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In Reply to: Rega counter weights (again?!) posted by Aleksunder on September 11, 2006 at 06:07:53:
***The problem is that they also dynamically vary VTF with pitch (vertical movement) of a tonearm (a Bad Thing), and possibly also add a resonance in this mode. Unipvots are almost always damped, which presumably helps to negate this.***The offset counterweight actually places the median mass of the counterweight in the same plane as the stylus. This improves every aspect of tracing. PERIOD---No ifs ands or buts.
All of the higher end Rega arms incorporate an offset counterweight, and most aftermarket Rega mod arms incorporate an offset counterweight.
There is absolutely NO tradeoff. The stock counterweight is a sonic disaster IMNSHO.
I have not tried O Malley's mod. I am interested to see if it impacts the sound in any way good or bad.
As for Unipivots always using an offset counterweight, this is because with a single pivot point the tonearm must be precisely balanced in all planes for it to function at all. Again this is confirmation that offsetting counterweights is the correct implementation of that aspect of our hobby.
Follow Ups:
... what happens with a suspended/pivoted/'smart' underslung C/W?
..the vertical pivot of the Rega is in the centre of the 'beam' formed by the arm tube, i.e. above the plane of the disc.SME use a pivot which is dropped to the plane of the disc surface specifcally to allow the use of an underslung C/W, and this is 'correct' geometry.
The stylus transcibing the groove has a mass, it also has a vtf. You want the counterweight's median mass to be at the plane of the diamond if you want to provide the least amount of vtf variation as the diamond moves vertically.Sorry if I sound know it all about this but I am designing my own tonearm right now and the cgi 3d 128 bit evaluations show any other counterweight option to be poor option.
Again it is the median mass of the counterweight that needs to be at the stylus plane. How you hang it there is up to you. I think a slung counterweight is a great option on many tonearms since you can create more median mass with a flat plate than a round offset counterweight.
I am sure Mark Kelly can give you the math on this since he is building a tonearm as well.
"You want the counterweight's median mass to be at the plane of the diamond if you want to provide the least amount of vtf variation as the diamond moves vertically."
======================================================
Actually, what you REALLY want is the line formed by the arms's CG and the counterweight's CG to be perfectly horizontal to the record when the stylus is resting in the groove.
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.
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.
" ... the cgi 3d 128 bit evaluations show any other counterweight option to be poor option ... "Tell us more about this method of designing a tonearm.
By the way the software support for this software costs 55,000 per year to the company that owns it.The software is identical to what they used in Hollywood to create the movie Twister. I have a friend that models vehicle designs and drives them for say a million miles before they ever go to prototype.
He is doing this as a favor if I build him a Maple plinth like my last project. The earlier assumptions I had made regarding the design and execution of a counterweight all failed modeling. I am trying hard to get this down, but if it is successful I will want to apply for a patent for both the product and for the manufacturing processes to create it. So greater details are not likely to be presented here--nor pictures of any type.
I seriously doubt China will honor the patent.
Though I suppose the Chinese won't respect that either. Damn them!
He said the air polution from their industrial engine has choked out the sun. Even in mid day they cannot see the actual sun. I remember reading in text books about London back in the industrial revolution with the same type of comments....Makes you think the Kioto agreement should be renamed the Bejing clean up.
Well here I am sitting in front of two big monitors with that very software open doing special effects for Hollywood films, which happens to be my job.
Anyone else care to swap a fine plinth for my Garrard 401 for a 3d cg model of a tonearm?
They are similar and different. I doubt Maya runs 128 bits! I think it is a 64 bit software.
Alias is a software company, bought by Autodesk not long ago. Looking through their products I guess you mean the one they've renamed AliasStudio. Autodesk have been putting their stamp on everything since they bought the show. No, I can't say I know that, I use Maya which used to be Alias Wavefront.
Yes and when I took my Son to see the USC film school they were proud to display a dozen 64 bit CGI computers with Maya. Cool stuff if you want to do computer animation and games.Alias was big time stuff and I wonder when they were bought by Autodesk which is itself a great company as well.\
I have a copy of Autodesks universal readers around my computer within say 8 feet! We used it extensively to view any image file ever imaginable for document management purposes.
You are One Patently Preposterous Pup, tubes.
And actually completed it within some sort of realistic deadline....Patents take time and I want to test the real deal extensively before I spend the bucks. This is expensive on my kind of budget.
Tubes forever (w/ Super X-Ray Monocle Of Doom) with trusted advisory staff and CAD-assisted Patent specialists......
I have friends because I am nice. I ask a million questions. I try to learn from people who know more than myself. And I NEVER take myself seriously....EVER. My friends love that I am regular people material.So have you finished that Garrard plinth of yours or are you on year four?
You should have a patent on busting my ass! ;-) I am beginning to enjoy it!
Just to re-trace a well-trodden path -- when someone whose output here consists of deeply mistaken assumptions resting on imaginary expertise --- tells you they're working up a Patent design --- it really tears at the old fabric of credibility, doesn't it ?Since, as you have mentioned it, you 'never' take yourself seriously, I would suggest the following :
In the unlikely case that a newcomer might not distinguish a Tubesforever post from a normal, reality-based post, you should just attach a tagline at the end of each one of your posts.
Something like :" No actual user serviceable expertise or information contained anywhere herein. Any resemblance to a knowledgeable opinion or actual assertion of fact is strictly coincidental and, after all, pretty unlikely in any case. "
............................ Tubesforever , CPA, CIA, PhD, Krell, Nasa, Wells-Fargo................................I think that's the only honorable solution.
J.D.
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Bust my ass, but do it with a little more dignity. Sir Winston Churchill was at a party when a women walked up and admonished him that he was drunk. He said, Madam I am drunk, but tomorrow I will be sober but you will remain ugly.Learn from a master....keep your rants short and to the point.
I off you no pictures, no descriptions, and no hints as to the design of this tonearm--which has changed a great deal over the last several months. The time with the Alias program has been illuminating.
You know I respect you JD, so tone it down a bit. Spend your time on 301 pics which we all enjoy.
I'll be happy to dose up a bit.
You lighten up a bit on the all-areas expertise effect.
And no, it's not a temporary restriction.
Doing something once --does not entitle you to dispense expert opinion on same.
Having done it more often than 'not at all' does not an expert make.JD
trhy this for inspiration ...
~Slainte,
The OMalley
A meditation on existence & tranquility.
I have access to Alias myself. Several years ago I designed a turntable and an engineer I had worked with owned an Alias "license" or seat. It is a lot more complex to model a design than you may think. All dimensions and material types have to be known. You then must create the geometry of said model, and even then, results may or may not be completely accurate, especially if you are seeking resonant frequencies and the like. A counterweight may be a simple model to create so let us know your findings.
His outfit is top flight and he does this on his time. My early work with him was to define every aspect of the material, hardness, mass, and then start work on how to keep the stylus planted into the grooves.What started me on this was reading Mosin's information on the Unitrac Magnepan arm.
Basically its designer was trying to create infinite mass at the headshell and the least possible effective mass for the tonearm. That way the cartridge sees a brick wall so only the suspension of the cantelever is doing its dance.
I would say it is extremely effective. When I first mounted the Grado on the arm I was immediately taken by how much more detail and bass I was hearing. Like focusing a lens on an SLR camera. Everything just sounded more lifelike and natural.
I just worry that Alias will point me in a direction but the sound may or may not be better. If the sound does not beat the Unitrac then I quit my tonearm project. I would rather spend time listening.
While my friends analysis is really awesome it is totally theoretical and just flat out fun. We are running an analysis of 60 hz bass gitar riffs and 350 hz female vocal belts. So far the women are harder to track.....what does that mean?
I only used the idea. TWL at Audiogon is the man.
No Rega arm uses an eccentric counterweight.The Graham is a very noteworthy unipivot which doesn not use an eccentric counterweight.
And yes, the eccentric C/W when used with a Rega arm causes a nonlinear change of the VTF.
The mass of the C/W at stylus height means nothing. The arm has fixed bearings and cannot tip sideways.
... relative to the pivot, which is located in the 'tower', well above the center of mass of the arm-tube and C/W.
it is concentric with the armwand and the bearing oint is at that same location.Do you have one? Take it apart, I have.
.
It has nothing to do with the counterweight like with the Hadcock for instance where it does double duty.
Not the plane of the bearings.
when the sylus goes up in the air the VTF changes. when the sylus dips the VTF changes. with a dropped counterwieght the theory is that the changes in VTF are beneficial in that they keep the stylus from digging in and rising off the record. Some contend otherwise.So with a dropped counterweight the beneftis you are looking for and claimning that you get come directly from, among other things, changes in VTF.
As the cartridge rises it forces agasint the intertia of the dropped counterweight which keeps it down. When the cartridge dips, the inertia of the counterweight does not let it fall 'quickly' thus, and for all time, VTF be helping. The benefits are derived from a transitory imbalance.
all this is becuase the counterweight IS dropped and that is does rise above and below that level of the sylus.
I didn't make up any of this up and it ain't original to me. It is merely how I understand things mith my tiny head.
Now, I am going down to the other end of the bar and finishing my drink.
"when the sylus goes up in the air the VTF changes. when the sylus dips the VTF changes. with a dropped counterwieght the theory is that the changes in VTF are beneficial in that they keep the stylus from digging in and rising off the record. Some contend otherwise."Exactly so. What advocates of the solid underslung weights are not taking into account that an arm tracing a disc is a 'dynamic' system, not a 'statically balanced' one.
IMO the sonic benefits of an uderslung weight are not to do with tracing (at least, in a Rega) but with with balancing/stabilizing the load on the two vertical bearings, i.e. stabilizing the whole beam assembly in the 'roll' plane (that aircraft terminology again). I believe this benefits the way the bearings transmit audio-band vibration to the pillar and hence to 'ground'.
Were thet spaced well apart in a yoke, rather than pressed into short stubs in the Rega's tube, it wouldn't be a problem.
is this what you are saying? stablility[less noise] = wide apart bearing sets.
Symmetry is important to vinyl replay I think, especially stereo.If the bearings supporting the 'beam assembly' (cart., tube, counterweight) are spaced (equally) well away from it's centre of mass, they 'take the weight' equally and will behave in a more ... linear (?) way when they inter-react with the yoke, the arm-pillar, the arm-baord or plinth, the equipment stand .......................
Tires wider apart make for more stable secure traction. The outrigged weights may compensate somewhat in this regard, sort of like the bar a tightrope walker uses.
The outrigger weights act in two ways. My guess is that they absorb the vibrations and resonances of the vertical bearings. Second they add unsprung mass to the arm itself so it increases mass without increasing effective mass of the tonearm.
They are not attached to the arm, just the bearing/yoke assembly, so they add zero mass to the arm.i can't speak to them absorbing resonance from the bearings but their purpose, mass qua mass, is to add that mass outward on a horizontal plane to create, litteraly mass/inertia to slow down the arms movement along that plane, or to stablilize the arms back and forth movement.
Why? When the cartridge is 'excited' by the groove it will over-react [think Grado here in the extreme] and cause the arm to react as well. Some think this is good in that the arm is nible and allowing the cart to 'do it's thing.' But, stopping that arm from reacting is the point. Keeping that arm stable but fluid keeps that cartridge/stylus riding smoother/deeper into the groove. The cartrdige should move and send that energy up then cantilever into the coils, etc. Hold that cart still and stopping the arms reactive movement stops feedback to the cart. NO WIGGLING. Keep that arms steady to keep the cart steady so that the sylus/cantilever can react to the grooves ONLY means ... a higher level of fidelity[truth in movement], dynamics[deeper in the groove], detail, able to calmly reproduce subtle changes in the groove.
Can you see that picture?
I would describe this modification as akin to the balance beam a tightrope walker uses. Well sort of.But locating the two largest masses, namely the cartridge and the C/W at the very extremes of the "stick" contributes to the same type of stabilization. The idea of the C/W close to the pivot is counterintuitive.
The bearings are in the armtube not the yoke so they can be adjusted more easily for preload.Just because some guy has time on his hands and has created Gandystein's Monster doesn't mean it is all sound engineering. There is alot of NIH going here and there.
.
I didn't come here for an argument, Garth, just some considered input.It should be obvious how important 'symmetrical' behaviour is in a tonearm playing a stereo source. Imaging?
I don't know why you're even taking issue with my stating that the cost-compromise design of the Rega included a far-from optimal way of pivoting the arm-tube (for all the arm's many other virtues, which make it such a playground for inventive tweakers).
Was that it offset the angle of the vertical pivot to the angle of the tonearm.Technically this is done to minimize the torsional effect of the counterforce to the stylus.
so symetry is not always the best method. Sometimes offseting angles are better....
And offset counterweights is still up in the air!
.
The spacing of the bearings is I feel irrelevant.
Movement? I said nothing about "movement". Re-read the post.The spacing of the bearings is I feel irrelevant.
The reason to move bearings outboard is because they do vibrate, and it is best to decouple the vibration from the arm wand as much as possible.The distance is not an issue. The resonance and vibration is an issue.
And dropping the mass of the counterweight below the plane of the stylus just creates the same mistracking issues as a counterweight above the plane of the stylus, just the opposite force is applied.
The best model I have seen is with the counterweights median mass at the exact plane of the stylus. BTW I love how Graham does his arm. with the opposing magnetic structure for damping and stabilization. Pure genius.
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