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In Reply to: Again this is simple..... posted by tubesforever on September 11, 2006 at 12:10:26:
Are you saying you've modelled how a beam formed by an armtube, cartridge and countweight behave when excited by a 15Hz resonance or impulse imparted by a record warp?It is indeed simple; a cartridge exerts torque on the arm tube which acts agains any other force rting to deflect (rotate) the beam from vertical.
A C/W whose mass is split equally above and below the fulcrum (i.e./e.g. a circular concrentric one on a Rega, but not if it were on an SME)) doesn't exert any such torque.
It is 'intuitively' right that the C/W should also hang and provide a similar centering torque to the cartridge.
To reiterate, the problem is the unwanted variations in VTF an underslung C/W inflicts on a beam-centred pivot/fulcrum arrangment.
A compromise is needed (or a suspended 'smart' C/W), hence the Tecnoweight and my proposed DIY variation.
Follow Ups:
So even with a 60hz electric bass riff, the needle is accelerating upwards in the groove pushing up against the cartridge. On your underhung model it is lowering the effective mass at the cartridge and reduces the vtf.A warp or dish would create more visual excitations.
By centering the median mass of the counterweight in the same plane as the stylus you are providing the minimal vtf fluxuation and gaining the highest tracking.
The software we are running is extremely powerful. It is configured on a 128 bit unix processor and we can examine extremely minute stylus movements and see what it does to the EM at the cartridge interface.
I started exploring this because I could not understand why my Grado Ref Master had such significant sibilence on a medium massed tonearm, and reduced on the Magenepan Unitrac low mass tonearm.
It was the effective mass at the cartridge and the compliance of the stylus related to the inertial moment of the tonearm which improved tracking.
....consider the role of 'outigger' weights - they apply no 'rotational' torque (assuming theyre not underslung) to the beam, but do add effective mass in that moment (but also to the 'yaw' moment, (i.e. lateral movement) of the arm which we also don't want, ideally).I wonder if a very wide 'dumbell' shaped (non-underslung) C/W would be worth trying.
There is a definite improvement of the inertial moment if the median of the mass is very tightly specified. Meaning keeping the weight flat vs a cylindrical or dumbell shape. To minimize distortion of the stylus it is critical to balance that counterweight to the cartridge not to the bearings. So the outrigger on the SME is an interesting test for this model at this time.I think I argued once with JD and asked John Elison for some input, because with my Grado Ref Master I could not use the outrigger as a vtf adjustment. It had to be used for balancing the arm.
JD really jumped on me for this....but it was specific to the Grado Ref Master and I did not mean for this to be a universally repeatable phenomena.
This is all theory since I have yet to test a thing in the real world. My guestimate is that it will sound great to my ears because I cannot afford an excellent Graham, SME, or Schroeder to compare it against.
Listening at a CES show is definitely not proof of anything I rarely get any kind of seat where I can hear the soundstage imaging.
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