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Strange Tonearm Tweak. Long

As you all know, I am a little different. I like to read and study stuff like tonearm technology. I noticed that some of the better unipivot designs have employed "outrigger" style outboard weighting systems on their arms, that work like a tightrope-walker's balance pole. This not only balances azimuth, but also gives the arm better stability to lateral deflections from the cartridge suspension, so the arm is not moved when the stylus is pushed laterally by the groove information. I began to think on this, and I wondered why no gimbal-bearing arm makers are doing this. Surely since the vertical plane rides on a vertical axis bearing, there is still some chance for the arm to be laterally deflected by the stylus, when the stylus should be doing all of the moving, not the arm. I think that this is why they use heavy arms, but a heavy arm in the vertical movement plane is not good for tracking. A heavy arm in the horizontal movement plane is good for resisting sideways deflection that would impair pickup function.

So I decided to try increasing the mass of my tonearm in the lateral plane, while keeping it light in the vertical plane, by the use of "outrigger" weights, just like a unipivot does.

I bought lead fishing weights that looked like long rifle bullets(just the lead part) They were about an inch long and about 3/8" diameter, and weighed 12 grams each. I drilled into the bases about 1/4" and press-fitted them onto the nuts that hold the arm into the bearing yoke, so they stuck out straight sideways, like sideways spikes. This put the weight out pretty far to the sides as outriggers, and kept the weight centered exactly around the bearing pivot axis so it did not increase the vertical mass significantly, but it did very slightly. It did not influence the tracking force at all.

So now the arm had outrigger stabilizers on it in the horizontal plane of motion.

I put on a record and sat down to listen. Let me tell you, fellas, this was a mind blower. I have never heard this much information come out of a cartridge before. I heard sounds on records that I had listened to for 30 years, and never knew those sounds were on the record! And I have had some pretty good analog gear in my time. And what I didn't own, I heard at the audio store I worked at. This is the most astounding mod I have ever heard on a tonearm. And it cost me $1.49 for the fishing weights, and I got 3 extras.

The only slightly negative thing about it, is that it increases the anti-skating force, so you have to cut that back a little, and if you have some marginal scratches that might skip, they are more likely to skip with this mod, due to the resistance to sideways movement provided by the outriggers. I had this happen once last night, but I didn't consider it a problem.

But the increase in dynamics, and detail and overall sound quality is astronomical. It blew me away.

I have a DL103, which is a very stiff cartridge, and it may be that this is not needed for a higher compliance cart. But, I think that it would be good for anything that is medium or lower in compliance.

The key to it, is that it only increases the resistance to sideways movement, without interfering with the effective mass of the arm, or the vertical swing movement that needs to stay light to track warps. I played some warped records with this mod, and they played just as well as without the mod, except they sounded better.

I have a pretty good analog setup now, but I can say without reservation, that this mod made my rig sound better than any analog rig that I have ever heard in my life. I have never heard a Rockport.

Stabilizing the arm against unwanted lateral deflection increases the information retrieval and dynamics by a very large percentage. If your arm is not set up like a Rega style arm, then you can glue a 1 ounce long rod across the top of the bearing housing(sideways) like a tightrope-walker's balance pole. Use lead if you can, it won't ring. You don't have to do any permanent changes to your arm that might wreck its resale value to try this out. If it has anywhere near the effect on your system as it had on mine, you won't be taking it off.

It may come close to the movement of your cueing lever, so make sure you have clearance to use it. Mine was close, and I have to come in from the side now to use the lever, at the end of a record. That is fine with me! This was a major, major improvement in the sound of my rig. It is staying permanently. As in "forever".

If you are a little tweak-oriented, and not afraid to do stuff like this. You should try it. It will knock you over.
twl
zaikesman
3,017 posts
 
I want to go just a bit further and break down just why I feel Tom's idea constitutes a intriguing and enlightening approach. In the past, before coming to some understanding (with the help of the contributors to this thread) of what the HiFi mod represents, I had - I'll assume like most of you - regarded effective mass as a monolithic quantity. Tom's insight made me aware that we should properly take into account two separate quantities of mass, vertical and lateral.

The reports above of those who've tried his mod testifies to the validity of his fundamental underlying proposition: that information retrival may benefit if these two quantities are not treated as being always interchangable - that in fact, performance may be improved if these two quantities are made slightly divergent. Two divergent effective masses instead of one also implies there being two divergent points of resonance (cartridge compliance still assumed to be constant in all directions). I wonder if this presumably 'double-humped' resonance distribution might itself be partly to credit for perceived performance gains, as a result of the altering of the system's "Q" characteristic to be less intensly concentrated at one specific frequency ; in other words, maybe simply making the lateral and vertical mass - and therefore resonance - components somewhat different from each other could be as significant a reason for improvement as the action of additional lateral mass itself.

This an untested hypothetical of course, but we do know that there is a several-Hertz range within which 'proper' system resonance may ideally fall, usually given as from 8 to 12 cycles per second. This value range is considered low enough not to be excited by music, but high enough not to be unduly excited by record warps, big dogs, passing 18-wheelers, distant earthquakes, etc. So there is obviously 'wiggle room' to for instance make the vertical-mass/cartridge-compliance resonance point = 10Hz while the (higher) horizontal-mass/(constant) cartridge-compliance resonance point may be brought closer to say 5Hz without having to worry about extraneous inputs of (primarily vertical) infrasonic energy ruining your tracking day.

The viscous fluid approach , while not imparting inertial effects (and in fact counteracting them), does little to damp such low frequencies, and won't really alter the distribution of the system resonance. (I want to stress here, in relation to this inertia business, that Tom's added weights do not encumber the cartridge suspension in a discriminatory manner that is out of the ordinary ; the suspension must deal with the tonearm's mass inertia anyway, whatever its value. Gravity helps maintain groove contact in the vertical dimension through the VTF setting ; laterally - particularly with really good bearings - it seems to me that inertial mass ought to be able to stand an increase at least roughly equivalent to the VTF.) I observed near the top that fluid damping ought to be superior to the HiFi implementation in terms of HF damping, and this analysis suggests that maybe the two concepts are actually complimentary.

Funnily enough, after so long since this thread began (and after having previously inspected my own tonearm to see if it could be made to accept something like Tom's mod, which I concluded it really couldn't due to its physical design), this late conversation spurred me to go downstairs and look once again - this time with a new notion in mind. And hot damn, there it was: the 1200 tonearm already incorporates added mass in the lateral plane! I'd been looking at it the whole time (the brain sure can work slowly... :-) I think a lot of gimbal tonearms have been made like this: it has a 'carriage' containing the vertical-plane bearings which itself rotates in the horizontal plane (it's mounted within the 'tower' assembly holding the horizontal-plane bearings, which is itself stationary). This 'carriage' structure is basically a rectangle, open in the middle (the arm passes through it), made of cast alloy about 1 1/2" wide by 3/4" tall by 1/4" thick, which incorporates the steel vertical bearings ; when the tonearm moves vertically it remains put, but it rotates in the horizontal plane right along with the tonearm when it is moved laterally. I would estimate its total mass as being roughly in the ballpark of Tom's fishing weights. D'oh!
twl OP
3,251 posts
 
Good points, Alex. In fact, some tonearms do have added mass in the horizontal plane, provided by the bearing housing structure. Others have a large bearing housing, but the bearings that control horizontal movement are only holding a low-mass ring which is part of the gimbal system, so those don't really help in that regard.

In early tests of the other OL arms like the Encounter and the Illustrious, I found that the horizontal mass(large bearing housing) in those arms was already sufficient to preclude the use of the HiFi mod. And in fact, they sounded better than my OL Silver with the HiFi mod. This shows that horizontal mass is important, but is only one aspect of the design, and other things still are very important.

Your comments about the amount of mass increase being similar to VTF force is very astute. However, the mass increase that I use is about 12g per side, or a total of 24g. This is placed at the pivot, which is not augmented by the F x D^2 multiplier of the long arm tube that multiplies the effect of stylus accelerations at the pivot. In order to counteract forces and accelerations that are multiplied by the leverage of the long armtube(9"), a larger mass is needed at the pivot, than the typical cantilever and suspension may be exerting at the headshell. Even this 24g increase seems insufficient. My testing has shown that even though the increased mass may seem insufficient to counter the forces and accellerations that the cartridge produces, it is the increase in Coulomb's Friction(static inertia) which is the key to this HiFi mod's performance. This increase in Coulomb's Friction causes the static moment of inertia of the tonearm system to be higher than the stylus deflections can overcome on a short rapid momentary acceleration during play. This is why the cartridge performance is increased, but the slower movements of spiral tracking of the groove are relatively unaffected. Higher amounts of mass increase could be counterproductive to normal arm movement across the record. I know we had this discussion about static moment of inertia earlier in this thread, but I neglected to mention Coulomb's Friction at that time. It is different than the typical dynamic friction that we are all familiar with.

Doug Deacon's HFNRR test record measurements with the Hifi mod installed on his OL Silver yielded a near perfect 11Hz vertical, and slightly higher horizontal with a Shelter 501 Mk II on his arm (if I remember his post correctly) Both were well below normal audio range, and above rumble frequencies.

Regarding your interest in higher frequency performance of the damping trough, it is interesting to note that studies have been done on arms with removeable headshells, and it was found that 1kHz was a typical resonance peak resulting from the joint of arm/headshell. If the damping trough works well at that frequency, it may well prove very effective on that resonance, as well as others.

A damping trough working in conjunction with increased horizontal mass is an intriguing idea which could merit some experimentation. I have not tried that combo personally. It sounds like a good idea.

Thanks for your input.
dougdeacon
3,338 posts
 
"Doug Deacon's HFNRR test record measurements with the Hifi mod installed on his OL Silver yielded a near perfect 11Hz vertical, and slightly higher horizontal with a Shelter 501 Mk II on his arm (if I remember his post correctly) Both were well below normal audio range, and above rumble frequencies."

From memory:
OL Silver
HIFI Mod
Tom's suspended counterweight (described above, I think)
Shelter 901
~ 9Hz horizontal
~ 11-12Hz vertical

The suspended C/W is not quite as heavy or as close to the pivot as Tom intended. OTOH, reducing the vertical moving mass would raise the vertical resonance frequency still higher, right?

If Alex's new thoughts are correct, then it's okay or even desirable to have the lateral resonance freq lower, and reducing it even more might have a good effect. I'll have to add some bubble gum to the weights, remeasure and do some listening. Any suggestions for the best flavor? ;-)

Doug
twl OP
3,251 posts
 
Doug, thanks for clearing that up. I couldn't remember exactly what you stated in your post, and I just made a mistake in writing that you had a 501.

BTW, I have always thought that Bazooka was the best bubble gum! :^)
zaikesman
3,017 posts
 
Double Bubble. It reinforces the effect of the divergent resonance points... :-)

Tom, your technical analysis of what might constitute the optimum range of added lateral mass and why is a good deal more sophisticated than I could manage (not that I can't follow the gist of it, i.e., what matters are the forces in play at the stylus tip with mechanical multipliers taken into account, not the raw masses involved - I think). So I will just second it with an alternative observation: the existing counterweight on any conventional tonearm is at least as massive as your 24g of added weights, and I would guess probably more often 2 to 4 times that amount, whereas the cartridge, out at the end of the tonearm lever, is roughly 1/2 to 1/4 as massive (as the added weights). At set-up, the counterweight is first balanced against gravity with the cartridge installed, then moved inward toward the pivot to effect the desired vertical tracking force. This action could be seen as 'unbalancing' the cartridge in the lateral plane by the same amount as the applied VTF - and Tom's added weights could be seen as a method of 'restoring' static lateral balance by providing a 'counter-counterweight' that operates only in the lateral plane.

Of course that's not a literally true analogy, because gravity is operating only in the vertical plane, but the lateral accelerations applied by the spinning record at the stylus tip are real, and they can be presumed to be basically equivalent to the vertical accelerations (caused by same) that gravity is enlisted to help manage in the vertical plane. Now, because the groove wall is cut in a 45-degree "V" angle, the downward VTF applies the same restorative force in the lateral plane as in the vertical when the stylus is deflected side-to-side. There is a difference however: in practice, the cantilever is always deflected vertically upward by the VTF, even at rest, whereas laterally it always returns to center. Given that scenario, plus the fact that warps which need to be tracked by the tonearm are mostly a vertical phenomenon, there would seem to be elbow room so to speak for increasing what we might call the 'lateral dynamic tracking force' against which groove accelerations act in the lateral plane. In other words, we can think of Tom's approach (of increasing lateral mass) as effecting a sort of separate, and higher, "VTF" for the lateral plane.

These musings inspire a vision of what Basement refers to as a 'properly designed' (pivoted) tonearm: maybe such a creature would have not just a rear counterweight, adjustable forward and backward to effect proper tracking force, but also side counterweights concentric with the pivot point mounted on extensions of the fixed axle, adjustable in and out from the pivot in order to effect optimal lateral counteractance to forces applied at the stylus - while the whole shebang would be fluid-damped. (And: might such adjustable side-weights even be able to effect some form of dynamic anti-skating compensation?) This seems to me the logical extrapolation of Tom's mod...
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