It's an Ibeam with CLD properties from the looks of it.
It looks like the mechanical attachments are fixed to the plates and not the foam.
The foam could be polyurethane, melamine (Basotect, Magic Erasor), or possibly aluminum foam.
That was my guess too. I cloned it by sandwiching three layers of thick double sided tape using two thin steel sheets. Bottom steel sheet has two screws separated by half inch and accepts the cartridge. The upper steel sheet can have one screw or two depending on headshell design.
The most important thing is that two steel sheets do not have any screw "short circuiting" them. The layers of foam isolate the two sides. Of course better foam will do a better job. I just used what was available on hand.
I can’t answer that Hiten.
Their very detailed service manuals do not show the internals of the counterweight, nor mention any adjustment.
I haven’t one of the Duals in my possession for to dismantle it either.
George
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Silicone Foam Gasket Material, Silicone Foam Tape | Stockwell Elastomerics
OK. Its going to be some grade of this stuff.
.................
I'm trying to imagine the mechanism of "damping the music." You want an acoustic impedance mismatch between the cartridge and the rest of the mechanism, right?
Ida thought I'd want the cartridge held still relative to tone arm at any frequency
So you want a material that's light, stiff and well damped. Gotta be a composite:
wood/plastic/metal sheet
foam_________
Wood/plastic/metal sheet
I don't think the frequency matters so much as the energy budget, so to speak. The energy generated is small.
The foam layer distributes impact forces very uniformly and they are mostly converted to heat.
The beam itself is really quite rigid in this application, I'd guess. Do you think it could bend or twist in any significant fashion?
In this application do you think the foam could displace laterally? Given the width of the beam?
I think it's a neat concept. Does it work?
Anyone make composite tone arms?
I used to be into this stuff and then there came digital.
Ida thought I'd want the cartridge held still relative to tone arm at any frequency
Well the perfect tonearm is infinitely stiff and a pure mass in 2 planes. Of course we can't have that so we have to deal with wibbly wobbly resonant systems. In normal use in the audio band if the stylus goes one way the arm and cartridge must go the other way. As long as the mass of arm and cart is orders of magnitude greater than the stylus assembly all is good. But a damper such as we are discussing if not 'solid' at audio frequencies would allow the cartridge to move relative to the arm which would not be good.
On the train this evening was thinking about silly putty as that has some of the wanted features. https://en.wikipedia.org/wiki/Silly_Putty sure enough it is silicone based.
I have forgotten too much about this stuff and need to do a lot of research. Where is SY to point us in the right direction when we need him?
silly putty is a non-Newtonian fluid.
some foams are impregnated with silly putty type compounds. the purpose to deal with impact by spreading force over large area
https://www.google.com/search?hl=en..._occt=any&safe=images&as_filetype=&as_rights=
my hunch is that's possibly overkill for this application
https://www.google.com/search?hl=en..._occt=any&safe=images&as_filetype=&as_rights=
i gotta run
the cartridge man isolator and for that matter the Rega RP8 is just alloy clad 'foam board' used in the sign industry. its dirt cheep. you also get diabond which is a solid core version as well. but like all bull manufacturers blurt out they make it sound like some fancy unobtainable magic mystic material that they have specially made by pixies and fairies.
The stylus scrubbing that occurs from the cartridge bobbing around is like flutter in a tape deck, and would be FM. The magnet/coil relationship could be pushed out of its optimum alignment and cause other forms of distortion as well, harmonic or IM. If you look at a frequency modulated sinewave on a spectrum analyzer, FM at low modulation levels starts out with only two sidebands. While that would look like AM, it is nonetheless in this case FM. Also, magnetic cartridges being a velocity pickup, the relative groove velocity increases as the stylus scrubs backward and decreases as the stylus scrubs forward. This could lead to slightly higher cartridge signal output on the ‘backward’ scrub and slightly lower cartridge signal output on the ‘forward’ scrub, and result in some AM artifacts. I’m not sure that the RIAA EQ in the preamp would negate this? Cartridge bobbing from warps or LF resonance can create a number of forms of distortion in the signal. The FM can’t be filtered out.
Ray K
Browsed the internet. Found this two links. (1) (2). It seems there is a metal leaf spring with weight on one end and screw to adjust their flexibility. Tuning the mass. Not sure though. Still interesting to know why not use plain counter weight ? May be they damp the wide band frequency range resulting in loss of liveliness ?I can’t answer that Hiten.
Their very detailed service manuals do not show the internals of the counterweight, nor mention any adjustment.
I haven’t one of the Duals in my possession for to dismantle it either.
George
Best regards.
That's what I see and it's similar to what I find brush up/down up a Stanton cart.
I reviewed all my LP rips with test tone recordings.
There is no AM.
Inspecting the files in the time domain, the record eccentricity and the arm/cart resonance cause amplitude undulation of the test tone envelope but they do not cause amplitude modulation (there is no ‘modulation factor' to speak of).
I eat my words and I apologize to Lucky, to diyrayk and to anyone else for the noise I generated.
Yes Bill. It reduces the peak of the arm/cart resonance and reduces the effect of record vertical wraps.
Alas, as you have seen it has no effect on the peaks caused by the record eccentricity.
We shouldn’t forget the two other ‘humble’ functions of the brush, namely groove cleaning and continuous discharge (to ground) of record static electricity. (On another post I may show some screenshots of the effect of static discharge through the needle, it’s not very nice)
George
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