The round tube that runs front to back down the middle of that SX68 is called the 'torque tube' and is held at the back by a length of piano wire thru a hole in the backplate, essentially a flexture. This tube takes the force from dragging the cutting stylus thru the lacquer back into the body of the head and prevents it from being applied to the voice coil assemblies.
This is the cantilever in the cutting head.
The elastomer damping at the back is basically to reduce high frequency reflections in the torque tube as the feedback is becoming less effective as frequency rises into the low ultrasonic.
One major difference between a feedback head (The SX68) and the other experimental ones shown there is that the feedback head is mechanically very underdamped in order to get better sensitivity and reduce the stupid amount of power needed to cut at high frequency (professional cutting amps are good for 500W or so, and the voice coil in that SX68 is less then 10mm in diameter).
Open loop heads are typically designed with far more damping to make something that can be reasonably equalised open loop, but getting such a design to work at above 10kHz is tricky because of both resonances and the damping causing massive power requirements (and heating).
On the subject of stylus geometry and crap record players, there is a tradeoff to be made by the cutting engineers, because you can at very high frequency cut something that cannot be played back on a spherical stylus but can be played back on a line contact/super elliptical/<whatever>.
With the modern market being what it is the pressure is generally to cut something that will track on a crap deck with a worn stylus, this is essentially a commercial decision and may well be played differently if you are a classical label to if you are cutting for the supermarket vinyl shelf.
I would note that each stylus geometry will generally track at a different depth in the groove, which can be useful if you have very worn vinyl as switching to a different geometry can get you some more life.
Oh Ref post 45, don't forget that the cutter is also tilted with respect to the disk surface, and (due to spring back) this angle is NOT the same as the cantilever angle on playback (And is also not at all well standardised).
Finally, remember that the Neumann approach is NOT the only way to cut a stereo disk, Ortophon had something quite different in terms of head geometry, and while it had a bad reputation for being delicate (Even by the standards of these things), it did work and did NOT have a cantilever at all in the classical sense.
This is the cantilever in the cutting head.
The elastomer damping at the back is basically to reduce high frequency reflections in the torque tube as the feedback is becoming less effective as frequency rises into the low ultrasonic.
One major difference between a feedback head (The SX68) and the other experimental ones shown there is that the feedback head is mechanically very underdamped in order to get better sensitivity and reduce the stupid amount of power needed to cut at high frequency (professional cutting amps are good for 500W or so, and the voice coil in that SX68 is less then 10mm in diameter).
Open loop heads are typically designed with far more damping to make something that can be reasonably equalised open loop, but getting such a design to work at above 10kHz is tricky because of both resonances and the damping causing massive power requirements (and heating).
On the subject of stylus geometry and crap record players, there is a tradeoff to be made by the cutting engineers, because you can at very high frequency cut something that cannot be played back on a spherical stylus but can be played back on a line contact/super elliptical/<whatever>.
With the modern market being what it is the pressure is generally to cut something that will track on a crap deck with a worn stylus, this is essentially a commercial decision and may well be played differently if you are a classical label to if you are cutting for the supermarket vinyl shelf.
I would note that each stylus geometry will generally track at a different depth in the groove, which can be useful if you have very worn vinyl as switching to a different geometry can get you some more life.
Oh Ref post 45, don't forget that the cutter is also tilted with respect to the disk surface, and (due to spring back) this angle is NOT the same as the cantilever angle on playback (And is also not at all well standardised).
Finally, remember that the Neumann approach is NOT the only way to cut a stereo disk, Ortophon had something quite different in terms of head geometry, and while it had a bad reputation for being delicate (Even by the standards of these things), it did work and did NOT have a cantilever at all in the classical sense.
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The Ortofon Rocking Bridge approach is described in
Disc-cutting lathes
It is claimed that they were the choice to pair with sister company Lyrec cutting lathes.
Another simple question (well, several naive questions):
how, and where, is needle talk generated?
We all know the incredible stresses (accelerations, point loads) that are the basis of the tracking, but how to model / calculate such a complex system?
I imagine the stylus - cantilever - magnet (or iron or coils) system as a kind of seismic (i.e. not subject to gravity) physical pendulum, more or less balanced - L1M1 = L2M2 -, oscillating on a fulcrum (elastomer)
First question -- what is the period of that pendulum? does it have any influence on tracking movements?
Second question -- if the resistance of the constraint would be zero there should be no resultants on the fulcrum (no needle talk). But obviously this is not the case of our elastomer. Korff on his site proposed interesting hypotheses of possible deformations (in addition to the oscillation I would also add the traction exerted by the SD). But how to calculate the solicitations transmitted to the cartridge body? are they relevant as presumed?
Third question -- ideally the work resulting from tracing is converted to electromotive force (personally I have measured large variations of the SD in relation to the musical content). But to what extent (SD/mV ratio)? and how to calc this? and in addition to degeneration into heat, is there also some stress - attraction repulsion - of the generator, ( ie cartridge body) combined with the stresses from the elastomer?
Forgive my confusion - I searched on web, finding just authoritative opinions on how good a wooden vs plastic cartridge body sounds; or vice versa. Hoping that who knows more than me, that is everyone, could explains us the answers. Not without consequences, just to mention a few: better high or low compliance? better light or heavy cartridge / headshell? stiif or elastic wand? etc etc.
carlo
Sorry if offtopic
how, and where, is needle talk generated?
We all know the incredible stresses (accelerations, point loads) that are the basis of the tracking, but how to model / calculate such a complex system?
I imagine the stylus - cantilever - magnet (or iron or coils) system as a kind of seismic (i.e. not subject to gravity) physical pendulum, more or less balanced - L1M1 = L2M2 -, oscillating on a fulcrum (elastomer)
First question -- what is the period of that pendulum? does it have any influence on tracking movements?
Second question -- if the resistance of the constraint would be zero there should be no resultants on the fulcrum (no needle talk). But obviously this is not the case of our elastomer. Korff on his site proposed interesting hypotheses of possible deformations (in addition to the oscillation I would also add the traction exerted by the SD). But how to calculate the solicitations transmitted to the cartridge body? are they relevant as presumed?
Third question -- ideally the work resulting from tracing is converted to electromotive force (personally I have measured large variations of the SD in relation to the musical content). But to what extent (SD/mV ratio)? and how to calc this? and in addition to degeneration into heat, is there also some stress - attraction repulsion - of the generator, ( ie cartridge body) combined with the stresses from the elastomer?
Forgive my confusion - I searched on web, finding just authoritative opinions on how good a wooden vs plastic cartridge body sounds; or vice versa. Hoping that who knows more than me, that is everyone, could explains us the answers. Not without consequences, just to mention a few: better high or low compliance? better light or heavy cartridge / headshell? stiif or elastic wand? etc etc.
carlo
Sorry if offtopic