[*Scotty*]

Resonance in a mechanical system is fairly simple to describe if the system consists of a spring and a mass. Damping can change the Q of the resonance but not the frequency. I don't accept without reservations any of their statements regarding the claimed horizontal and vertical resonant frequencies. They don't show their calculations or how they measured the vertical or horizontal resonant behavior. All we have are claims without substantiation.
 If adding mass solves some kind of buzzing problem this suggests tracking force inaccuracies first and some kind problem with  total moving mass second. I am not saying that there may not be a problem with insufficient mass, a problem analogous to a stiffly sprung pickup truck on a wash-boarded road with no load in the bed, you have to slow down to stay on the road which is not an option when playing a record.
Scotty

[neobop]

You'll get no argument from me on that score.  Info seems deliberately vague.  Here's the discussion on Agon:
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1200430667&openfrom&10954&4#10954

"IIRC Poul Ladegaard, the inventor of the concept linear arm that spawned Trans-Fi, mathematically modeled that horizontal force operating on the cartridge cantilever on a linear arm of up to 300gm is still minute relative to a pivot arm of typical off-set and overhang. So in theory at least, there should be no damage done by experimenting with more horizontal mass.

The ability to separate the adjustment of vertical effective mass from horizontal mass has been helpful. While holding VTF constant I can hear significant changes in performance as the front and rear counterweights are spun out from the pivot point. Stubborn tracking and sibilance problems that cannot be eliminated by adjusting VTF can be resolved by varying vertical effective mass. The stock Trans-Fi short wand sounds good with all of the medium- and high- compliance cartridges I have tried. However, the variable- mass arm broadens the sonic palette of each cartridge and deals with the occasional seemingly intractable tracking problem."


"I'll run through calculations of optimal vertical mass as I mount the next few cartridges on the wand. So far I've been placing the front and rear the weights by ear. The wand can be pretty much anything from almost massless to massive-- one or two negligible 6"x 1/8" alum cantilevers(3" rear projection + 3" front projection), one or two rear counterweights @10gm, one or two or no front counterweights @5gm, and a std. headshell that plugged directly into the pivot has minimal inertial mass relative to placement at the end of a conventional pivot arm.

I've tried it with as little as 35gm horizontal mass and as much as 100gm-- approximating the range of horizontal effective mass from ET to Kuzma airline. So far less horizontal mass sounds better in all instances. This does not hold true for vertical mass.

I mounted an Audio Technica ART7 today to an Ortofon LH6000 magnesium headshell. After several hours it's clear that ART7 surpasses DLS1."


"I have a Hi-Fi News test record with horizontal and vertical resonance tracks that may be helpful moving forward. Thus far I set up by ear, running out the front and rear counterweights while holding VTF constant and adding just enough effective vertical mass to reduce audible distortions. Too much mass and sound deadens and soundstage collapses, similar to over-damping effect.

In all honesty, adding horizontal mass doesn't much alter performance. With respect to an optimal range of horizontal effective mass, it seems like Bruce Thigpen of ET came to a similar conclusion. ET(which is a result of some rather sophisticated mathematical modeling) targets horizontal effective mass around 35gm-- about as low as can be obtained in a linear arm. On the other hand, at an audio show Franc Kuzma mentioned to me that a 100gm lateral mass is "no big deal."

The lighter-than-stock custom carbon fiber air sled on my Trans-Fi was partly conceived to off-set the addition of front and rear counterweights. The tonearm's horizontal mass is the sum of all moving parts.

I think it's neat that, unlike every other tonearm extant, the vertical mass of this one can be varied without changing horizontal mass, or vice versa.

Mark Kelly/Quiddity posted elsewhere that he was working on a front counterweight, but had issues with resonance anomalies that occurred when the weight was positioned at a nodal point along the arm wand. In my arm I've attempted to prevent this by hanging the counterweights on separate cantilevers detached from the headshell. Of course, by plugging the headshell directly into the pivot bearing there is no "wand" to resonate per se, other than the headshell itself. Absent a wand, this provides an opportunity to hear the resonant behavior of the headshell itself."

neo

[dlaloum]

It behaves and measures like the 4g damped/stabilised unipivot it is...

Definitely does not like mid compliance carts, loves true high comp.

[neobop]

It seems like Terminator would benefit from reduced horiz mass, probably with carts of any cu. 

Interesting comparison of the AT Art 7 vs DL-S1 after this mention.  The Art 7 is based on AT-50 ANV limited edition LOMC and is more sophisticated in design and implementation.  It's also more expensive, around $1600 from Japan.  Both these carts have a miniscule output .15mV (DL-S1) and .12mV. Both have non ferrous cores or air core coils.  The DL has 33 ohms impedance while Art 7 has 11 ohms and apparently lower inductance also.  It's the higher impedance/inductance of the DL that can interact badly with many preamps. I keep reading about people loading it around 20 ohms to tame high freq aggressive sound.  This is because a tremendous amount of gain is required and because the inductance, relative to output, combines with shunt capacitance and can cause ultra high freq oscillation/overload.  This manifests as intermodulation distortion hence the unusual loads.

The sound signature of these is DL-S1 natural, musical type more like the 103 sound.  It has an aluminum/special elliptical stylus and despite high cu/low VTF, seems to like med/low mass arms (12 to 16g).  I haven't heard the Art 7, but I don't think it takes much imagination to guess why it smoked the DL (according to evaluation).  Art 7 has a boron/LC and virtually all performance aspects were superior.  If you prefer musical, natural 103 sound, you should love the DL-S1.  I think it should work better in limited bandwidth preamps.  I couldn't listen to it with my AHT, had to use other phono pre. 
neo

 

[neobop]

When I read this in the VE thread I was a little surprised:

"One manufacturer who builds tonearms talks about there amazing technologies of arm damping that seem to counteract the laws of physics. Basically, on these arms you use any compliance cartridge you like, simply by adjusting the dampening. Poppycock! Damping schemes will not change the fundamental tonearm resonance, nor would it be preferable to damp that resonance even if possible. What you want to do is allow that resonance and dampen anything above that fundamental.

The truth being told, the materials chosen by this manufacturer in its tonearm wands means that what they are selling is a medium mass tonearm leaning towards lower mass. It is a less expensive arm to manufacturer, substantially so. This was the design goal. This type of arm however is not favored in the current market inundated with low compliance moving coils carts. They don't even publish figures for the effective mass of the arms.

So, out comes the viscous fluids, a sprinkle of magic marketing pixie dust and ... we have a new marvel of audio engineering. Something that we are told does the impossible. An arm that accepts ANY cartridge. Umm ... Not so.

I have tested (both in measurement and listening) six of these arms with seven different compliance cartridges. In all cases, regardless of the "damping tuning" the arms would resonate at the calculated frequencies based on compliance & combined masses. I calculated the effective mass of the arms based on material science and measurement. The damping had no effect on the fundamental tonearm resonance. What it did affect was bearing friction and a reduction or increase (depending on setting) of induced energy into the arm board. This did have a very subtle effect on the sound. I didn't say it was a god or bad effect. It just changed the sound.

Unfortunately, many people have bought into this companies nonsense and as a result believe it sounds good. It doesn't and never will, and not just because of this damping scheme. Other choices made to reduce cost have been incorporated in to the design. Equally wonderful magical engineering has been applied to these inherent flaws as well."

Ghostbusters?   
neo

[dlaloum]

By now, anyone with a serious interest, who is following these threads, should have followed the various links and references and be getting an understanding of what damping does.

No one has ever claimed that damping shifts the resonant frequency - it merely diffuses and distributes its energy  - if you look at a damped resonance the sharp bell curve becomes a lower and broader "bump".

The substantially reduced amplitude of the resonance leads to a substantially reduced amplitude of associated harmonics, and thereafter a substantially reduced amplitude of associated intermodulations....

In reality there would now me lower amplitude but broader bandwidth harmonics and intermodulations. - However once the amplitude drops low enough it effectively disappears below the noise floor.

At what point does that happen? dunno.....

The downside of damping is that it introduces a source of resistance to movement, and therefore as the arm/stylus attempts to track the groove, it will at times introduce a delay, leading to another type of "scrubbing" of the needle, as it is momentarily delayed on the track and then catches up.
This can affect PRAT, and is a good reason to minimise damping - but not a reason to eliminate it!
The tricky thing is to work out how much damping is required to reduce resonance associated intermodulation and tracking problems to the effectively inaudible level, so that no more is used than that.....

On the topic of cartridge matching - a much lower resonance than the "ideal" of 10Hz can be fine if the table is well mounted/isolated, and sufficiently internally damped to avoid internal resonances..... 6Hz or even 5Hz could be OK under these circumstances.
Resonances rising above 12Hz are very likely to affect tracking and become audible on the lower registers....damping helps with both of these substantially.

But given all of the parameters involved, it remains  beneficial to match cartridge to arm ....
In the search for perfection the arm that matches all cartridges ideally does not exist - this one is definitely a pink elephant....

It is also interesting to look at other  options used to stabilise cartridges/arms eg: the air suspended LT arms, Dynavector, arms with lateral weights, or even the Grado Longhorn mods - these do nothing in the way of damping, but can help a lot with tracking ... are these inter-related issues also associated with horizontal resonance I wonder?

bye for now

David

[neobop]

The surprising part:

"The damping had no effect on the fundamental tonearm resonance. What it did affect was bearing friction and a reduction or increase (depending on setting) of induced energy into the arm board. This did have a very subtle effect on the sound. I didn't say it was a god or bad effect. It just changed the sound."

I took this, [damping had no affect on fundamental resonance], to include amplitude of resonance.  If amplitude was diminished, then damping did effect fundamental res.  No?  If energy induced into armboard is reduced amplitude, it seems to be an odd way to state it. 
neo

 

[xsb7244]

FYI, the Audio-Technica cartridge AT-ART7 sells on Amazon for $1157.09

[watercourse]

The surprising part:

"The damping had no effect on the fundamental tonearm resonance. What it did affect was bearing friction and a reduction or increase (depending on setting) of induced energy into the arm board. This did have a very subtle effect on the sound. I didn't say it was a god or bad effect. It just changed the sound."

I took this, [damping had no affect on fundamental resonance], to include amplitude of resonance.  If amplitude was diminished, then damping did effect fundamental res.  No?  If energy induced into armboard is reduced amplitude, it seems to be an odd way to state it. 
neo

That's my reading of it too, and I have the same questions.

[Wayner]

Damping always changes the effective mass of the tonearm, because any damping material is going to add mass to the arm, and that will change the resonance frequency.

Wayner

[neobop]

Damping always changes the effective mass of the tonearm, because any damping material is going to add mass to the arm, and that will change the resonance frequency.

Wayner

That would seem logical for most kinds of damping.  Even an external silicon trough/paddle (KAB) or fluid on the bearings (Jelco) should raise MOI and therefore eff mass?  In practice it only seems to work that way if damping material adds weight to the arm.  If you put a 4g outrigger or sorbothane on the headshell, you'll raise eff mass approx. 4g.  If on the other hand you use damping fluid on the bearings or externally, eff mass remains virtually unchanged and only amplitude of resonance is lessened - spread out over a wider range of freq.  If too much fluid damping is used, arm bearings are impeded and sound becomes dead.

The question is, would this raise eff mass?  I think eff mass remains unchanged, but movement is hampered due to overdamping.   It's an interesting proposition.  Like throwing a baseball underwater, your arm works the same but the fluid impedes movement.
neo

[dlaloum]

That depends on the type of damping - if we are talking Low frequency stylus compliance/arm matching - then no it doesn't - the fluid damping troughs, em dampers etc add negligible mass to the arm.

If we are talking high frequency internal damping of the arm, then yes it does...

But some (much?) of the HF resonances internal damping is trying to eliminate are generated by intermodulation of the low frequency resonance (and its harmonics).

The other (primary) sources of resonance are tonearm flex (500Hz to 1500Hz roughly) , and headshell/arm interface (circa 150-250Hz).

Although internal damping of the arm has its place, I would prefer to start by working on the cause... I think the LF damping is far more critical - then in 2nd place look at what can be done about the arm tube resonance (internal damping, heatshrink, etc...) - finally the headshell interface - which is the most intractable as it may require an arm with integrated headshell...

I think the reason many arms get "over damped" is that the damping is limited to internal and nothing is being done about the LF resonance.... so you end up with excess mass without resolving the core problem.

Another advantage of high compliance designs - they push less energy into the arm, generating fewer vibrations/resonances - so if one can use a LF damping solution + minimal arm damping (to keep mass low) I think the end result is likely to be better...

[Wayner]

Fluid damping via the Jelco (Audioquest) method, puts the brakes on the vertical movement of the tonearm. Perhaps it affects the resonance of the arm, but the damping is back by the pivots.

Fluid damping via the KAB trough restricts the horizontal sweep of the tonearm, aiding in it's ability to resist skating of the arm. Again, it certainly may affect the resonance, but to a very small margin.

If energy is to be removed (by absorbing unwanted resonances), it must be turned into another energy form (such as heat). Personally, I think it's actually necessary for the tonearm to absorb energy generated by the cartridge. It's pretty much like the"tail on the kite", which gives the kite it's control. Would an arm made out of completely absorbent material even sound good? There is lots of energy generated by the cantilever assembly, more then the cartridge would ever need to generate a signal. While heavily damping an arm will tame down some of the excessive, dynamic energy of a highly modulated signal, it will rob from those faint signals, signals that bring the micro-details to vinyl, which in my opinion, is the reason vinyl is the superior media.

To that end, damping an arm can be a slippery slope and any DIY attempt that is not "un-do-able" will almost certainly bring unhappy endings.

Wayner

[dlaloum]

Hi Wayner,

I have not yet seen a KAB trough in the "flesh" - but I believe it is based on the SME model...

The SME's hard two paddles, a vertical one and a horizontal one to provide resistance in both axes - the kit apparently also came with several different size paddles for both locations (presumably the same paddles were used in both positions) - so damping levels in either axis could be varied by varying the paddle size, damping in both directions simultaneously could be varied by changing the viscosity of the fluid used (although that was not a standard recommended procedure - they came with their fluid and a kit of paddles) The trough was (is?) deep enough to immerse both paddles (the paddles are small!).

As a result the trough provides damping in both directions...

Designs with pivot based damping a la Jelco (also the JVC, Pioneer and other arms of the late 70's and early 80's)achieve a similar effect by having a viscous oil bath around the pivot and raising/lowering a "damper" into the oil - I think this approach is more easily sealed and adjusted using a dial, so more user friendly and "foolproof".

Having typed the above I then did a search on the internet for images of the KAB trough and Paddle....
It comes with a single paddle which has its wide axis facing the same way as the arm tube, so as the arm moves on its vertical axis, it generates resistances due to its angular motion in the fluid. - It's affect on horizontal resonance would be much much lesser as it is the narrow cross section of the paddle providing resistance...

Just found some images of the original SME trough - it is similar to the KAB but with variable paddle sizes - so no separate vertical and horizontal paddles Like I stated above.... I am getting mixed up with the original description of the fluid damper concept in the Boston Audio Association Newsletter.... (which precedes the SME trough by a couple of years I believe).

I question the assumption about the levels of energy generated by the cantilever. The softer the mounting of the cantilever, the less energy is transmitted... and therefore the more energy is converted to signal.

The more one can hear the needle directly, the more energy is being wasted by transferring to the arm and cartridge body (and from there radiating into the air and our ears).

Another thing of interest - energy parasitically transferred to cartridge/arm rather than coils/magnets is not linear in frequency...  it tends to vary by frequency - so the frequencies that gets turned into signal are reduced at certain points as the energy is reduced, resulting in a "trough" in the frequency response.

High compliance low damping designs like the Grado's should suffer from this minimally - low compliance  designs would I expect suffer from it most. (but the Low Comp designs would be matched with heavier arms, having a much higher "damping budget"....)

I continue to wonder whether the myth of the "over damped" arm is due to damping, or whether it is due to additional mass (of the damping materials), and therefore a shift in the primary resonance?

At some point I need to play more with the damping on my electro damped JVC and see what effect over the top damping settings have on the sound!
So far I have always either followed the recommended settings of matching Q damping to VTF, or setting it at half to 3/4 that amount based on trackability testing using test records....

I really should get more scientific about it, but that takes a serious chunk of time that I have not got right now. There was an interesting analysis of damping done by luckydog a couple of years back, including models/spreadsheets, measurement methods, and discussion of the "ideal" theoretical level of damping, how to measure it etc... (on VE)
Based on that thread, it would not be difficult to measure and analyse damping - just takes a bucketload of meticulous OCD style time....

I do not believe that one can "over damp" an arm tube... obviously the arm must remain rigid to execute its function, but beyond that a perfect arm should be totally inert (or as close to that ideal as possible).
No robbing of signal here - any part of the cantilever energy that enters the arm, you don't want getting back to the cartridge/cantilever AT ALL - it would then appear as distortion....
On the other hand excess damping of the arm motion (per fluid damper) - that is an area worth exploring, but I have seen no science / theoretical discussions of this aside from the LD thread I mentioned above.
There is a B&K white paper from the mid 70's looking at tonearms/cartridges and measurements that looks at cartridge and arm resonances... "Audible effects of mechanical resonances in Turntables" presented at AES in 1977....worthwhile reading! - it does not cover damping.

Further - in terms of robbing a system of faint micro details, it seems to me (theoretically speaking) that low compliance highly damped (cantilever suspension - an essential corollary of lower compliance) designs would be the worst in this area - yet many of the highly regarded TOTL MC's are in fact Mid to Low compliance, and high compliance examples are now the exception....

more (much more?) food for thought?

bye for now

David

[Wayner]

I believe that a cartridge certainly can be over-driven(by the source), (or at least the phono preamp can be). I have played with soft mounts before, and IMO, made the cartridge muddy, because it had no firm mount. So in effect, the cartridge moved in its mounting position. Of course, there is no such thing as the perfect machine, and the efficiencies of the cartridge to convert mechanical energy to electrical energy vary from cartridge to cartridge, installation to installation. because the arm does draw off a certain amount of energy and phono preamp designers know this, they kind of guess at the required "head room" needed to prevent their preamp from over-loading. But the real question is "how much headroom"? Too much and the noise floor rises, too little and the amp over-modulates. Then the question arises, was the over-load because of the cartridge, the arm, the preamp or the source?

Much like life itself, it's all about balance. Too much of a good thing is bad. Funny how too much of a bad thing isn't good??? But the real solution for us mere mortals is to understand the careful balance great vinyl playback requires.

While the physics of it all (at least in part) eludes many of us (myself included), there are physical things that I have learned over the years with tools and experience of TT behavior. While we talk about a 10hz wave (that would be about 110 feet long) that would interfere with a 9" tonearm is debatable, I do enjoy discussions like this one, tho Me thinks it's over the top of my head and I have no tools or base line to measure any damping that I may try. The only tools I have are my 2 ears.

Anyway, in the end (beer 30) I will sit back, pop a beer and listen to some more vinyl and not worry about arm tube resonances (at least for awhile).

Wayner 

[*Scotty*]

dlaloum, I agree, a completely non-resonant arm-tube would be my ideal as well, also a completely non-resonant cartridge body.
Audio Technica cartridges have a much more neutral character and a better recovery of detail when the cartridge body has damping material applied to it or an external wood encasement is fitted like the Clearaudio MM offerings.
Anytime you can hear the phono cartridge singing along with the music something has gone very wrong indeed.
Scotty

[neobop]

This does not necessarily follow.  The softer mounting of the cantilever usually coincides with lower VTF = less needle talk? 
Wasted energy is not a primary concern.  This is a mechanical process used to excite an electrical generator.  What is of primary concern is resultant electrical output regardless of efficiency. 
The transfer of energy is never going to be 100% efficient.  It's the job of the cart designer to voice the transducer so the end results with test arms (those likely to be used) meet design goals. 

IMO overdamped is no myth.  The best example I can think of is an SME V on a vacuum table with too much arm damping and too much vacuum applied.  It sounds dead as a doornail.  Acoustic instruments lose all their sustain.  The cure is to turn off the vacuum and adjust the arm for optimal damping.  Then over use of the vacuum can be readily heard and adjusted appropriately.  This might be a bit of an exaggerated example that includes the table, but the arm damping much be adjusted to cure the disease.

To my way of thinking you're looking at it the wrong way.  If the mechanical transfer is never going to be 100%, where does the excess energy go, stay in the cart to shake things up?  Instead of reflected back to the headshell/cart, why not dissipate it?  Give vibrations a one way ticket to either be converted to heat by a mass like a counterweight or arm pillar or into the base.
neo

Edit:  Perhaps I overstated my opinion, but I see it more as directing the flow of excess mechanical energy in a way that interferes less with the electrical signal.

http://www.stereophile.com/interviews/pierre_lurne_audiomecas_turntable_designer/index.html

Pierre Lurne:

"The different parts of a turntable or tonearm should always be simple and as compact as possible. By doing so, you avoid vibration problems. When you have too many pieces, there's too much decoupling. And if you have too much decoupling, at the end of the story, you cannot understand what is happening on the disc. Loosen every screw on a turntable, for example, and the resultant decoupling means that the vibrations can't follow a path.

"It's the same in tonearm design. An important point of the design is that you must have a path for the vibrations in the arm. I used a unipivot bearing in the Model 1 for that reason. You need to choose a single path for the vibrations to leave the system, in effect to be grounded to earth. If you have two points, it is possible for the vibrations to return by the other one. With just one point, you have a mechanical diode; you say to the vibrations ~'go that way.' And you can then start to control what is happening in your system.

"Similarly with the counterweight. For years there has been a big debate about whether it is better to have a rigidly mounted counterweight or one that is decoupled. For a long time I preferred the fixed counterweight; otherwise, again, you don't know what is happening in your mechanical system. A decoupled counterweight may be good at certain frequencies, but the overall sound might not be as good as you expected."


 

[neobop]

This is from the next major post:

"The Control of Energy In Turntables

Understanding the movement of energy and applying that knowledge correctly in a turntable design is extremely important. There are times when we want energy to "flow". Other times we want it to go away as much as possible. So the selection of materials and especially the combinations of the same is tantamount to a well performing turntable.

In modern turntable design there seems to be a trend in building tables that use a great amount of coupling. The idea is to transfer vibration away from the stylus/groove interface point. This is good thinking, but how that is accomplished is varied and so do the actual results. A very common idea is to couple one thing to another and hope the energy will be absorbed.

Take the case of a turntable like a Rega RP1 or other similar designs. Here you have a tonearm coupled directly to a slab. Also attached to this slab is the platter bearing. The idea is all the vibration, all the forces in the tonearm and the noise from the platter bearing are to be coupled to the slab. Also the slab is coupled directly to the shelf or stand by spikes. So the energy is then supposed to go out of the turntable from the slab into the shelf or stand. Does this work? You'd think it would by the common audiophile belief system. However, (and here's the catch) the mass of the slab is too low and the materials used in it do not present the correct resistance to vibration. Instead what happens is the bearing noise is transferred to the tonearm. The energy from the tonearm goes down into the bearing. In addition any vibration from the shelf transfers up into the slab. As a consequence of this "Coupling Gone Wild" you get a crazy hedonistic party of vibration from every which way.

This is why you hear about so many after market isolation products for Rega tables. However these tables are popular. Why? Because of the widely held belief amongst many, who heard about the wonders of coupling. If spikes work on speakers "because of coupling" it must work on turntables (and everything else). Sadly using coupling in this manner is actually counterproductive for sound and music. And the ideas are drawn from the incorrect conclusions made from the aforementioned loudspeaker application.

In reality a balanced approach would be to use coupling and damping in concert to achieve true control of vibration, noise, resonances and other forms of mechanical energy."


"Some Specifics on Resonance and Vibration

Vibration can be induced into an object. Resonance is where an object wants to vibrate at a specific frequency as result of its mass and shape.

First let me clarify something I said about fluid dampening in a particular tonearm in my first post. This was relevant to the fundamental tonearm resonance (which I will refer to from this point on as "Fr"). I said that using fluid damping does not change the Fr. This is not totally accurate, it does lower it very very slightly (about 1 or 2 Hz). However, fluid damping does not make it possible to use any compliance cartridge on this one tone arm. The Fr phenomenon still exists and one needs to know the arms effective mass to calculate it properly. The fluid damping does one important thing, it does increase the damping factor in the cantilever/armature mechanism of the cartridge. However this is really most important in a high compliance cart with low mass arm type setup when you are using low tracking forces. In this tonearm however the idea, badly implemented, is supposed to stop Fr from occurring. This it cannot do without first changing the laws of physics. What it does do is mask some tracking problems by damping vertical movement in the arm. The arm is a badly designed and fiddly uni-pivot. To keep it somewhat stable the damping was added (instead of designing a proper uni-pivot or a normal bearing). But they can't say that so they came up with this bogus explanation for it being there.

So what is fluid damping anyway? It is using a viscous fluid to absorb energy. It can be performed at a specific rate by using a fluid of a specific viscosity. It can be done simply with a cup and a spoon. Put some viscous fluid in a cup and move the spoon around. The more thickness the fluid has the more resistance is presented to the spoon in the direction it is moving. This is a form of damping. Take this example in miniature. Imagine a tiny "spoon" attached to a tonearm, with a tiny "cup" with thick fluid in it. It is easy to visualize how this could dampen resonances or vibrations in tonearm. It is used in some designs for a variety of damping applications.

It is also used in turntable suspensions as well. The Oracle Delphi MKVI, for instance, uses little cups and spoons to dampen lateral (side-to-side) movement of its sprung suspension. Other designs use fluid damping in other ways. However, the shape, size and orientation of the "spoon" and the precise amount of viscosity of the fluid are critical for the specific application. It makes using this damping scheme difficult to calculate (yes ... there are ways to calculate this and the formulas are complex). It is even more difficult to use the trial and error methodology. While it works in variety of application, it is very difficult to design. It can also be very messy for the end user.

So are there easier ways to achieve damping and coupling in tonearms. Of course there is. Let's talk about tonearms resonances and vibrations and some ways to control them. First I should point out there are certain resonances that are not avoidable, like Fr. However, we need to control it. In this case putting Fr in a range where it has the least amount of negative effect on the sound or function of the arm/cart system and the phono stage. This is why it is important to match the right compliance cartridge to a tonearms effective mass. The combination of the cantilevers stiffness combined with the mass of the cartridge (and hardware) and the effective mass of the tonearm, combine together to produce a single frequency or note of resonance. By doing the math, you can put the system into resonance in a range of frequencies where it doesn't cause problems. This happens to be between 7hz to 10Hz for the most common tonearm cart combos. These things will always resonate when brought together, but by careful math and understanding you can control these resonances where they end up doing little harm.

As I mentioned earlier, coupling can be varied by materials. By combining various materials you can contour the amount or type of energy transfer, like down the length of a tonearm. Tonearms are funny things. You don't want them to vibrate yet you want to be able to transfer the energy created by the stylus away from the cartridge. So you need the best of both worlds. Damping and coupling. It's a delicate balance. One way it can be achieved is to use different materials along the length of the tonearm. For instance, a rigid aluminum cartridge mount connected to carbon fiber wand, attached to another pieces of aluminum at the pivot. This can in effect control vibrations and at the same time transfer energy down the arm and out through the bearing. This is accomplished by controlled transfer. Meaning there is a transition between different materials which changes the speed at which energy travels over time. In physics this described as a materials mechanical impedance. These abrupt changes prevent specific resonances from being setup, while at the same time still moving energy away from the cart. In a way, this is using less than perfect coupling to produce a certain amount of damping. Creative, eh? The Graham Phantom II and the Origin Live tonearms use this principle to good effect.

The shape of the arm wand can have an impact as well. As I mentioned early in this section, the mass and shape of an object helps determine its fundamental resonance, the note it naturally vibrates at. Think of a vibraphone key. A straight rectangular hard bar that when struck excites into resonance at a particular note. Because of its non-varying shape and consistent mass over its length it produces a very pure tone or frequency with few harmonics or overtones. Objects can also resonate at a numbers of notes at the same time, simply by changing its shape. Take a bell. For the most part it is a straight cylinder, but then flares out at the bottom. It has a primary note or frequency produced by the straight cylinder, but the flare is added to give it overtones; extra notes in addition to the main one. However if you make it perfectly conical it doesn't seem to want to make much of a sound at all. That is because over the length of a cone the mass and size continuously change therefore no specific resonance can occur easily (except over its length).

A tapered arm wand, like you see on some straight wands from SME, work to vary the speed of energy transfer and the reduction of resonances by changing mass along the route. The narrow end of the taper has lower mass, the wider end has more mass. And this change in mass increases linearly, it is different at every point as you go down the length of the wand. They tend to not resonate at any given frequency. Yet they manage to move energy well.

Curved arms are supposed to do the same thing, however in actuality the effect of curvature has only a small impact in controlling vibrations and resonances. It was utilized years ago when there where much fewer choices in materials compared with today. So back then it was an improvement. Today it is unnecessary. Curving an arm is not as important anymore in this regard because we have a wider range of materials that do a much better job on their own, without the need for curves.

One other note. Detachable headshells impede coupling and therefore have a tendency to reflect energy back to the stylus. This is why they fell out of favor. They have very pronounced negative affects on numerous aspects of music."

neo

[neobop]

This discussion about energy management got me thinking about stock feet vs spikes and coupling vs decoupling support shelves. 

Lately I've been using a Denon 1250 with spikes on my wall self.  I replaced the spikes with the stock feet and got more bass.  This is the lightest table I own. I'll have to experiment with the other tables.  In the past I seemed to get a cleaner sound with spikes on the KD-500.

Another question is about coupling and decoupling.  Ancient wisdom was that inverted cones (points up) under a shelf would decouple it from the supporting structure.  In the other room I have end tables with such an arrangement on top of them.  I'll have to try something else, like maybe sorbothane under the cones or footers instead. 

The beginning of the last quoted post was a basic explanation of mass coupling/decoupling.  I thought it unnecessary.
neo

[dlaloum]

This does not necessarily follow.  The softer mounting of the cantilever usually coincides with lower VTF = less needle talk? 
Wasted energy is not a primary concern.  This is a mechanical process used to excite an electrical generator.  What is of primary concern is resultant electrical output regardless of efficiency. 
The transfer of energy is never going to be 100% efficient.  It's the job of the cart designer to voice the transducer so the end results with test arms (those likely to be used) meet design goals. 

You are partly right - basically the vibration energy transfer between two materials is related to their density/mass/hardness - the more different the two materials the less gets transferred and the more gets reflected... the more similar the two materials the more gets transferred and the less gets reflected.... This is common wave behaviour, applies to optics as much as to vibration in Turntable materials.

Now we look at the cantilever - hard rigid material - it is held in place by its suspension rubber doughnut - soft material -  the softer the material of the suspension the less prone the system is to transmit energy through it (the transmission actually results in refraction - ie change of frequency - same as in optics) - the firmer the material the greater the tendency to transmit through it.

The proportion of the energy passed through it will be proportional to its "firmness" with transfer increased as the suspension is firmed up.

Additionally the suspension materials tend to be firmer at certain frequencies and softer at others - so the amount of energy transferred (or reflected) will vary by frequency.

I don't believe (gut feel here) - that a stylus on its own has enough surface area to lead to "needle chatter" - it needs a "sounding board" - this is provided either by the cartridge or by the stylus holder surround....(plastic piece holding the cantilever/suspension)....

Some other related thoughts on damping - something like the Signet TK series cartridges has hollow areas in the body on the sides, these would be good areas into which to place a damping compound potentially - keeping in mind that this will increase the mass of the cartridge (and most of these are high compliance so added mass is an issue) - Potting the interior is already a well known improvement mod.... and I believe that Neo has done this a few times.

I believe the benefits of potting are due to an increase in the amount of energy that is transferred from needle to body being converted into heat (ie: damped)
The possible negatives with this approach: - the energy that is not converted into heat is returned to the cartridge body, at an altered frequency (refracted) - and usually with a lower amplitude (as part of the energy has been converted to heat) - if the new frequency(ies) is more easily drained off by arm/plinth then thing go real well - but if the new frequency(ies) happen to coincide with a resonance of the arm / headshell / etc... then it may make things worse..... this vibrational stuff is NEVER SIMPLE!!!

The problem is not necessarily the wasted energy... the problem is that the energy drawn off from the signal is not flat in frequency - some frequencies are absorbed more than others.
So the signal then leaving the generator has been altered by the non linear frequency losses.

The second issue is of course what happens to that lost energey (hence the paragraphs above).

The principles are critical in setting up a turntable....

1) Use hard materials with hard materials to transfer energy, hard materials with soft materials will reflect energy back into the source material.
2) When vibration transfers between materials of differing density (actually speed of sound in the material) then the frequency changes.
3) Certain materials are good at converting vibration energy to heat (eg: sorbothane) - but they do so only within certain frequency ranges, and their effectiveness reduces massively outside these frequency ranges
4) Materials often have a combination of properties - for example sorbothane - at some frequencies it behaves as a spring - transferring energy and altering its frequency as it passes through, at other frequencies it behaves as a solid with reflection/refraction properties related to vibration, and finally there is a range of frequencies for which it is very good at converting vibration to heat.

Design tricks include:
- identify problem vibrations
- use materials selectively to move the vibration to a damping layer, and to alter the frequency of that vibration so that when it reaches the damping layer, it is within the damping layers optimum band for conversion to heat.
- use the refraction/reflection properties of materials to drain the vibration from critical areas and keep them in the damping layer (refract towards the damping layer, reflect back towards the damping layer)

Which brings us back to things like cones and soft sprung feet, or soft rubber/sorbothane mount feet.

There is no one solution - as the turntable becomes a system linked to its environment (listening room, walls, floor, building) - and therefore your problem frequencies will be different in each environment.
It is possible to massively over-engineer a turntable to attempt to copy with most of the possible install environments... but then it gets expensive!

And the same problem exists at the stylus/cartridge/arm/plinth interfaces - each choice (compliance, cartridge materials, arm shape, etc...) affects all the others.

This is what makes vinyl so much more interesting (intellectually) than digital

bye for now

David