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In Reply to: Re: cantilever armboards posted by user510 on May 5, 2007 at 11:59:23:
Gotta disclaimer this right off the bat. Much of this heads into physics and territory perhaps better travelled by science dudes. My approach is trying to understand it in simple terms if at all possible. From what I've seen, heard and experienced in audioland & diy-audioland....First the complications. Numerous tables that are highly respected --Brinkmann, Yorke, Verdier, Sme 10---- do one or two things* that are at first glance counterintuitive.
Like out-boarding the tonearm to an arm-mount on a platform extending away from the central record transport.Ultra-overkill massive construction, careful attention to mass-balancing, and then patient testing may be how these all come to terms with what is a little counter-intuitive in the first place...
But --- What's more steady and reliable as a platform to trace micro groove-modulations--- the deck of the ship, or the outboard platform ...?
And ---what's the tendency, where will heavy motor vibrations most often tend to travel to--- from a large central mass to a smaller outboard mass ? I think so.
(Conversely, travelling motor rumble will tend downwards if it meets continued resistance in the direction of the armboard, ie, if there is continuous high-mass material encountered in that direction. Tendency then would be, given 'lossy' footer scheme, downwards into the shelf or rack.)Surrounding and balancing that mass with the same mass / rigidity that supports the rotating lp strikes me as the only way to assure reliable data retrieval from the spinning groove.
In all kinds of data-carrier-data-reader setups, sometimes people find that there's a little too much 'there' there, in the groove or pitted compact disc.
Or too much artifact, too much noisefloor, errors in tracking, timing, etc.
What come to mind as "remedies" are things like roll-off filters for lp use, or dither schemes for cd.
People even go to extremes with thick platter mats, sponge-inserts on cartridge mounts, or tonearm-mounts that are compliant or 'wriggle'.....Although the initial impression may seem like they're beneficial, these fixes are add-on patches...
.. bandaids that indicate that the hardware/software interface was noticeably lacking in the first place.Anyway, you can't judge anything from a photo, so no criticism meant of the table in the orig post...
But it's hard not to wonder, for example.... what's the best place to write a vacation postcard --from the solid footing of the swimming-pool deck, or, from the diving board..?
Assume, for the sake of the analogy, that they're having the Forbidden Lambada Dance Contest that night, so the whole hotel is pulsing, as if there were a big motor rumbling underfoot .......
What feels the underfoot rumble most intensely -- the deck, or the cantilevered platform of the diving board..?
And whats going to happen to your mango-rita-fuzzy-sunrise with the umbrella ?
J.D.
(( * the other I-don't-get-it thing about these well-regarded tables, though not the sme, is that they are top-heavy and some are even wider at the (rotating) top than they are at the base. Another solidity / rigidity / mass-balancing moment of huh ?..... In my opinion. ))
*
groove
Follow Ups:
While I do agree that the deck is more stable than an outboard platform, I couldn't help but notice the implementation of the armboard on the Teres that Steve shows. The first thing that I saw was how it was tightly interfaced with the main body of the turntable. Its stepped design helps to insure that. Would the armboards of some other manufacturers fall short in this area? Probably.My personal turntable has a three pound stainless steel armboard mount that is bonded into the plinth on three sides, so it goes without saying that my belief is that the integrity of the interface is the most important consideration to be made when considering interchangeable armboards. Fortunately, Teres and some others address the problem the quite nicely without an integration as apparent as one that is surrounded by plinth. Their "diving boards" aren't subject to flexing, so it becomes a question of design tastes, rather than effectiveness...in my opinion
Is that when I modeled a turntable with the tonearm mounted to the plinth it picks up the resonance of the table every time.Whether the resonance is motor based or accoustic feedback the resonance is there. It may be down 16db or more but it is right there.
With a cantelevered armboard the resonance is choked down many more db. The only requirement is to rigidly couple the armboard and that is the same as gluing up a bunch of layers of plywood or MDF.
When Mannfred88 posted that my Rek O Kut outplayed a 3k dollar Sota Saphire rig I think that should have caught a great deal of attention. Cantelevered armboards work extremely well and should easily outperform any direct mounted tonearm.
Of course strapping a tonearm on 3 lbs of steel....that would be interesting to measure! No bets on that test!
My new LP-34 will have a cross cantelevered armboard. I wish I could patent the idea, but it is far too basic and pedestrian. The top piece of the platten will be maple and the tonearm will attach to that point.
The idler interface will be accoustically decoupled from the maple.
We will see how this flies..... I am told that the devil is in the details.
If I can get the table together by next weekend, ScottRT and MintVinyl can tell you what they hear.
well said!i do think that some designs eschew a plinth, so they are then left with the only choice of having a separate arm pod or an armboard that is extended via some cantilever design.
if we are optimistic, we trust that these manufacturers decided that the removal of the plinth was better for the sound than the introduction of the cantilever -- or, at least, that their implementation of the cantilevered arm board addressed some/all of the negative elements.
having heard at least 2 of the turntables in the list you presented (and not having been impressed by them), i'm not certain the statement in the above paragraph is true -- but we can imagine a situation where TT design choices were not made for the aesthetic but for the aural impact.
in the system pictured in the original post, the cantilever seems like an afterthought to accommodate an arm that was not accounted-for in the original design. if we were looking at a 'plinth-less' design, then it might make more sense (at first glance). clearly, though, the TT in question was designed to be used with a heavy plinth.
It is used to accoustically decouple the plinth resonance from the tonearm.By using dissimilar materials, or different thickness of the same material you can attenuate some or most of the resonance.
Cantelevered armboards are not afterthoughts. They are solid engineering and they work very well.
I think that it is easy to get the wrong impression with regards to cantilever armboards. One such impression is that because cantilevers are known as one form of spring, that all cantilevers are springs. Not so. A cantilever can be made into a rigid unmoving mass......such as a Teres or Galibier armboard...or architecture drawn by F.L.Wright, etc.Another is that because cantilevered armboards are not as physically thick as the rest of the plinth/base, that they somehow lack integrity.
I say how much mass in an armboard do you need anyway?
Further, what about acoustic resonance egress? Vibes traveling out of the arm and into the armboard. Would not this be facilitated by presenting said vibes with a tapered mass, thinner, then thicker material to flow into rather than one solid mass to reflect away from?
If I understand Analog Guy's comments correctly his concern is that an outboard perch, such as a cantilevered armboard can result in a "lever effect" commensurate with the distance from the point of attachment, or, to say it in another general way, an increase in the amount of "micro motion" that the tonearm must suffer due to the way that the turntable is situated on its base, floor, environment etc. This might be part of an explanation as to why the Teres is a turntable which favors high mass sitings. Conjecture on my part too.
Agree with your comment that this is an area where the "science dudes" should explore more definitively, or even with any validity. At this point I think what's needed are measurements to support the claim. Don't have any right now. There's just this thing about a Teres armboard that seems to work, is all.
-Steve
"There's just this thing about a Teres armboard that seems to work, is all."...but we don't know how much better/worse/different things would have sounded had the cantilever design not been used.
again, if we are optimistic, the designer(s) tried all routes and selected the one which sounded best - but we know that at least for some TT designs the nod is given to the aesthetic.
while it might be miniscule, i don't think it's conjecture that a cantilevered anything will vibrate more at the "free" end vs. the point where it is attached to something else. this might not matter in some designs, but i think it's hard to argue from a physics perspective -- it's simply a mass located further away from the origin of the vibration.
the ultimate proof is in the sound, and this is all just conjecture not because the scientific theory is lacking but, mainly, because we are not listening to 2 otherwise identical designs but for the cantilevered/non-cantilevered armboard.
Guess I should have emphasized the way around that is obviously used in some tables, like the Teres armboard shown..As mentioned .."Ultra-overkill massive construction, careful attention to mass-balancing, and then patient testing may be how these all come to terms with ..."
In some cases, though, yes, outboard arm-mounts lack physical integrity, as materials, or based on construction / design.
But beyond the 'lever' issue, presented by that situation, my other point is that :
If the armboard represents any lesser a massed physical presence than the mass of the plinth, it becomes a target for motor resonance proceeding from the greater resisting area (mainland) to the lesser resisting area (peninsula).
Until the armboard region of the system represents at least as imposing a resonance-conducting venue as the plinth, it's a path of least resistance . Isn't it ?
In the case of your Teres armboard, the layered & ultra-rigid approach probably represents an imposing roadblock to resonance. Not so the simpler-construction, simpler-material, outboard armboards we see sometimes. (Besides, w/ DC servo beltdrive, there's way less to fear by way of rumble than with an Idler-coupled design..)
J.
I guess the way to proceed would be to arrange a test to measure resonance flow into various armboard schemes, eliminating all the intuitive/instinctive/subjective takes.In the Auditorium plinth pictured I don't think that I see any lack of structural integrity in that particular overhanging armboard. It will be rigid providing the armboard material is of adequate tensile strength. Resonant flow from motor, into plinth, into armboard? Just how much vibration does that Garrard motor emit?
My TD124 motor seems well mannered and quiet, emitting only a soft whir that can just be heard when you put your ear next to it. If I place the probe end of a mechanics stethoscope against the cast chassis in the vicinity of the running motor, I can faintly hear the whir of the motor, just barely. Place the stethoscope onto the plinth next to the cast chassis and nothing is heard.
Another stethoscope anecdote, Teres style.
When I had just mounted the Shelter 501 type 2* cartridge to the 'Expressimo RB250' I noticed some very distinct "needle talk" while playing a record with the amplifier muted. I found this to be interesting so I used a Stethoscope to trace the path of these resonances. With the probe placed to the side of the all acrylic Teres armboard I could distinctly hear the music being tracked through the earpieces. I then followed the resonant path of this "needle talk" with the stethoscope. It traveled out of the RB tonearm into the armboard and down into the acrylic base of the Teres. The further away from the tonearm, the fainter the "music" heard through the ear-piece. This confirmed to me, and other Teres owners, that the cantilever armboard of the Teres was indeed transferring resonances away from the tonearm and into the massive base where it would likely dissipate and die. Possibly the resonance would also flow through the cone footer nearest the armboard mounting joint and into the isolation base. It then struck me as being an efficient armboard in the area of resonance management.Of course there is no similarity of this type between the armboard on the Garrard plinth shown and that of the Teres, which was indeed carefully considered.
-Steve
* The Shelter has a very -stiff- low compliance cantilever and exhibits obvious needle talk.
user510's system
We are talking about reducing resonance by a factor of as much as 4 times. Take a strain gauge and place it against the body of an idler turntable. This will read the mechanical resonance or the physical displacement of the material created by the frequency resonance of the motor and the accoustic feedback from the environment.When you mount a tonearm directly to the plywood plinth there is 4 times more resonant energy communicated to the tonearm than with a decoupled arm board. A directly mounted tonearm board and a rigidly connected cantelever armboard are basically interchangeable. However the cantelevered armboard exhibits less "strain" IF you select the proper materials.
Now you can build a variety of clever tonearm boards. For example, you could build armboards from MDF, Rock Maple, Walnut, Ebony, or Carbon Graphite and you will hear a difference in the sound with each variety of tonearm board. Each of these various materials is actually decoupling the plinth from the tonearm. The materials work differently regarding the frequency resonance and the physical resonance which I would prefer to call "strain."
Mixing material can also help diminish resonance and "strain". I often use acrylic and another material to tune out the resonance.
It is not the mass of the armboard that matters. It is the careful sellection of the material to accomplish the resonance control and strain resistance that matters most in terms of the sound quality of the turntable.
tubesforever's description of the virtues of different materials and cantilevering seem right on the money to me. The armboard depicted here (which is my turntable) is a single piece of cast copper, very heavy. It is secured to the base - which is constructed of all kinds of different woods in various pieces with various voids - via a single heavy allen bolt from the bottom right up through to the armboard.This turntable sounds AMAZING. My previous plinth was no slouch, was 24" wide, and had the 12" arm directly mounted on the armboard. The LignoLab plinth blows it away in every way - more controlled bass, more air, more layering, more PRAT, and just wonderful musical flow pouring out of the speakers.
The plinth was designed for 12" arms, by the way (check the toneimports.com page, or if you can read German, the auditorium-23.de page), so the cantilevered arm board was a conscious design choice. Knowing how these guys design equipment - via listening - I think that, as tubes suggests, they experimented by listening to multiple different materials and constructions until they found the combination that best dealt with resonance.
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