| perfusionist |
| What velocity must the cartrige move at in a tangential arm on an LP? What is the formula for determining the ideal weight of a tonearm, given the cartrige weight and compliance? What is the formula describing the arc a pivoting tonearm makes? What is the range, median and average coefficient of friction for a vinyl record? I know the stylus and program material affect it, but there must be a general range. What is the force vector (in general of the groove, in Newtons, pulling a tanegential arm towards the center of the table? Tho horizontal force vector, if you will. If anyonw knows the answer to these questions, I would be greatly appreciative. For those of you without the science. I appreciate your experience too. What tonearm weight would you recommend for a cartridge weighing 5.3 grams, with a compliance of 15 cm/dyn and a tracking force recommendation of 1.8-2.0g |
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| fdegrove |
Hi,
| quote: | | What velocity must the cartrige move at in a tangential arm on an LP? |
None, it's the platter moving not the cartridge...Lest I misread you.
| quote: | | What is the force vector (in general of the groove, in Newtons, pulling a tanegential arm towards the center of the table? |
Again, none. The arm and cartridge are just following the spiral groove of the record.
That's two answers already...:D
Cheers,;) |
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| analog_sa |
Frank
I have the feeling perfusionist wants to know what is the force that the groove is exerting upon the stylus so that it gets pushed towards the centre. His question is obviously not so naive as you make it to be :) And you probably know all the figures he needs.
cheers |
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| sreten |
| quote: | Originally posted by perfusionist
What velocity must the cartridge move at in a tangential arm on an LP? What is the formula for determining the ideal weight of a tonearm, given the cartridge weight and compliance? What is the formula describing the arc a pivoting tonearm makes? What is the range, median and average coefficient of friction for a vinyl record? I know the stylus and program material affect it, but there must be a general range. What is the force vector (in general of the groove, in Newtons, pulling a tangential arm towards the center of the table? Tho horizontal force vector, if you will. If anyone knows the answer to these questions, I would be greatly appreciative. For those of you without the science. I appreciate your experience too. What tonearm weight would you recommend for a cartridge weighing 5.3 grams, with a compliance of 15 cm/dyn and a tracking force recommendation of 1.8-2.0g |
Don't ask much !
a) Depends on the tangential velocity the record was cut.
(for modern records this is variable, depends on amplitude)
b) basically arm effective mass = 1.5 to 2 x cartridge mass.
The compliance stuff you can easily find. add effective mass
to cartridge mass and with compliance you get a frequency.
Ideal frequency is ~ 10Hz, but depends on the type of
suspension and implementation of the turntable.
c) you should be able to find this, depends on overhang and angular offset.
d) no idea.
(the consequences of this are approximately known for
overhung and offset arms, hence their bias adjustment)
e) by definition none, except for the tangential velocity,
consequence is dependent on the compliance of the cartridge.
e) ~ 10g effective mass and specifically a Rega arm.
:) sreten. |
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| sreten |
| quote: | Originally posted by sreten
Don't ask much !
a) Depends on the tangential velocity the record was cut.
(for modern records this is variable, depends on amplitude)
b) basically arm effective mass = 1.5 to 2 x cartridge mass.
The compliance stuff you can easily find. add effective mass
to cartridge mass and with compliance you get a frequency.
Ideal frequency is ~ 10Hz, but depends on the type of
suspension and implementation of the turntable.
c) you should be able to find this, depends on overhang and angular offset.
d) no idea.
(the consequences of this are approximately known for
overhung and offset arms, hence their bias adjustment)
e) by definition none, except for the tangential velocity,
consequence is dependent on the compliance of the cartridge.
e) ~ 10g effective mass and specifically a Rega arm.
:) sreten. |
Note :
all references to tangential velocity ignore lack of concentricity
in the record which is nearly always utterly massively larger.
;) sreten. |
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| perfusionist |
Yes, you are correct, I want to know the forces exerted on an average stylus by an average LP, as force vectors. I am trying to understand the physics of tonearms. Obviously, there is the force of the turntable pushing against the stylus, but the arm pivots when the groove spirals in. There is a horizontal force vector, and that's what I want. If someone knew the angular change of the spiral, that would help.
Regarding tangential tonearms, I want to know what speed to aim for in the linear movement, without haveing to time a record and divide by the distance the tonearm travelled. There must be some audio standard. I want to know what speed the tonearm of a tangential tracks at, the constant velocity. There must be a number, for 33 1/3 rpm.
So an ideal tonearm will have mass 1.5-2.0x the cartrige. What is meant by "effective mass". This would include the mass of everything pivoting, correct?
So ideally, for a 5.3 gram cartridge, the total mass of the arm should be 2.5 to 3 (5.3). Where may I ask did you get this information? I understand that the lighter a tonearm is, the better it tracks the highs, but if too light for the compliance of the cartridge, it will skip. Where can I find scientific monographs on these subjects, I am very interested.
I have also identified some areas of resonance which are problems. I have spoken with several of what are considered the best tonearm manufacturers, and have recieved different answeres.
Some say to get the resonance of the tonearm down to below 4hz, others say to keep it between 5 and 14, others say the critical damping must occur around 20 Hz, and still others say that betweeen 50-150 hz, some tonearms have trouble. |
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| perfusionist |
| I seek all force vectors in Newtons acting on the stylus. For all intensive purposes, that is in two planes. I also seek the horizontal distance/time (m/s) traveled by the cartrige in a tangential turntable as it travels from outside diameter of record to inside. The air tangent tonearm doesnt travel horizontally at 20 mph. It must have a speed, like the turntable does. Also, every curve has a equation describing it. Especially an arc of a perfect circle, like a compass. There must be some equation, involving secants which describes the arc of a pivoting tonearm. |
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| fdegrove |
Hi,
| quote: | | It must have a speed, like the turntable does. |
Yes, it does... the exact same speed as 33.333333 RPM has.
The time it takes to travel from outer rim to inner will be the exact time it takes to play the record. Tangential arm or pivoted/radial arm...
Not so had to comprehend I'd reckon?
Cheers,;) |
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| sreten |
| quote: | Originally posted by perfusionist
Yes, you are correct, I want to know the forces exerted on an average stylus by an average LP, as force vectors. I am trying to understand the physics of tonearms. Obviously, there is the force of the turntable pushing against the stylus, but the arm pivots when the groove spirals in. There is a horizontal force vector, and that's what I want. If someone knew the angular change of the spiral, that would help.
Regarding tangential tonearms, I want to know what speed to aim for in the linear movement, without having to time a record and divide by the distance the tonearm traveled. There must be some audio standard. I want to know what speed the tonearm of a tangential tracks at, the constant velocity. There must be a number, for 33 1/3 rpm.
So an ideal tonearm will have mass 1.5-2.0x the cartridge. What is meant by "effective mass". This would include the mass of everything pivoting, correct?
So ideally, for a 5.3 gram cartridge, the total mass of the arm should be 2.5 to 3 (5.3). Where may I ask did you get this information? I understand that the lighter a tonearm is, the better it tracks the highs, but if too light for the compliance of the cartridge, it will skip. Where can I find scientific monographs on these subjects, I am very interested.
I have also identified some areas of resonance which are problems. I have spoken with several of what are considered the best tonearm manufacturers, and have received different answers.
Some say to get the resonance of the tonearm down to below 4hz, others say to keep it between 5 and 14, others say the critical damping must occur around 20 Hz, and still others say that between 50-150 hz, some tonearms have trouble. |
1) tangential speed is utterly irrelevant - coping with the
eccentricity of records is the engineering problem for
tangential tracking arms.
Related to this the angular change of the spiral is irrelevant.
2) for a pivoted arm with overhang and offset bias force is 0.1
to 0.15 of tracking force at the stylus, can't remember source.
3) effective mass is the mass seen at the stylus tip -
(10g of counter weight is not the same as a 10g cartridge)
- hence tapered tone-arms and decoupled counter weights.
IMO there's no point having a wimpy tonearm if you can help
it, so I discount the plethora of 3 to 5 gram effective mass
arms produced during the V15's heyday. They are ****.
The point is to have good properties without unduly limiting
the compliance of the cartridge to a low value - x 1.5 to 2
for 5g gives a total effective mass of 12.5g to 15g at the tip.
4) the manufactures 'recommendations' ?
4Hz to 7Hz would be a disaster on a suspended subchassis
turntable. 5 and 14 is a very broad version of 10. 20Hz ? I'd
like to see you achieve this with any cartridge I'm aware of.
Tone-arms / turntables can have all sorts of problems further
up the frequency range, really bad ones on poor/cheap designs.
they can have problems 20Hz to 20,000Hz.
:) sreten. |
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| perfusionist |
I am trying to understand the REAL physics involved, and if you cant help me, dont make innane comments. 331/3 is not the horizontal speed of the cartrige, it is the speed of the record. Do you know what force vectors are? the force on the stylus can be broken down into xyz vectors describing the force the record applies to the stylus/cartridge. I want the x! I also want to know the x on a tangential arm. The cartrige on a pivot moves in an arc of a few inches, the record moves 331/3. What I'm getting at is the path of a pivoting arm stylus travels a greater distance than traveled by a tangential arm for the same material. If you travel further in the same time, you are moving faster! Or maybe the pivoting arm takes a bit longer to finish a record? Manufacturers of tangential arms must set the horizontal velocity to some speed? Or does the drag from the stylus pull the tangential arm towards the center?
Both types of arms pass through the same two points in the program material. We know that they pass through the starting point at the same time, but do they pass through the end point at the same time, when one has traveled a farther route? I tend to think the tangential arms track at the same speed of the original cutters, which I dont know and that is what I want to know. The cutter had to be pulled towards the center of the record at a set speed to make the spiral! Does anyone know the formula for this spiral?
So tangential arms move horizontally a tiny bit faster than pivoting arms, and I want to know that speed. I sent questions like this to Japanese cartridge makers, and they seemed to understand me despite the translation, why must you torment me! This is supposed to be a friendly forum where I can get help, not waste my time. I guess I'm going to have to get a record, a ruler, and a tangential arm, and a stopwatch to get some answers. |
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| sreten |
| quote: | | dont make innane comments. |
What about innane questions ?
| quote: | | Manufacturers of tangential arms must set the horizontal velocity to some speed? Or does the drag from the stylus pull the tangential arm towards the center? |
1) no they don't.
2) by definition it can't.
| quote: | | What I'm getting at is the path of a pivoting arm stylus travels a greater distance than traveled by a tangential arm for the same material. |
True, that is a pivoted arm will take ~ 1.5ms longer to play a record.
| quote: | | So tangential arms move horizontally a tiny bit faster than pivoting arms, and I want to know that speed. |
You can work it out from the above, assume distance is 8 cm
and playing time is 20 mins :
V tangential radial= 66.6666667 um/s
V pivot radial = 66.6665833 um/s
V pivot tangental = 16.66666458 um/s
| quote: | | I am trying to understand the REAL physics involved, |
Understanding is being able to ask the right questions.
:) sreten. |
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| Havoc |
Problem with what you define as the "tangential velocity" is that it is dependent on the groove spacing.
When a record is cut, there is chosen a certain distance between the grooves in order to a) make as much music fit on a side as needed and b) make sure there is vinyl between 2 grooves. (okay, not between 2 grooves, but between 2 intersections of the groove at the same radial line if you want to be anal about it). This is done at cutting time.
The last restriction is a result of the dynamic range of the record. To make things worse, there are systems where the distance between the groove is not constant, but depends on the modulation at that moment .
Now, an LP is played at a constant angular velocity. This means that the time it takes for a certain (fixed in relation to the LP) radial to pass under the needle is shorter as you get nearer the hole. SO: the tangential velocity as you call it is not constant! It becomes faster as you get nearer the hole and depends on each record.
So it is not possible to set a fixed tangential velocity for a linear tracking arm. This is probably what you wanted to know. The solution is to let the arm be dragged from rim to center by the force the groove on the stylus or use a feedback system.
Might interest you:
http://www.theanalogdept.com/cartri...rm_matching.htm |
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| sreten |
| quote: | | SO: the tangential velocity as you call it is not constant! It becomes faster as you get nearer the hole |
Sorry but no it doesn't - the groove gets squashed,
you are talking about CD's.
All your other points have already been covered.
I've already said due to eccentricity the TV is a meaningless concept.
:) /sreten. |
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| livemusic |
Hi,
Don't quite understand, why are you interested in lateral speed specifically? There is nothing to do with it, just let the stylus follow the groove, the lathe cutter already did. No doubt, tangential arm does the job more accurately, with nor angular neither overhang discrepancy. The constant speed applies actually no force on stylus (exept friction). The force appears due to speed changes, i.e. acceleration (Newton's law). The third factor in the equation is the arm+cart mass, as it is seen by stylus tip. Effective mass in vertical plane depends of arm's moment of inertia around pivot axle, and should be such as to obtain about 10-12 Hz natural frequency. The lateral effective mass is actually equal to the arm+slider+cart total mass and usually about 30-50 times higher. There is no way to get 10HZ. Poul Ladegaard recommends 2-3 Hz and to apply enough damping to lower the resonant peak. Recently I'm trying to bring the lateral mass to the minimum possible value to get 5-6 Hz lateral frequency to check how it affect the sound.
Good luck with your project! |
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| sreten |
| quote: | | The lateral effective mass is actually equal to the arm+slider+cart total mass and usually about 30-50 times higher. |
this is only true for air bearing tangential arms.
:) sreten. |
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| analog_sa |
Frank
| quote: | | His question is obviously not so naive as you make it to be |
i take my words back :) |
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| innernerd |
As you can see from the other replies to your questions the record itself must dictate to the arm what the tangential speed will be and this will depend on the groove spacing, dynamic range, running time and eccentricity of the pressing to the spindle hole: If eccentricity is bad the arm will track backwards for a while, along its bearing, for each revolution.
Not all parallel tracking arms adopt the same strategy to maintain a constant tangent to the record; they fall into two camps that could be classified as lead and follow:
Those that lead have to either read the record ahead of the pickup arm or provide some sort of mechnical compensation for the inevitable mistracking. An example of a player that reads the record would be the B&O. An arm with mecahnical compensation was the Rabco; it was mechanically linked to the platter but used two pairs of rollers sitting on the driving drum which automatically counteracted any movement of the arm away from the tangent.
Arms that follow the record ideally require a frictionless bearing which when properly implemented has the additional advantage of being very stiff; examples would be the Airtangent and the Kuzma. A non airbearing arm with a roller on wire system, the Souther, is less stiff and has more friction. |
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| Havoc |
| Sreten: You are correct. It does not get faster as you get nearer the center. But it is not constant. It would be only if groove spacing would be constant. And this probably is not. |
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| sreten |
Havoc,
from an earlier post :
| quote: | a) Depends on the tangential velocity the record was cut.
(for modern records this is variable, depends on amplitude)
|
:) sreten. |
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| perfusionist |
| It is my understanging that the tangential arms are motorized. Are you all saying that the groove pulls the whole arm laterally, are you kidding? A pivoting tonearm only moves a small part of its mass laterally. A tangential tonearm moves the entire arm and assembly, and requires a motor. That motor has to be set at a rate of pulling the arm. Anyway, lets just close this thread, as i found the info I wanted. If anyone wants to see what I was after, read the last paper. " Pickup arm design" http://www.helices.org/auDio/turnTable/ If anyone could translate the German paper, I'd appreciate it. I tried with an onlice translator, but it didnt work good. |
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| sreten |
| quote: | Originally posted by perfusionist
That motor has to be set at a rate of pulling the arm. |
If you understood anything thats been said or knew anything
about the characteristics of records in the various ways they
can be cut, and their intrinsic eccentricity you would realise
this is simply not possible.
A motor controlled tangential arm must have some form
of sensor that indicates any deviation from straight,
this implies that it has a horizontal pivot for the arm,
albeit only a small amount of horizontal freedom is needed.
(e.g. fixed LED/lens and receiver, mirror on the arm)
This signal is used by the motor control servo feedback loop
to control the position of the tangential arm base keeping the
arm straight.
Simple as that.
It copes automatically with eccentric records and transverse rates.
Why didn't you just ask how a motor controlled tangential arm works ?
(there are several other types of tangential arms)
:) sreten. |
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| analog_sa |
| quote: | | It is my understanging that the tangential arms are motorized. Are you all saying that the groove pulls the whole arm laterally, are you kidding? |
Hey, what's with the attitude? It is my understanding that you want to learn something, right?
FYI the groove pulls the arm laterally in the air-bearing designs and in the motorised designs a stepper motor moves the arm assembly when needed. From what i remember a B&O unit works like that: the tangential arm is free to rotate at a very small angle; once this angle is exceeded an optical system detects it and a motor moves the arm to a new position. |
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| sreten |
| quote: | Originally posted by analog_sa
the motorised designs a stepper motor moves the arm assembly when needed. From what i remember a B&O unit works like that: the tangential arm is free to rotate at a very small angle; once this angle is exceeded an optical system detects it and a motor moves the arm to a new position. |
Think you'll find that the motor is usually DC, and the optical
system gives a continuous signal, think of a spot moving off a
sensor. The feedback tries to maximise this signal, rather than
an angle being exceeded, giving a continuous analogue DC
servo feedback loop, with much lower error than the above.
:) sreten. |
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| fdegrove |
Hi,
| quote: | The feedback tries to maximise this signal, rather than
an angle being exceeded, giving a continuous analogue DC
servo feedback loop, with much lower error than the above.
|
I can't recall a tangential arm that worked the way described here...
Analog_sa is correct in that in all motorised tangential trackers I know of the arms' lateral movement was allowed some runaway from perfect tangency and than corrected by a servo motor.
Usually this was done by a photoelectric sensor and a motor inside a servo-loop that corrected the tangency error by repositioning the arms' moving assembly as it approaches the innerside of the record.
Examples are the Goldmund T3, B&O, Revox and no doubt some others.
Their predecessor was the old Rabco which was a mechanical design, an evolution of that was the Souther which is still used by Clearaudio, for instance.
Cheers,;) |
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| sreten |
| quote: | | I can't recall a tangential arm that worked the way described here... |
Strange - because we are describing the same thing !
The sensor and feedback loop don't care if its the arm that moves
or the base with the fixed sensor. The end result is the same thing.
My point is its the base that moves to keep the arm straight,
via the feedback loop, of course there must be some lateral
movement of the arm to keep the feedback working,
like the voltage difference between the input pins of
an op-amp due to the open loop gain not being infinite.
The same reasoning applies here.
:) sreten. |
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| fdegrove |
Hi,
| quote: | | Strange - because we are describing the same thing ! |
Sorry, I suppose I just misread you then.
Either way, I don't think those motorised designs are still used or manufactured today.
There are still true air bearing tangential tonearms around though which I find more interesting as a design.
Cheers,;) |
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| perfusionist |
"Now, an LP is played at a constant angular velocity. This means that the time it takes for a certain (fixed in relation to the LP) radial to pass under the needle is shorter as you get nearer the hole. SO: the tangential velocity as you call it is not constant! It becomes faster as you get nearer the hole and depends on each record.
So it is not possible to set a fixed tangential velocity for a linear tracking arm. This is probably what you wanted to know. The solution is to let the arm be dragged from rim to center by the force the groove on the stylus or use a feedback system."
Thank you very much, that's what I was getting at myself. I looked at many tangential tonearms, and they have gearing or motors moving them. I have been reading that website for some time now. I have one more question raised by what you said.
I have been told that the coefficient of friction for an average LP is .3 but it is varied by grooves and stylus shape. Asuming one is using a tangential tonearm, how much weight can a needle drag laterally while following the radial grooves? At what mass does the weight become a problem? |
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| fdegrove |
Hi,
| quote: | | So it is not possible to set a fixed tangential velocity for a linear tracking arm. |
??? To achieve what exactly?
| quote: | | I looked at many tangential tonearms, and they have gearing or motors moving them. I have been reading that website for some time now. I have one more question raised by what you said. |
Really? Anything else I should know?What website? The one with the German language you asked for translation?
I don't mind but be prepared, you have to know what your talking about....From what I read you don't have the foggiest.
| quote: | | I have been told that the coefficient of friction for an average LP is .3 |
I learn everyday, but I don't barge in with an attitude on something I'm asking questions about...
It can be approached differently, you know..............
Cheers, ;) |
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| sreten |
| quote: | | Thank you very much, that's what I was getting at myself. |
Resistance is futile.
:) sreten. |
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| perfusionist |
| quote: | Originally posted by analog_sa
FYI the groove pulls the arm laterally in the air-bearing designs |
If an air bearing arm could be light enough and parrallel to the groove angle, could the groove move the whole arm without servo-motor assitance? |
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| innernerd |
Rockport
Forsell
Air Tangent
Kuzma
Emminent Tech
Dennesen
All these manufacturers think so. |
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| sreten |
| quote: | Originally posted by perfusionist
If an air bearing arm could be light enough and parallel to the groove angle, could the groove move the whole arm without servo-motor assistance? |
Certainly can (assuming the bearing is also very near perfectly level).
Theoretically equates to a lateral displacement of the stylus and
the friction of the bearing, higher compliance cartridges having more
lateral displacement.
Practically the real issue is eccentricity, in records.The arm will be
moving side to side at (for 33rpm) at ~ 0.5Hz. (0.75Hz for 45's).
If the arm friction is low and its very nearly level then this will
dominate the lateral displacement of the stylus.
The lateral arm effective mass and the stylus compliance usually
(assuming friction is low) form a classic underdamped 2nd order
high pass filter.
In this case the higher the compliance/mass resonant frequency the
lower will be the the effective displacement of the stylus from 'true'.
(Assuming the resonant frequency is well above 1Hz)
If the arm is not level it will add a constant DC displacement, the
other enemy is stiction, inconsistent friction, as pure friction to
an extent can be used for a modicum of damping.
Arm/cartridge resonance below around 7-8 Hz is a disaster in
suspended subchassis turntables, and given the levelling
requirements for air bearing arms they do not mix well.
The main advantage of air bearing arms is not the tangentiality -
that goes with the territory - but the theorectically very high
torsional stiffness of the bearing arrangements.
I should also add without the the benefit of any lateral pivot the
lateral effective mass of an air bearing arm is its total moving mass.
Vertical effective mass due to the vertical pivot will always be lower.
:) sreten. |
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| perfusionist |
| quote: | Originally posted by fdegrove
Hi,
Really? Anything else I should know?What website? The one with the German language you asked for translation?
I don't mind but be prepared, you have to know what your talking about....From what I read you don't have the foggiest.
I learn everyday, but I don't barge in with an attitude on something I'm asking questions about...
It can be approached differently, you know..............
Cheers, ;) |
If anyone barges in with an attitude, its you Frank! You make nasty remarks and then have a thin skin when people respond. I am ignorant of the turntable physics, which doesnt allow you the right to insult me.
Your snide little remarks are all over DIYaudio. It's the rare thread where you contribute. Why is your psychology so abnormal?
Why dont you go back to trolling on the DIY TT thread? Maybe becuase the moderator reamed you out for poisining the atmosphere? I guess I'm havent learned your snobby audiophile aloofness. I"m not so knowledgeabel that I can tell people they are wrong, but that " I'm so smart I'm not going to tell them the answer, I'm just going to ridicule you".
You talk so much, yet you say so little. Your caustic comments would be welcome if you could add something constructive, but you post to stroke your own ego. The DIY TT moderator was very tactful in his treatise, but I dont have time for you wasting mine.
I'm sure I could benefit from your knowledge of audio, but you dont care to share, so then just go away.
I cannot find any positive comments you have made, except one... when you thanked someone for a complement! I guess having your ego stroked is all you are looking for, you pathetic little troll. |
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| Havoc |
Calm down a bit. Even if you think that way (and you are entitled to, why not), then there is no reason to get that excited. I understand your anger, but you also have to understand that we tried to get it over to you that what you want -a constant tangential velocity- is not possible. Please try to understand that part also.
Just as a visible indication: http://www.cs.huji.ac.il/~springer/ look at the pictures.... |
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| perfusionist |
Havoc,
In general, you guys have helped me tremendously. If you think I'm acting out of the ordinary, you should look at some of the threads fde has been trolling on. This is his regular mo, and I'm just not in the mood when so many other people are helping me so much.
I understand now that the stylus is constantly accelerating tangentially, but also that its angular velocity is constant. What I realize now Is I'm looking for the angular velocity, which is constant, and a vector quantity. At first, I wanted to make a 10Hz arm which would be pulled by friction alone. Physically, I cant make it light enough to work on a high compliance cartridge.
If I've made a mistake on my calculations, let me know.
I'm wondering if its possible to make a motor whose controler is based on angular velocity, in radians/second, which would speed up proportionately with the tangential velocity. Tangential velocity is proportional to the distansce from the axis of rotation. This would keep the arm constantly accelerating. You see, if tangential velocity is constant, then angular velocity =2*pi*freq (rev/second). Of course, tangential velocity is never constant, but if we make a differential equation using dv/dt as it approches maximum velocity, we can get the constant to set our motor to, which might be very close to what is required for constant acceleration. This it what I'm wondering. If partialdv/partialdt=2pi*freq will work. Angular velocity is constant, no matter where on the radius of a spining mass you are. So if we can use a formula to set the speed of the motor based on that, it should stay tangent without servo-ing.
Of course the speed of the cartridge side is determined by the program material and the coefficient of friction, but if the speed of the back of the arm is well within the boundry of speed changes due to friction reached in a few radians, it might be a simple way instead of all these hysteresis servo systems.
The other problem I had is I'm aiming for 10Hz resonance. As has been pointed out, in tangential arms, the effective mass = actual total mass of arm+screws+wire+counterweight. Using Hz/1000 = 1/2 pi (effective mass x compliance), I solved for the mass of my arm, which could be no more than 3.8-4.2 grams to get 10 Hz. And that's including the counterweight! Even if I could make an arm that skinny, the cartridge (shure v15vx) is 6.3 grams, so the counterweight would have to be way on the other side of thepivot point to lighten that cartridge. I'd go over weight limits before I could cantelever out far enough. I think this is why many tangential arms suspend the cartridge over the surface with a cantilever, to keep the lateral/effective mass down low enough. angular |
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| perfusionist |
| typo, I used hz/1000 = 1/2 pi sqrt (effective mass x compliance) |
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| fdegrove |
Hi,
| quote: | | If you think I'm acting out of the ordinary, you should look at some of the threads fde has been trolling on. This is his regular mo, and I'm just not in the mood when so many other people are helping me so much. |
You sure got a nerve, mister..Trolling, he?
| quote: | | I'm wondering if its possible to make a motor whose controler is based on angular velocity, in radians/second, which would speed up proportionately with the tangential velocity. |
It isn't and it's blatantly obvious why it isn't, unless you have a device watching what's going on. Which is where your controller comes in, which puts you back to square one: feedback controlled devices controlling and correcting errors.
I hope that one helps?
Your little theories are so full of loopholes that I wouldn't know which end to put an handle on them first so just keep on trying: it won't work, that much I can guarantee you.
In fact I've never seen anything like it...Never really looked at a record I suppose?
Cheers,;) |
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| perfusionist |
| No, my idea is NOT to servo, but to have a constantly accelerating motor. Although the variation in grooves changes the speed of the cartridge, if we make a motor finely accelerate so that it cannot overtake the fastest record, yet not undertake the slowest, then there is no need for servo. That is why I asked for coefficient of friction. Frank, I would suggest that instead of always pointing out how much you know and wont share, why dont you show me how smart you are and explain a better way. I challenge you to show my how smart you are. Instead of telling me the many ways my ideas are wrong, why do you not share your ideas, or have you any. Is your only purpose to snipe upon others and not share your vast knowledge? |
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| sreten |
| quote: | Originally posted by perfusionist
No, my idea is NOT to servo, but to have a constantly accelerating motor. Although the variation in grooves changes the speed of the cartridge, if we make a motor finely accelerate so that it cannot overtake the fastest record, yet not undertake the slowest, then there is no need for servo. That is why I asked for coefficient of friction. |
IMO Frank is perfectly entitled to tell you that it won't work.
(And despair at the utterly tortured pseudo logic of the above,
which if analysed does not make the slightest sense whatsoever)
You don't seem to have taken in the information given to you,
simply put again - the problem is the eccentricity of records.
You keep asking questions that seem to blantantly ignore
this fundamental fact, and insist on trying to use concepts that
anyone with an understanding of the way records are cut would
know are far too variable and thus essentially meaningless.
Designing for a 10Hz lateral resonance frequency for a V15 in
an air bearing arm - you've discovered is just not possible.
That doesn't mean it won't work. Your design goal is unrealistic.
As stated before the resonant frequency must be clear of
the 1Hz region. So 2.5Hz to 5Hz is a practical proposition.
:) sreten. |
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| Havoc |
Take a break, and then re-read everything said in this thread (cutting out the non technical bits).
| quote: | | I understand now that the stylus is constantly accelerating tangentially, |
NO! It is not. That was my mistake, corrected by sreten. Tangential velocity is constantly changing! Both accelerating and decelerating!
| quote: | | but also that its angular velocity is constant. |
Yes, that is about the only thing you can be sure of. (come to think of it if you can. Sretens remarks about eccentricity might trow a spanner into that also)
| quote: | | I'm wondering if its possible to make a motor whose controler is based on angular velocity, in radians/second, which would speed up proportionately with the tangential velocity. Tangential velocity is proportional to the distansce from the axis of rotation. |
No. Since angular velocity is constant, it does not give you any information. And it is linear velocity that is proportional to the distance from the axis.
Tangential velocity depends only on:
- program material
- how much running time the engineer wanted on the disc
- mastering proces used
- very probable: label
- very probable: lathe used
So those are the only variables you can use for setting your speed. An arm dragged along by the groove uses those variables. One with feedback just makes sure the variation of tangentiality is within some designed in limits. |
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| sreten |
The tangengial velocity is basically a sine wave of unknown
magnitude at 0.55 Hz or 0.75Hz with a tiny variable d.c. offset.
Thats as much as you can say reliably.
:) sreten. |
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| sully |
I would expect the velocity of the stylus towards the center hole will vary far beyond any constant velocity stylus movement assembly, making the tip bend too far to either side.
I've used 33's that had one song, 5 minutes, one side, with major modulation and groove spacing to accomodate.
And, in between tracks, spacing is large..
Off center holes also.
John |
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| sreten |
| quote: | Originally posted by sully
I would expect the velocity of the stylus towards the center hole will vary far beyond any constant velocity stylus movement assembly, making the tip bend too far to either side.
I've used 33's that had one song, 5 minutes, one side, with major modulation and groove spacing to accomodate.
And, in between tracks, spacing is large..
Off center holes also.
John |
All very true, a constant velocity arrangement will never work,
:) sreten. |
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| fdegrove |
Hi,
| quote: | | Designing for a 10Hz lateral resonance frequency for a V15 in |
With a highly compliant cantilever as the one fitted to the Shure V15 it's not even important: those types of carts hardly throw any energy back into the tonearm....
Low compliance MCs are quite a different story and this is where tonearm design really comes to its' own.
Want to know what your tonearm's worth in that department?
Fit a Decca, you'll know when the sound starts to break up.
BTW, it makes my skin curl when people seem to think it's the cartridge making the movements: it's the arm following whatever's the grooves' pitch is on that record.
Newtons' law on action and reaction gets you a long way to understanding analogue playback very much in the same way Ohms' law does for electronics.
Cheers,;) |
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| sreten |
| quote: | Originally posted by fdegrove
Hi,
With a highly compliant cantilever as the one fitted to the Shure V15 it's not even important: those types of carts hardly throw any energy back into the tonearm....
Low compliance MCs are quite a different story and this is where tonearm design really comes to its' own.
Want to know what your tonearm's worth in that department?
Fit a Decca, you'll know when the sound starts to break up.
BTW, it makes my skin curl when people seem to think it's the cartridge making the movements: it's the arm following whatever's the grooves' pitch is on that record.
Newtons' law on action and reaction gets you a long way to understanding analogue playback very much in the same way Ohms' law does for electronics.
Cheers,;) |
what are you talking about ?
statement 1 is entirely incorrect.
statement 2 is just as bad as compliance per se does not transfer energy.
statement 3 has some basis, the Decca is a difficult cartridge.
statement 4 is just inane.
statement 5 is just wrong.
I'm not going to explain all these points because they don't deserve it.
:) sreten. |
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| fdegrove |
Hi,
Hello???
Cheers,;) |
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| fdegrove |
Hi,
May I suggest you use the quote facility to show your various points?
While I know what mean, you may have difficulty understanding what it is I referred to.
Probably my fault but let's clear the air and get the facts straight.
Cheers,;) |
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| perfusionist |
I am talking about a constantly laterally acclerating motor based on the angular velocity and starting position of the stylus. LPs were known as constant velocity recordings, but they were referring to angular velocity. So if we have a constantly accelerating motor (with respect to angular velocity, time and start position), it will be accelerating constantly with the stylus, and won't it stay parallel? Dont just answer no, explain with physics, I'm trying to understand the physics here!
I do listen to your howls regarding program material and cutting depth, but since you refrenced Newton, Newton says it shouldnt matter at low speeds, even more so at low masses, even more so with kinetic friction of moving objects, which is a fraction of static coefficient of friction. Those forces are being applied at an angle to the stylus, and I have those equations too, also. they are distributed rather evenly with respect to both sides of the stylus, one is lateral I believe and the other depth, so the lateral side (which is it? ) is providing our lateral inward push so to speak.
We have control over where the stylus starts, so we can choose a start point. This gives us a lot of info. We pick a start point with known radius, start time and angular velocity, from which we can also determine the centripital force vector, dependent on radius and mass of arm at that point. Slightly adjusting for stylus friction, we can obtain an equation of a polynomial, the integral of which with respect to time should give position. Using this we can calculate accleration and start velocity. The law of motion in one dimention is this: given position y of the stylus at time t , the derivative of position is velocity....v=dy/dt...derivative of velocity is acceleration a=dv/dt. this is the intantaneous acceleration. This only works if the average velocity is a linear function with respect to time, and I believe it is, because the acceleration is linearly proportional to the square of the radius, so by default, its linear.
So we know the angular velocity and position, giving us the starting velocity of our arm, and we already have the average velocity (if FDE was correct) whose derivative is the instantaneuos acceleration, the rate of acceleration of our arm. For all intensive purposes, our arm will appear to be at constant velocity, except it will be constantly slightly accelerating based on the position the stylus should be at respective to time. Now the problem that has been raised is what if it overruns or lags due to program material.?
Now, you make a great deal about friction, but kinetic friction between moving bodies is almost constant at low speeds. That is why I wanted to know the coefficient of friction, because this can be factored into a more exact equation, a polynomial equation factoring in the average kinetic friction. This will give us a +_error to set our acceleration between, and maybe to adjust on a record to record basis, but only slightly. You audiophiles love to tweak, this will be a joy, different tweak on each record. Just kidding.
Although it varies over time, there exists an average friction, just like and average velocity. Since it is linear, we can use the average for the instantaneous, and calculate the +/- forces to skip and to lag. And given this average over the entire program material, the arm can only be more accurate than a pivot if the motor is placed between these error factors to start with. In fact, the last song, which traditonally has the worst tracking error, would in theory have the best performance with this arm, as the arm should statistically get better with more time played, as the instantaneous variations in values more closely approach the averages.
Taking the force vector normal to the stylus, we can solve for the maximum speed before the stylus jumps the groove at its "slippriest point and maximum angle, and at its highest drag. We can take the derivative of the fastest speed to limit the acceleration of the motor to high and low, and set the acceleration inbetween these two limits. Hopefully, neither will be exceeded before program material ends. The problem with this method is it depends on the mass of the cartridge. This is why I wanted to design for a specific cartridge, to keep that factor in the forces on the stylus constant.
The great question is if the graph of velocity as a funtion of time is a straight line or near it. I believe it is over the vast majority of records, or they would sound very funny. I think over the limited arc of a 33 1/3 record it is, and if the constant acceleration is set up right, one will end the record before the arm outruns or lags the stylus. The benefits of better tracking would outweight the few times this error would occur. Comments? It is given that these equations only work if I can calculate an average velocity. But remember that Keppler and Newton found these equations to work with planets, which are far larger and faster than LP's ;) And that is where your many comments about record variation may have some merit, but those are anecdotal observations, not empirical. I want to know the force vecors acting on the arm. The velocity we are referring to is solved for by the equation for centripital force Fc= mv2/r where v2/r is the centripital acceleration. given position y of the stylus at time t , the derivative of position is velocity....v=dy/dt...derivative of velocity is acceleration a=dv/dt. this is the intantaneous acceleration.
I now believe the gaps between songs are a bigger problem than the kinetic friction. The lack of friction will introduce more errors than program material. Are those gaps standardized? Here is the argument that friction varies so much. If the modulation was such a problem, your records would have lots of WOW before the average velocity varied so much from record to record, and you would notice it. Or they would skip. For all intensive purposes, we can hold the coefficient of friction constant.
I'll finish this later. You guys have got a great discussion going on now. Thanks for getting back on topic. You too, FDE, even if you need to go back to your physics book, you're trying to be constructive. |
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| analog_sa |
| quote: | | at its "slippriest point |
If i may ask a question: what's the point of all this? A mental exercise of a retired physics teacher? Surely you'd do much better to examine the designs of the leading tangential arm manufacturers and suggest improvements. None of them are motorised btw. |
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| perfusionist |
| quote: | Originally posted by Havoc
Sreten: You are correct. It does not get faster as you get nearer the center. But it is not constant. It would be only if groove spacing would be constant. And this probably is not. |
Actually I think you are both correct, the grooves get tighter, and it accelerates towards the center quicker because of the higher frequency of the tighter grooves.
there is no point to this, just learning about turntable physics. |
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| Havoc |
I'm giving up.
| quote: | | LPs were known as constant velocity recordings, |
There has been a time -long ago- when there were constant velocity recordings. BUT THIS REFERRED TO THE MODULATION OF THE GROOVE! Not the spacing of the grooves.
If you start from wrong premises you end up nowhere.
| quote: | | While I know what mean, you may have difficulty understanding what it is I referred to. |
Frank, can you cut all those wise-cracks and explain for everybody whatever you are talking about? If you don't like to be adressed as a troll, you better explain or shut up. If you know what you are talking about and then share your knowledge -as supposed on a forum- but stop implying that everybody is an idiot. |
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| Paul Ranson |
It's obvious that it isn't possible to track a record with an arm moving constantly inward, even at a rate related to the distance from the inner groove.
'perfusionist' could estimate how large an error between the arm position and the stylus can be allowed to build up before performance suffers, and how much the cutter might vary the groove pitch during loud passages.
We would have to preplay each record with a measuring device to determine how to drive our pickup arm. At the moment I'm not seeing the benefit...
By contrast the physics that allows a conventional radial pickup to produce output yet move inwards with the groove and track warps and eccentricity without generating significant output would appear quite approachable.
Paul |
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| sreten |
perfusionist :
I'm giving up on you.
You seem to not want listen or be interested in any salient fact
that inconveniently does not suit your way of seeing things.
And when needed conveneniently make up assumptions that
are wrong justified by incoherent arguements, as the assumptions
are wrong so are the arguements.
Consequently your rambling musings compound one error
after another, you don't seem to care they do not make any
practical sense whatsoever.
I wouldn't let you fix my car........Or get into a car you built.
Frank :
| quote: | | With a highly compliant cantilever as the one fitted to the Shure V15 it's not even important: those types of carts hardly throw any energy back into the tonearm.... |
a) Having the correct arm resonant frequency is important,
especially for suspended subschassis turntables.
b) high complinance cartridges with low tip mass still throw a large
amount of energy back into the arm, only a few dB less than a
good moving coil.
| quote: | | Low compliance MCs are quite a different story and this is where tonearm design really comes to its' own. |
Not in my experience. the type of cartridge does not matter.
Effective tip mass and generator damping seem to be more
important issues.
| quote: | | Want to know what your tonearm's worth in that department? Fit a Decca, you'll know when the sound starts to break up. |
Which illustrates my point above.
| quote: | | BTW, it makes my skin curl when people seem to think it's the cartridge making the movements: it's the arm following whatever's the grooves' pitch is on that record. |
Assuming the cartridge is bolted to arm what diiference does it make ?
| quote: | | Newtons' law on action and reaction gets you a long way to understanding analogue playback very much in the same way Ohms' law does for electronics. |
I simply disagree with this as its far too simplistic.
Transmission line theory helps a lot IMO.
;) sreten. |
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| fdegrove |
Hi,
| quote: | | With a highly compliant cantilever as the one fitted to the Shure V15 it's not even important: those types of carts hardly throw any energy back into the tonearm.... |
| quote: | | a) Having the correct arm resonant frequency is important,especially for suspended subschassis turntables. |
For high compliance suspensions such as used by Shure it isn't critical.
You can compare them to the suspension of a typical American automobile if you like.
What does the TT suspension have to do with tonearm resonance?
| quote: | | b) high complinance cartridges with low tip mass still throw a large amount of energy back into the arm, only a few dB less than a good moving coil. |
Almost any MM cartridge will have a tip mass that's much higher than modern MCs.
The cantilevers are more often than not very crude affairs that are basically preformed hollow pipes with a flattened end where the diamond is pressfit.
| quote: | | Low compliance MCs are quite a different story and this is where tonearm design really comes to its' own. |
| quote: | | Not in my experience. the type of cartridge does not matter. |
See above.
| quote: | | Want to know what your tonearm's worth in that department? Fit a Decca, you'll know when the sound starts to break up. |
| quote: | | Which illustrates my point above. |
Why?
If you know that a Decca cart. hardly has any cantilever to speak of and that it's mounted nearly vertically and hardly has any suspension at all, you'll realise the amount of energy that's thrown back into the arm and cartridge body.
Any Decca owner will confirm that.
| quote: | | Assuming the cartridge is bolted to arm what diiference does it make ? |
The difference is that when we discuss tonearms it's confusing to follow what's meant when people add catridges into the equation.
Which is why no tonearm designer I know off will refer to catridge movements when explaning his design rationale.
| quote: | | I simply disagree with this as its far too simplistic. |
Of course it is but people have to start somewhere...
| quote: | | Transmission line theory helps a lot IMO. |
Sure does, as does a number of other items such propagation of soundwaves in various materials...
Anyway, let's return to linear trackers before we have to start yet another thread on TT and tonearm design...:D
Cheers,;) |
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| fdegrove |
Hi,
| quote: | | It's obvious that it isn't possible to track a record with an arm moving constantly inward, even at a rate related to the distance from the inner groove. |
Indeed it isn't possible with a motorised device moving inwards at a constant speed.
The result would be a stylus skipping the grooves as the arm moves, at best, or at worst a broken cantilever.
Other than the common airbearing designs which suffer only from a high horizontal mass, there are a few mechanical designs such as Souther (Clearaudio) and the Paragon by Nottingham Analogue.
Once setup for correct tangency they track the record exactly as it was cut.
A pivoted arm, no matter how well designed only approaches tangency at two spots on the record if you're lucky.
Cheers,;) |
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| perfusionist |
Sreten and Havoc,
I've found your posts to be the most informative, didnt mean to turn you off. I have learned a lot from both your posts, thanks.
Probably the reason my ideas are from the old days are I did my homework, I read all the original papers on tonearms but the papers I have read are 30-50 years old, so many new ideas I'm sure you know but I dont. That's why I ask for your patience as I learn and get up to speed. I didnt realize that most air arms were not motorized, I dindnt know the stylus could pull that much mass along the track.
Given a coefficient of .3 and a cartridge compliances of 15 and 25, can anyone estimate the maximum mass, beyond which the performace of a tangential passive (non motor) air arm will suffer due to too much effective mass? We know that effective mass = actual mass in an air tangential. What would be an ideal mass?
Also, why are longer radial tonearms no longer popular, is it simply for convenience, as they track 25% better. |
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| Havoc |
| quote: | | can anyone estimate the maximum mass, beyond which the performace of a tangential passive (non motor) air arm will suffer due to too much effective mass? |
Check the Ladegaard design, if I remember well, then he added about 300g to the cart without any problems.
| quote: | | Also, why are longer radial tonearms no longer popular, is it simply for convenience, as they track 25% better. |
Don't know. Just a guess:
- mass, they are larger
- size, not everybody is charmed by a 1m arm
- setup, you need a lot of space and if you want to mount the arm onthe same base as the platter it can become a problem
- fashion, hifi is a lot about fashion, you can deny it and/or not like it, but it is that way. |
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| fdegrove |
Hi,
| quote: | | I dindnt know the stylus could pull that much mass along the track. |
Actually the stylus isn't pulling anything, it just follows the spiral groove as it passes beneath it at the given platter speed (331/3 or 45 RPM.
| quote: | | Also, why are longer radial tonearms no longer popular, is it simply for convenience, as they track 25% better. |
The reason the 12' arms were preferred is not because they track better but that they had smaller offset error.
They're not popular with MC cartridges because their length augments their resonant frequency.
Cheers,;) |
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| perfusionist |
| quote: | Originally posted by fdegrove
Hi,
Actually the stylus isn't pulling anything, it just follows the spiral groove as it passes beneath it at the given platter speed (331/3 or 45 RPM.
The reason the 12' arms were preferred is not because they track better but that they had smaller offset error.
They're not popular with MC cartridges because their length augments their resonant frequency.
Cheers,;) |
The question was what's the maximum horizontal mass WHATEVER force is moving it, that an air arm can carry, you know what the hell I'm asking! |
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| fdegrove |
Hi,
| quote: | | The question was what's the maximum horizontal mass WHATEVER force is moving it, that an air arm can carry, you know what the hell I'm asking! |
Since you so politely ask:
Obviously as light and rigid as you can possibly make it.
Cheers,;) |
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| perfusionist |
| quote: | Originally posted by fdegrove
Hi,
Since you so politely ask:
Obviously as light and rigid as you can possibly make it.
Cheers,;) |
First, the answer shoud be in grams, not your vague guidelines with no direction, useless response. I believe it was Havoc who said 300 grams. What dont you understand about my question, and why do you play your little games, cheers?
What is it about the maximum possible mass that you dont understand FDE? You understand english worse than the Japanese engineers I wrote? I think not. Aren't you Flemish?
Trolling once again, not being helpful. You are obviously wrong as well, because as "light as possible" could put it into a bad resonant frequency. Perhaps this is why Air Tangents is heavier, to go below the bad freqencies. 2-4 is much better than the worst 5-8. And very light tonearm will get to 5-8. It must be either extremely light or heavier. In between makes a bad resonant frequency.
I made it so light that the resonance was around 6 hz, It would encourage record wobble. |
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| fdegrove |
Hi,
| quote: | | First, the answer shoud be in grams, not your vague guidelines with no direction, useless response. |
How can it be given in grams when this has to be viewed within the concept of the entire design.
| quote: | | You are obviously wrong as well, because as "light as possible" could put it into a bad resonant frequency. Perhaps this is why Air Tangents is heavier, to go below the bad freqencies. 2-4 is much better than the worst 5-8. And very light tonearm will get to 5-8. It must be either extremely light or heavier. In between makes a bad resonant frequency. |
No, I'm not wrong but like anything else in this world you need to strike the best set of compromises within your design aims.
BTW the ATs are very light once you remove the counterweight. They're made out of magnesium ( the armtube) and titanium ( the slider).
In order to dampen any resonances they're fitted with a damping trough which is filled with silicone oil.
The armtube has additional damping properties by its tapered shape and has a stepped multilayer of heatshrinks to further damp out resonance.
Cheers,;) |
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| sreten |
I really don't know where this thread is going.
As its a DIY forum the point is surely some practical realisation
of a problem and the most sensible design approach to make
it work as best as possible.
I just don't see that here at all.
People are just arguing about stuff because they are
never going to build it - as they say talk is cheap.
As a DIY forum this is not the place for theorectical ramblings,
the proof of this being the biggest threads here are the most
useless, cable directionality, the sound of mains leads etc.
Is Perfusionist actually going to make a parrallel tracking arm ?
If not this is never going to get anywhere.
:) sreten. |
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| fdegrove |
Hi,
| quote: | | As a DIY forum this is not the place for theorectical ramblings, |
Well, I wouldn't go that far...
However, I do wish people made more effort preparing their discussion. In that way QQ are more ad rem and don't need any second guessing.
Btw, I don't mean you at all Sreten.
If someone wants to build their own LT then the Poul Ladegaard designs are a good place to start.
Some members have already posted their Ladegaard clones here so I see little point in rehashing that any further.
OTOH, if someone wants to copy a LT such as the AT then I won't contribute for obvious reasons but I don't mind explaining the reasoning behind the design.
Accusing people of trolling isn't go to help though, I have better uses for my time...:smash:
Cheers,;) |
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| Havoc |
| Thought a bit more about that horizontal mass. It does not matter much. The only load the cartridge is "pulling" is not the horizontal mass, but the force made by that horizontal mass and the friction coefficient of your air-bearing. And that last one is very very low. |
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| Paul Ranson |
You still have a mass (the total moving mass of the arm) and a spring (the horizontal compliance of the cartridge. That means you have a resonance. It will be at a low frequency compared to the resonance with a radial pickup. Whether that matters is down to the engineering...
Paul |
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| fdegrove |
Hi,
The effective horizontal mass becomes important when dealing with record eccentricities.
Cheers,;) |
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