Turntable physics questions-velocity of tangential arm?
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 17th December 2003, 09:11 PM #1 perfusionist   diyAudio Member   Join Date: Oct 2003 Location: Tejas Turntable physics questions-velocity of tangential arm? 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
fdegrove
diyAudio Senior Member

Join Date: Aug 2002
Location: Belgium
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.

Cheers,
__________________
Frank

 17th December 2003, 09:55 PM #3 analog_sa   diyAudio Member     Join Date: Aug 2002 Location: Cascais 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
sreten
R.I.P.

Join Date: Nov 2003
Location: Brighton UK
Re: Turntable physics questions-velocity of tangential arm?

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

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.

sreten
R.I.P.

Join Date: Nov 2003
Location: Brighton UK
Re: Re: Turntable physics questions-velocity of tangential arm?

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.

 17th December 2003, 10:49 PM #6 perfusionist   diyAudio Member   Join Date: Oct 2003 Location: Tejas 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.
 17th December 2003, 11:08 PM #7 perfusionist   diyAudio Member   Join Date: Oct 2003 Location: Tejas 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.
fdegrove
diyAudio Senior Member

Join Date: Aug 2002
Location: Belgium
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,
__________________
Frank

sreten
R.I.P.

Join Date: Nov 2003
Location: Brighton UK
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 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.

 18th December 2003, 12:56 PM #10 perfusionist   diyAudio Member   Join Date: Oct 2003 Location: Tejas 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.

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