general tonearm design question

Many popular tonearms are designed with with the fulcrum for the vertical axis at ~70 degrees (e.g. Rega, SME), rather than perpendicular (e.g Origin Live).

Doesn't the former design cause the needle to track to the outer groove as the counter weight swings downward?

...or does the cartidge/tube somehow counter this?

Would a counter weight mounted at 90 degrees to the fulcrum, yet the arm tube set at 70 degrees be the solution to this, or am I wrong?

(The reason I started wondering about this was due to the varous Rega counter-weight mods. I would think that a lower center of gravity would exacerbate this problem. Furthermore, wouldn't a lower center of gravity only be effective on a uni-pivot design?)

your thoughts?
The lower (than the vertical bearing) CG gives an arm more stability when tracking warped records. The angle of the vertical bearing is not necessarily 70 degrees but is set to match the headshell's angle to the armwand. This insures that when the arm (actually the stylus/cartridge) move up and down when (again) tracking warped records, that the azimuth of the stulus remains vertical to the record. If the bearing were perpendicular to the arm and the headshell angled, then (looking at the stylus head-on) the stylus would describe an arc as it rose up. (Was that as clear as mud?! ;--)
Nsgarch is correct on all counts (except the mud). Here's an example I often use which seems to help people visualize the stylus azimuth conditions he described.

Sit in a desk chair or rocking chair that can tilt fore and aft. Face directly forward. Extend one leg out in front so your lower leg descends to the floor at an acute angle, with your heel resting on the floor.

Holding your leg in that position, rock the chair back and forth while watching the arc described by your heel. If you're facing directly forward (perpendicular to the chair's axis of rotation) the heel moves straight vertically up into the air and back down.

Your heel is the stylus, your lower leg is the cantilever, the chair is the tonearm. When the tonearm's axis of vertical rotation is perpendicular to the cantilever, vertical arm rotations (as over warps) do not change the azimuth of the stylus.

Now scootch yourself around so you're sitting at a 20-25 degree angle to the chair. Extend your leg again and rock the chair as before. Observe the change in angle between your heel (stylus) and the ground (record). The sides of your "stylus" no longer remain vertical.

When the arm's axis of rotation is not perpendicular to the cantilever, the stylus moves through an arc and its azimuth changes relative to the record. This is the case on all tonearms with offset headshells whose vertical bearings are not offset at the same angle.

When azimuth alters with every change between record surface height and arm height (as over warps or with different VTA settings) the results will include variable crosstalk, muddy imaging and potentially uneven record and stylus wear.

Why build an arm with the vertical bearing axis perpendicular to the armtube rather than the cantilever? Because it's cheaper to design and machine at right angles. The design is inherently flawed, but when building to a price point manufacturers must make compromises. This is one they sometimes choose.
Both responses are superb,but I feel a sense of obligation to like Doug's better! -:)
Nsgarch and Dougdeacon both give great answers here, and I agree that having the vertical bearing axis perpendicular to the armtube rather than the cantilever is a flawed design.

Here's the part I don't understand. Go to Origin Live's Web site here:

and scroll down a bit. There's a top view view of all the OL tonearms. Except for the least expensive model (an unmodified Rega RB250) all of their arms have the vertical bearing axis perpendicular to the armtube, not the cantilever. Their most expensive arm is something like $5-6K, so building at right angles shouldn't be needed for hitting the price point. I'm guessing they think the design affords some advantage, but I can't see what that might be. I'm puzzled.

I saw the same thing on the Origin Live website. As a matter of fact, I have an OL Silver tonearm on my Basis 1400. I could see no change in cantilever/sylus azimuth position when I used a mirror on a few different positions on the platter.
Origin Live must know something about Tonearm design.
David, I can't explain OL's design, it doesn't make sense to me. Maybe Doug has some thoughts. . . . . .

I mean one can always make excuses like: if a record is sooo warped that if the height variation (from flat) would significantly throw the azimuth off, you couldn't play the record anyway, etc., etc. But I put my trust in the wisdom of the designers like SME and others. I'm not really sure what happens to unipivot arms when the stylus hits a bump. Anyone?
The OL design doesn't make sense to me either. I owned a Silver. It was an excellent arm for the money, really excellent, but it didn't match top level arms for clarity and resolution.

Personally I wouldn't spend $5K (or even $2K) for an arm with this flaw, since the sonic effects are of a type we're sensitive to. It's possible *some* rock listeners wouldn't care, since there are many rock LP's which cannot support too much clarity and resolution. With classical, OTOH, the more resolution the better. I just remounted my UNIverse last night after checking out a friend's cartridge in our system. The tiniest azimuth change I can manage on the TriPlanar's really excellent adjustor is instantly audible. Knowing what's possible, we wouldn't be happy settling for less.

I'm not really sure what happens to unipivot arms when the stylus hits a bump. Anyone?
Most unipivots, it seems to me, rely heavily on stylus/groovewall pressure to help stabilize the arm in the azimuth plane. After all, they're quite "floppy" until the stylus hits the groove.

This has always seemed like a serious design flaw to me. Our poor stylus, cantilever and suspension have plenty to do following groove modulations without having to help stabilize a structure that outmasses them by 100x or more. (Paul and I both think this is a major reason we dislike a certain arm that I won't offend SS by naming. Let's not go there again!)

Someone once tried to convince me that the azimuth rocking of an unstabilized unipivot keeps the stylus in perfect azimuth relative to the changing groove angle on warped LP's. That's nonsense of course. It would be true only if the stylus were capable of rocking the arm to match the groove angle with ZERO time lag and ZERO overshoot, which is patently impossible. The mass of the arm and the compliance of the suspension will always create a delay between the input of uneven groovewall pressures and the readjustment of the arm angle. By the time the arm reacts the warp would have changed the groove angle, you're always behind, and then the arm would overshoot. Adding outrigger weights would not necessarily help, and it could easily make matters worse depending on warp angle, warp frequency, cartridge compliance and the rotational inertia of the arm. That's too many uncontrollable variables. Stability may be a compromise, but it's the best sounding compromise to our ears.

The Basis Vector and Graham Phantom are exceptions among unipivots of course. Each stabilizes itself, in its own way, leaving the stylus/cantilever/suspension to do their primary job. I think this is a major contributor to their increased clarity vs. their unstabilized cousins. The Phantom's non-contact method of stabilization seems especially ingenious, since it preserves the design advantages of a unipivot while eliminating the disadvantages. Kudo's to Mr. Graham on that one.

Don't worry,Doug.No problemo.Feel free to mention the 2.2,it really would be silly for me,or anyone to get offended by a product comment.So long as the product sounds good,I don't care.The past is an embarrassment to me,so don't sweat whatever you feel like saying,at any time!!
My friend just got the Phantom,and it is superb.Being that we both have "flat platters",at all times,due to vacuum,the issue of the "true" unipivot 2.2 does not seem to be a big deal to me.I never see any twisting movement of sideweights when playing LP's.Yet,I think the Phantom is fabulous.It has it's own idiosyncrocies though!
BTW,yes,the Triplanar is not so bad either.-:)
Doug. Are you saying the azimuth on a uni changes each time you adjust the VTA? WouldnÂ’t a unipivot simply keep a consistent azimuth over an elevation on the record? I cannot recollect that I have ever had to adjust azimuth after I adjusted the VTA on any of my unipivots, and I frequently play with VTA adjustments (almost on every record).

Doug. Are you saying the azimuth on a uni changes each time you adjust the VTA?
No Pauly, I didn't mean to imply that at all. Sorry if it came through that way.

I was suggesting that IF an unstabilized unipivot relies on stylus/groovewall and cantilever/suspension pressures to help maintain steady azimuth, then:

a) this could make it more difficult for the stylus/cantilever to respond freely to subtle groove modulations and;

b) this would tend to make for constantly changing azimuth on WARPED records. If azimuth depends on the angle of the groove walls, and if that angle changes due to a warp, then... obvious conclusion.

Point (b) is virtually insignificant IMO. An arm with fixed bearings will maintain stable azimuth relative to the platter, but if the record is warped the azimuth relationship of stylus to groove will change because the groove is changing. I only mentioned it to counter the (silly) argument that someone once offered that a unipivot could compensate for warps by changing azimuth in real time.

Of course we should all have SirSpeedy's vacuum platter. Then point (b) would be non-existent!
Doug,I honestly don't know of "any" unipivot that relies on stylus/groovewall and cantilever/suspension pressure to help maintain steady azimuth,or balancing.That,alone,would be poor design,and would surely put a "TON" of pressure on the stylus/suspension.Who knows?Maybe I have more to learn,but I don't think my arm,or my friend's VPI rely on this.
They sure sound good though! -:)
BTW,without you knowing it,I am reporting that your EP-15a listing(Nsgarsh too) aided me in getting one!I included the Exact Power Ultra-Pure to go fully balanced.THIS combo is the the biggest improvement I have made to my system in a long while!Stuff like vta/azimuth/downforce changes are WAY more obvious with super clean A/C,and I'll bet many folks don't know how much more can be had!
Best regards!

Glad to hear you're enjoying the EP units. Have you tried the EP-15a without the Ultra-Pure? I'd be curious to know how much additional benefit you hear from the balanced power.

BTW, upgrading the power cord from wall to EP-15 also makes a significant improvement. So does putting it on Rollerblocks. Strongly recommend you try both if you haven't.

Meanwhile, about the "Wobbly" Theorem:
I honestly don't know of "any" unipivot that relies on stylus/groovewall and cantilever/suspension pressure to help maintain steady azimuth,or balancing.That,alone,would be poor design,...
Well, I'm glad you said it first! ;-) But if there wasn't a problem (aka, opportunity for improvement), why did AJ Conti and Bob Graham go to such trouble and expense to give the Vector and Phantom additional stability? You've heard the benefits on the Phantom yourself: clearer, more resolving, less muddy, etc.

...and would surely put a "TON" of pressure on the stylus/suspension
Well, not quite that much. ;-) With a vacuum platter holding the record surface flat, the only impetus for an arm to roll comes from groove transients, which are pretty small events. The pressures being resisted are only significant to a mechanism as tiny and delicate as a phono cartridge. It might not matter to a low resolution cartridge, but to an Orpheus, UNIverse, XV-1S, etc., everything matters.

Who knows?
I admit my little theory is just a hypothesis. But consider the available evidence:
- a unipivot wobbles freely until the stylus touches down
- once the stylus is under full VTF, the arm becomes more stable
- nothing in the tonearm has changed to provide this stability
What other mechanism can we posit for the system's sudden increase in stability than assistance from stylus/groovewall and cantilever/suspension pressures? What else has changed?

Let's do what real scientists do with a hypothesis. Devise a test to prove/disprove it. (I'd do it but I don't have a unipivot lying about, so you're nominated if you're willing.)

1) With the armtube on the cueing support, nudge the finger lift upward with a given amount of force. "Measure" the arm's freedom to wobble by visually noting the amplitude of angular deflection and the length of time/number of cycles it takes to return to stability. Repeat a few times until you're confident you're applying the nudge consistently.

2) Cue the stylus down onto a blank (ungrooved) section of a non-spinning LP. Repeat the nudge test using the same upward force. Note the results.

3) Cue the stylus down into a groove on a non-spinning LP. Repeat as above.

Let us know how the arm's freedom to wobble in response to a given impetus changes under each condition. If my hypothesis has merit, the freedom to wobble will be greatest when the stylus is off the record, less when on the record and least when in a groove.

You could test unipivots for azimuth stability by throwing on (just said that to make Doug cringe ;--) an SQ Quadraphonic record. Its groove not only deflects the stylus left-right-up-down, it TWISTS it CW and CCW!
Hah! Great idea! Mozart wrote a piece called 'Notturno for 4 orchestras'. I have a London blueback copy in stereo, but I'm sure it would sound more like what he had in mind in quad. Surround sound ain't exactly new! ;-)
Doug,truthfully I don't hear anything in my friend's Phantom/Orpheus combo to make me want to change arms!Of course we have not done a side by side comparison,but I installed the Orpheus in his 2.2,and a dealer did it when the Phantom came( I know his system like my own).I,then,re-checked and voiced it to a more acceptable(to our circle of guys)level of performance.The Phantom is superb,but you are WAY underselling the 2.2!Old story,but NO problemo!!-:)
The Orpheus IS another story!I definitely like it WAY better than the Temper-v,which he had(I still do,but need more hours to justify a change).
Mind you,I really don't have much enthusiasm for the hyper technical(though I have NO reason to doubt your theories,which are usually well thought out,btw)comparisons,to prove something on paper.This does NOT mean you are not absolutely correct,but my 2.2(especially after the NEW Power Management System)is "really" giving me incredible performance!Could care less about the magnaglide as my arm NEVER tilts/rocks during play(really).I sense just a bit more air in the 2.2,with more weight in the Phantom(sort of like the superb SME-V,here).

I DO know what my Mercs,Lyritas,Deccas etc should sound like,and believe me if a unipivot sounded anything less than superb my friend Sid Marks,the LP maven(in spades) would never have sold his Air Tangent,and replaced it with a Unipivot design.Though I definitely liked the AT better.If there was a problem in my tracking,he would "destroy" me,and it is his dogged critical nature that has rubbed off on me,and gotten me in trouble on this site.Yet you are being a bit too picky,and trust me,I know not to tread too heavily with you,here!The performances,with all the other variables in place are really NOT all that big.
For that matter,the argument made by the reviewer,talking up this new arm called the SEPTUM(see the TNT website)has as much credibility,for "low parts count" as your argument against unipivots.He writes a very engaging design description,that makes alot of sense to me,but I am getting way to long in the tooth to argue anymore.My 2.2 is admittedly VERY finicky to set-up(that fluid again).Way more-so than the Phantom,which is less critical to fluid,but I like the latitude available(at least to me)with the 2.2's flexing of parameters.That is JUST me.Meaningless to anyone else!
I do have superb aftermarket cords on the EP stuff.The 15a came after the balanced Ultrapure,but it greatly enhanced the Ultra's performance.I am a big believer in fully balanced,so I never went the other way.INCREDIBLE combination!!!!!
Well,thanks for the communication,and best to you.