Tonearm Setup: Effective Mass, Inertia, and Sound

I have been experimenting with adjusting my tonearm's counterweight. I can add or remove extra weights and slide the counterweight mechanism toward or away from the pivot point of my arm. One can see from the three photographs below how the extra weights change the size of the counterweight, lower its center of gravity, and alters its position relative to the arm's pivot point.

I am curious how these changes may or may not affect the overall effective mass of the arm and the moment of inertia of the system. I would think these properties would interact with the cartridges compliance to change the sound. I assume that the added weight near the pivot also loads the arm's bearing to a greater extent which may affect the way resonances travel through and escape from the arm into the arm base.

Has anyone else done such experiments with his arm? Do you hear any differences? Is there a theoretical advantage to one position or another? As with the recent cartridge loading thread, it was fascinating to learn about the theory of cartridge loading, but in the end, final settings are often done by listening. I suspect that this may also be the case with these adjustments because of their interaction with the cartridge.

I do hear slight differences, but I'd like to start a discussion about this topic before describing what I hear.

 

yes, 3 different cartridges, three separate arms, but always consistent.

OTOH........my last 3 'long term use cartridges (Ortofon Anna, GFS, and the Anna Diamond) all weigh the same, 16 grams. all are low to medium compliance. Durand Telos, Sapphire Telos, and Tosca are medium mass tone arms. the Anna was used in development of both tonearms.

i respect that maybe my experience has been fairly narrow over the recent years. so what looks like a general rule might just be my little corner.

 

with my Durand Telos Sapphire tone arm it was always very important to use the largest weight close to the pivot as opposed to a smaller weight farther away.

the Telos used special 'unobtainium-metal' weights (denser and heavier for their size) which were a clear step up over the standard Telos weights. i now use those special Telos weights on my Tosca. (the standard Tosca weights are lighter for their size). these weights made a clear positive difference in the bass slam and energy projected. so maybe it's not just the weight and location, but also the density and focus of that weight that matter.

after i got my Clearaudio GFS (fairly heavy) Joel had a special longer weight made (not cheap) which took the place of using 2 weights. this could be a little closer to the pivot and also as a single weight was better. this longer weight works on the Telos, but not the Tosca.

i feel like more of an observer of cause and effect, than really understanding exactly why things happen. on some level i have some feel for the forces involved, but try to not just do things because i (think i) know they are better, but because i can hear that they sound better.

Could you also attribute the material of the counterweight to contribute to better sound.

 

Could you also attribute the material of the counterweight to contribute to better sound.

yes, that is what i hear. maybe not so much the material, but it's particular density and mass.

but the concept of closer to the pivot point sounding better also worked for the standard weights too.....in my experience.

 

yes, that is what i hear. maybe not so much the material, but it's particular density and mass.

but the concept of closer to the pivot point sounding better also worked for the standard weights too.....in my experience.

Maybe it also help anchor the bearing down better, especially unipivot and knife bearing arm that rely on mass to help keep these types of bearings seated.

 

Changing the position of the conterweight will of course change the Inertial moment so also the FR of tonearm/cartridge and the sound will change (then we will choose the one we prefer).
Anyway the closer the conterweight will be to the pivot, the less inertial moment we will have.

 

I was emailing with a cartridge designer at Too Wing recently, and in the course of that discussion, he mentioned the very same things we've talked about in this thread. Regarding Blue Dragon vs Red Sparrow:

You can use both cartridges with your tonearm from the point of view
of the resonance frequency.
The Red Sparrow might be better but the resonance frequency would be
changed by a position of a counter-weight, or the tonearm's design.
As other factors, there is a difference in their sound characters by
their body materials.

 

I have been experimenting with adjusting my tonearm's counterweight. I can add or remove extra weights and slide the counterweight mechanism toward or away from the pivot point of my arm. One can see from the three photographs below how the extra weights change the size of the counterweight, lower its center of gravity, and alters its position relative to the arm's pivot point.

I am curious how these changes may or may not affect the overall effective mass of the arm and the moment of inertia of the system. I would think these properties would interact with the cartridges compliance to change the sound. I assume that the added weight near the pivot also loads the arm's bearing to a greater extent which may affect the way resonances travel through and escape from the arm into the arm base.

Has anyone else done such experiments with his arm? Do you hear any differences? Is there a theoretical advantage to one position or another? As with the recent cartridge loading thread, it was fascinating to learn about the theory of cartridge loading, but in the end, final settings are often done by listening. I suspect that this may also be the case with these adjustments because of their interaction with the cartridge.

I do hear slight differences, but I'd like to start a discussion about this topic before describing what I hear.

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Can you give me some details on this extra counterweight please?

I am considering an Audio Note UK IO Gold cartridge but the beast is 20g and would barely balance in my SME V.

 

Pay attention to declared compliance. 8Cu at which frequency? Usually Japanese producer declare their compliance at 100 Hertz, so at 10 Hertz real compliance could be much higher (around 15/16 cu).
So the RF of the system could be around 8/8.2 Hertz.
To verify i think could be helpful a test record.

Well compliance is rated in units of mm/N. What this means is: if I have a compliance of 8 mm/N, if I apply a force of 1 Newton to the stylus, it will deflect by 8mm. 1 Newton is a fair amount of force here. A more practical weigh to think about it: this cartridge's stylus will move by ~ 1/2 mm if I apply a force equivalent to the weight of a quarter coin (USD!). If you think of a spring, it is the same exact idea. It does not depend on frequency.

 

Can you give me some details on this extra counterweight please?

I am considering an Audio Note UK IO Gold cartridge but the beast is 20g and would barely balance in my SME V.

My SME V-12 had extra weights to insert for heavier cartridges.

 

Can you give me some details on this extra counterweight please?

I am considering an Audio Note UK IO Gold cartridge but the beast is 20g and would barely balance in my SME V.

SME V can handle cartridges up to 14g. SME V has an effective mass of 10,5g. It’s relatively low. If you use a 20g cartridge which has very low 5 - 10 µm/mN compliance then you may exprience tracking problems with SME V. It’s like putting truck suspension to a sedan.

I recommend to use a heavier arm instead or another cartridge.