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
perfusionist said:
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.Re: Re: Turntable physics questions-velocity of tangential arm?
Note :
all references to tangential velocity ignore lack of concentricity
in the record which is nearly always utterly massively larger.
sreten.
sreten said:
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.
Note :
all references to tangential velocity ignore lack of concentricity
in the record which is nearly always utterly massively larger.
sreten.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.
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.
To fdegrove
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.
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.
perfusionist said:
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 crap.
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.tangential speed
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.
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.
What about innane questions ?
1) no they don't.
2) by definition it can't.
True, that is a pivoted arm will take ~ 1.5ms longer to play a record.
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
Understanding is being able to ask the right questions.
sreten.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/cartridge___arm_matching.htm
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/cartridge___arm_matching.htm
Arm effective mass
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!
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!
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.
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.
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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