Merits of Heavier Arm Counterweights

Colinjg

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Apologies if this has been covered before.

I am intrigued by the physics of why a heavier counterweight would be an advantage sonically, in the light of the light of the number being sold and marketed. Clearly if you have a heavy cartridge and you run out of adjustment then it is a no brainer.

I would be interested if anyone could contribute as to why it would be an advantage or whether there is something I have not thought of. Before Christmas I spent a good half hour  plus discussing this with an old friend over a long walk who has a serious Maths and Engineering Degree, plus 40 years in Mechanical Engineering compared to my lowly A Level Physics grade which I somehow managed. We could not reach a conclusion, BUT,

Assuming arm rigidity, you can argue that a stylus would not be able to "see" any difference between a heavier mass nearer the pivot point compared to a smaller mass further away. The effective mass would be identical.

What does change is the total mass of the whole arm and the total mass of the arm behind the pivot point. The increase in total mass would put slightly more weight on the arm bearing, (not necessarily a good thing) which might behave slightly differently. But, the mass the stylus is exposed to would be effectively the same.

Can somebody advise please if there is something I am missing, ( there usually is).  I suspect Newton and inertia might be involved??

If I am talking complete *******s I will retreat back into my hole.

Cheers. C.

 

SergeAuckland

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Using a heavier counterweight has several advantages/features:-

1) A heavier counterweight needs to be closer to the pivot point, and so reduces the overall arm mass. This may or may not be an advantage, but generally, if one needs to adjust the overall arm mass as seen by the stylus,it's a lot easier and more precise to load mass onto the headshell (or use a heavier headshell) if needed, than to try and adjust arm mass by the counterweight.

2) By having the counterweight further out, it reduces the frequency at which the rear arm stub and weight resonates. By using a heaver counterweight, that keeps the stub resonance frequency higher, and generally of lower amplitude and so less audible

3) The arm looks rather better with a heavier counterweight closer to the pivot than a small counterweight hanging out a long way.  There may be more than just cosmetics involved, as many plinths and covers can't accommodate a counterweight a long way back.

4) In the case of a unipivot, a heavier counterweight will load the pivot more, and therefore reduce the possibility of pivot chatter. Unlikely to make a lot of difference, but with low compliance MCs or cartridges like the Decca, more weight on the pivot is no bad thing. It will increase the pivot friction, but if this is low to begin with, and increase is unlikely to be a problem.

5) With heavier cartridges, the standard counterweight can't balance the cartridge at all, even at maximum extension, so a heavier counterweight is the only sensible possibility. 

So overall, there are benefits to heavier counterweights.

S. 

 
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danilo

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Dunno.. Seems to me that Mass is Mass  :)  

Cart suspension/stylus will experience a larger mass/inertia with a 'heavier'... weight.  Regardless of the balance point.

Whether that 's Good or not, is for your ears to decide.  But I wouldn't be increasing mass.. merely on speculation.

 

SergeAuckland

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Dunno.. Seems to me that Mass is Mass  :)  

Cart suspension/stylus will experience a larger mass/inertia with a 'heavier'... weight.  Regardless of the balance point.

Whether that 's Good or not, is for your ears to decide.  But I wouldn't be increasing mass.. merely on speculation.
Yes because we're talking effective mass, inertia. Every couple has its moment.....

S.

 
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Colinjg

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Hi Serge,

Thank you for your almost instant reply.

I would agree absolutely with all of your points  except point 1 which I don't think quite answers my dilemma. 

The analogy in my head is this:

I am on a Seesaw at the park. (it only moves in one plane, but I think the concept still stands) I sit at one end with a blindfold on. I have two friends one heavier than the other, they take it in turns to have a go with me each finding their balance point.  I do not think that there is any way I could tell which one was which; my end of the seesaw will behave the same.    Even if you gave me a bit of down force. Each of them found the point where my end weighs lets say a stone and I pushed myself up and down with my legs, I still don't think there is any way I would know which of my friends was on the other end.  The mass my side of the pivot is constant and the mass the other side of the pivot changes, but the effective mass seen by me is the same in each case. ( I think.)

I think changing the mass on my side of the pivot is not really what I was getting at.  I add mass to my head shell and the stylus definitely can see that, as it sounds different( better in my case). 

What do you think?  

My head hurts!!

regards, C.

 

SergeAuckland

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Hi Serge,

Thank you for your almost instant reply.

I would agree absolutely with all of your points  except point 1 which I don't think quite answers my dilemma. 

The analogy in my head is this:

I am on a Seesaw at the park. (it only moves in one plane, but I think the concept still stands) I sit at one end with a blindfold on. I have two friends one heavier than the other, they take it in turns to have a go with me each finding their balance point.  I do not think that there is any way I could tell which one was which; my end of the seesaw will behave the same.    Even if you gave me a bit of down force. Each of them found the point where my end weighs lets say a stone and I pushed myself up and down with my legs, I still don't think there is any way I would know which of my friends was on the other end.  The mass my side of the pivot is constant and the mass the other side of the pivot changes, but the effective mass seen by me is the same in each case. ( I think.)

I think changing the mass on my side of the pivot is not really what I was getting at.  I add mass to my head shell and the stylus definitely can see that, as it sounds different( better in my case). 

What do you think?  

My head hurts!!

regards, C.
Your analysis is sound except that your friends on the seesaw don't vibrate at audio frequencies, nor do you at the other end have a clearly defined compliance. If you and they did, then the resonances on the seesaw beam would be transmitted to your compliance (your bottom!) and you would sense different frequencies depending on how far along the beam they were and therefore how much mass they were reflecting.

At audio frequencies a pickup arm is pretty floppy, not at all rigid, so the performance the cartridge sees is dependent on arm  resonances and those in turn are dependent on compliance and mass. 

The person on here who REALLY knows about this stuff is Frank (F1Eng), he used to work for Garrard in his younger days, later being Chief Engineer of a F1 team (Williams, I think), so he's probably forgotten more about mechanical resonaces than I've ever known. 

S

 
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Colinjg

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Many thanks, that is interesting. I was interested in why there would be an improvement.

Cheers,  C.

 

Bolosun

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I was with you (and still am up to a point on the why) on how a heavier/better arm weight could improve the sound. But I have changed the one on my RB303 mainly because I am using a heavier cartridge which meant the standard weight was at its limit. Also, reading all of the arm mod sites and all of saying you get the most improvement in sound with changing the weight opposed to changing the internal wiring.

So changed the weight for a GrooveTracer and there is a noticeable improvement in sound. Everything about the sound has improved, bass, treble, clarity etc. Still don't get the why, but it works. 9_9

 

f1eng

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It is not necessarily better, it depends on the cartridge you are using.

Thinking of the arm as a see-saw is only informative for setup. For use we are interested in the performance of the combination as a seismic transducer. In fact as a transducer it is only working accurately from about 2x the natural frequency of the cartidge compliance/effective mass. Lower than this the output is inaccurate. How inaccurate and by how much depends on the cartridge damping, but more damping, whilst it reduces the error around resonance, both raises the frequency beyond which the transducer starts to become accurate (to above ~ 2x Fn) and also acts as a shunt across the system at higher frequencies reducing accuracy there.

So if you want accuracy from 20Hz you need to have a Fn of 10Hz or so. A bit higher is often recommended as safer from warps but the bass is then less accurate into the traditionally considered audible region (exagerated which most people actually seem to prefer :))

There shouldn't be anything at these frequencies recorded onto the LP but warps can kick off resonance which, combined with the massive low frequency gain of phono stages, results in some pretty hideous overload of everything. Since this isn't directly audible it just causes damage so in 1976 iirc there was an additional spec added to the RIAA curve standard to add roll off from 20Hz. Very sensible but whilst it will reduce the likelihood of clipping in the phono stage and power amp on warped records the cartridge is still swinging way out of its (fairly) linear range.

So getting the equivalent mass right for the cartridge is important but whether a heavier counterweight will achieve this depends of the actual components being bolted together.

 
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Colinjg

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Thanks everybody, much appreciated replies.

I was curious as to whether there are real benefits to this or whether it was Turntable vanity, or the type of upgrade I do my system every Friday evening by drinking a few glasses of wine. ( LOL).

Clearly there are, and people are hearing benefits that my basic 1970s school Physics does not cover. There are heavier weights available for my arm, (Naim Aro) so I was curious.

Complete aside, quick question for f1eng: Why are shark fins back on F1 cars, I don't think  they look great.

Cheers Colin.

 

f1eng

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Complete aside, quick question for f1eng: Why are shark fins back on F1 cars, I don't think  they look great.

Cheers Colin.
It is just that the new rules allow it again or maybe impose it for sponsor area, I haven't checked but it is one of the bodywork rule changes for 2017.

 

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