed to measure spacial displacements, such as a cartridge cantilever. It has two ends. Since its the difference in displacement between each end that we're trying to measure, one end must be fixed in space. The other end must be free to follow the vibrations. It thus seems appropriate to label the end rigidly fixed in space as a “ground” and the other end as “signal”. If we accept the above definition of acoustic impedance and our transducer labels, then it follows our “ground” must have a “high acoustic impedance”.
In comparison a counterweighted tone arm's mass inertial swings about such a zero signal position (as describe above) are linear, not fourth power of the distance and they are of a far higher amplitude magnified by resonances, thereby why standard "effective mass" calculations must be used to control arm / cartridge suspension resonances, throwing out any possible benefits of increasing acoustic impedance.
'Mag-Lev' geometry advantages are explained succinctly by spladski here:-
Is the magnetic damping (like 2 opposing springs) not only active on the vertical modulation of the signal?
If understood correctly, the horizontal modulation is left undamped, but the cartridge compliance is symmetrical, would this not lead to an imbalance between the horizontal and vertical compliance of the complete system.
A stiffer vertical compliance compared to the horizontal, leading to a different retrieval of the signal than intended.
It is understandable why you might think the standard effective mass calculations are not applicable, but how does damping the vertical modulations make the standard calculation for horizontal effective mass useless? The mass still there, in motion, undamped.
By removing the counterweight mass from the equation, you now possibly have a lower effective mass than what was intended for the cart to retrieve information correctly. I think alighiszem alludes to this.
It does not mean you will not find an audience for this. Linear tonearms have differing compliance in the 2DOF with many adherents, and upon finding an EQ in the chain, eventually everyone starts fiddling with the knobs.
I have no interest in ever hearing it, but that someone went and did this, is good content.
If understood correctly, the horizontal modulation is left undamped, but the cartridge compliance is symmetrical, would this not lead to an imbalance between the horizontal and vertical compliance of the complete system.
A stiffer vertical compliance compared to the horizontal, leading to a different retrieval of the signal than intended.
It is understandable why you might think the standard effective mass calculations are not applicable, but how does damping the vertical modulations make the standard calculation for horizontal effective mass useless? The mass still there, in motion, undamped.
By removing the counterweight mass from the equation, you now possibly have a lower effective mass than what was intended for the cart to retrieve information correctly. I think alighiszem alludes to this.
It does not mean you will not find an audience for this. Linear tonearms have differing compliance in the 2DOF with many adherents, and upon finding an EQ in the chain, eventually everyone starts fiddling with the knobs.
I have no interest in ever hearing it, but that someone went and did this, is good content.
Magnetic damping is active in both directions of the “vertical modulation of the signal” which has an up and a down component (i.e. an oscillation swinging from positive to negative, about zero signal level).
Damping and high acoustic impedance ground coupling (essential for groove vibrations to act against so they can be measured accurately) is achieved by two mechanism a) the magnetic repulsion force working as a function of the inverse fourth power of the distance in the down direction of signal oscillations; and b) arm wand mass coupling to turntable (i.e. acoustic impedance ground) switching between i) via magnets & the side to side pivot in the up direction, and ii) via both pivots in the down direction.
No. Removing the counterweight in itself increases damping as there is much less flywheel effect to store and release energy and resonate. This a big problem with counterweighted arms, hence all the anxiety about tuning an arms “effective mass” with whatever cartridge compliance to avoid such resonance all to easily excited by record warps, and god forbid music low bass frequencies.
So damping in both degrees of freedom in 'Mag-Lev' is achieved by a) significantly reducing the flywheel effect plus b) the magnet derived acoustic impedance ground coupling damping (described above).
See above.
'Mag-Lev' works with a wide range of cartridge compliances because such compliance is not excited into resonance by 'Mag-Lev' arm mass / magnetic repulsion geometry in the same way as resonance is exited in a counterweighed arm.
Thanks for complement, appreciated
I do hope people will build their own 'Mag Lev' just modify an existing arm and give it a go!Meanwhile, my next project is digital room equalisation!
Could you please clarify how a mass is damped, by reducing the mass?
By reducing the mass, you are reducing the inertial resistance to acceleration, how do you equate this to damping?
As far as it goes, yes this is correct. But in a flywheel (i.e. counterweighted tone arm) the inertial resistance to acceleration has a directional component arranged differently relative to its pivot points & gravity (i.e. a damping force) than it is in a pendulum (i.e. Mag-Lev tone arm).
In other words, if we calculate the quantities and directions of the inertia a) relative to another part of the same mass we get a different answer than if b) its calculated relative to a second mass. So first we have to define a reference point to calculate the inertia and its direction relative to that point. This is crucial since its also our reference point used to measure groove vibrations against.
A flywheel has equal mass in all directions out from its pivot, it is balanced in the local gravity field. A tone arm is a special case of a slightly off balance flywheel but arranged as a beam. Yes on both sides of the beam its inertia adds up, but in opposite directions on either side of its pivot. So relative to its pivot a flywheel is designed on purpose to have maximum rotational energy storage / release potential i.e. it is dampened and tends to oscillate. This means that groove vibrations entering at the end of the beam furthest away from the pivot will excite the inertia to oscillate, since such vibrational energy is entering the flywheel at its designed for most efficient energy entry point.
For example, musical instruments such as marimba bars have mass concentrated at each end for exactly the same un-dampened resonance enhancing reason.
harmonic tuning and the marimba
A pendulum of half the mass, in comparison, has no balancing rotational inertia to store / release energy, with reference to its pivot point. It cannot store / release energy in the same efficient mode as a flywheel does.
A pendulum's mass is damped by the local one way gravity field pulling it in one direction of one of its two degrees of freedom ('pitching' down).
A free to swing pendulum will of course oscillate in the one way gravity field. But in 'Mag-Lev' such oscillations are damped on account of the repelling magnets keeping it suspended at 90 degrees to the one way gravity field.
Obviously if we calculate inertia with reference to some other point in space, our flywheel, having twice the mass of our pendulum, also has twice its inertia. But that tells us nothing about its direction relative to the interface between stylus & groove.