Arm Damping

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MikeyB456
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Arm Damping

Post by MikeyB456 » 12 Jul 2019 21:06

I'm trying to get my head around damping, and how it helps control/improve vinyl replay.

Some arms - eg SME3009, Mission 774 can have damping 'troughs' into which a paddle is dunked. I presume this principally damps horizontal movements and resonances, but possibly does some vertical also?

Some arms - eg Jelco 750 - allow damping fluid to be added specifically into the horizontal pivot. I presume this principally damps only horizontal movements and resonances?

But some arms - eg unipivots like the Hadcock and Mayware - have damping in both planes, as the whole pivot assembly is surrounded by damping fluid.

So which dimension is more important, and why?

nat
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Re: Arm Damping

Post by nat » 12 Jul 2019 23:39

Damping can perform differing functions. One is controlling the arm's response to record warps, keeping the arm from bouncing around. The other, more important in many people's view, and utterly unimportant in other's view, is damping resonances in the arm caused by the energy put into the arm by the cartridge. Those who value damping cite clearer and more stable imaging, smoother frequency response, and the blackness between notes. Those who disdain it sometimes point to the problem of overdamping, which smooths things out to the point of dullness. Others simply don't hear any effect (I guess).
Given that both horizontal and vertical components are involved in the stylus's motion, both dimensions matter.
With unipivots, damping is desirable not only for the normal virtues of damping, but also to keep the arm from acting wonky when handling it. Those who have nerves of steel may not care that when the arm is being lifted or lowered by hand onto the record, it flops completely over, but most people appreciate some slowness in motion.

analogaudio
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Re: Arm Damping

Post by analogaudio » 13 Jul 2019 00:18

I agree, both dimensions matter however it is common to find the horizontal is damped and the vertical neglected.

As you may already know the subject can be studied from the physics standpoint by recognizing the cartridge suspension to be a spring and the arm assembly to be a mass, and springs with masses attached vibrate and usually have a single frequency at which resonance occurs. This behavior comes under the topic of simple harmonic motion. The arm is in a state of constant vibration stimulated by the cart suspension as it follows the various sources of low frequency energy, disc surface ripple, very low frequency musical energy, disc warps, acoustic feedback from loudspeakers, and just to rub salt in the wound the LP microgroove RIAA playback amplification adds 100 times gain to the bottom octave to recover the bass suppressed at the disc cutting stage. It is a miracle the system works as well as it does!

When the cart suspension receives an impulse from any source the arm/suspension response will be some kind of oscillation at the resonant frequency, usually around 10Hz. How long the oscillation persists depends on the amplitude and also on the damping, which may be absent altogether in a design having very low friction bearings, or decaying quickly without overshoot in a well designed and damped design. These situations are identified as under-damped and critically-damped. Damping is defined as the removal of energy from the oscillating system and there are often several ways to do it. Tonearms often use the frictional drag of the paddle in viscous fluids.

There is a collection of engineering articles on this and many other subjects in the anthology published by the Audio Engineering Society called Disc Recording and Playback volume 2. The website is aes.org and a download is available for about $40, worth every penny if you are curious about the development of LP playback from the mid 1950s to the mid 1980s.

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Re: Arm Damping

Post by pivot » 13 Jul 2019 03:23

Fairly complete description of the SME 3009 damper assembly and what it does. Note most of the damping effects the vertical plane and it is adjustable by changing paddles.

https://www.theanalogdept.com/images/sp ... %20200.pdf

Also very complete discussion of the KAB damper for the Technics 1200 arm. KAB damper is very similar in function to the SME and does most damping of vertical movement.

https://www.kabusa.com/damping.htm

When in doubt RTFM

Google around and there are articles on the topic out there.

I added the damping assembly to my SME IIIs. It really makes a difference to the sound.

Not difficult to experiment with damping - see here: http://www.enjoythemusic.com/magazine/bas/0809/

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Re: Arm Damping

Post by chgc » 13 Jul 2019 03:32

How about cantilever damping— cactus?

H. callahan
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Re: Arm Damping

Post by H. callahan » 13 Jul 2019 04:39

On a stereo record the groove walls contain vertical and horizontal modulations, so damping of both directions can be beneficial. But as far as i know vertical modulations cannot be tracked as good as horizontal, so as it is said they try to avoid or reduce vertical modulation during mastering to make the record track better on average gear.

Also when the paddle is in the damping fluid there can be some sort of vertical damping, depending on the viscosity of the fluid. If you put a rod into a glass of honey and pull it out again there will be some drag, though the rod only is moving up and down.

So damping vertical movements might not be as important as horizontal, when the paddle only is a rod there also will be some vertical damping - and because of record warps the vertical damping shouldn´t be too big. If it is, the upside of the cantilever can contact the cartridges body at the beginning of a warp and at the end of a warp the stylus can loose contact to the groove.
That´s probably why a lot of arm-dampers seem to ignore the vertical plane.

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Re: Arm Damping

Post by MikeyB456 » 13 Jul 2019 12:03

Hi Pivot, thanks very much for the links. Most helpful. I've been pondering how to try a DIY solution, and there we have one. Not exactly elegant, mind you...

Pity there aren't more 'bolt-on' solutions like the Kabusa for other arms.

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Re: Arm Damping

Post by pivot » 14 Jul 2019 02:52

H. callahan wrote:
13 Jul 2019 04:39
.........................................
That´s probably why a lot of arm-dampers seem to ignore the vertical plane.
Did you read the links posted above? Most of the damping action of both the KAB and SME 3009 damper add ons are of vertical movement.

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Re: Arm Damping

Post by Sunwire » 14 Jul 2019 05:58

MikeyB456 wrote:
12 Jul 2019 21:06

Some arms - eg Jelco 750 - allow damping fluid to be added specifically into the horizontal pivot. I presume this principally damps only horizontal movements and resonances?
The Jelco 750 and the similar Premiere MMT have a hemispherically shaped "well" on the top of the pivot that holds a small amount of damping oil. The cap that screws into this well has a bottom that has a shape similar to the bottom of the well, but smaller. When the cap is screwed down, the oil is squeezed between the cap and the bottom of the well. This layer of oil damps both vertical and horizontal movement.

MikeyB456
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Re: Arm Damping

Post by MikeyB456 » 14 Jul 2019 10:23

Hi Sunwire,
I don't quite see how that could work. Surely there wouldn't be any vertical movement in that bearing anyway?

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Re: Arm Damping

Post by H. callahan » 14 Jul 2019 12:47

pivot wrote:
14 Jul 2019 02:52
Did you read the links posted above? Most of the damping action of both the KAB and SME 3009 damper add ons are of vertical movement.
I cannot see pictures on the KAB-link and because of record warps a paddle shouldn´t be as damping on vertical movement as it is on horizontal.
And i said "a lot seem to ignore", not "all do ignore" the vertical plane.

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Re: Arm Damping

Post by pivot » 14 Jul 2019 17:00

Name some of the "lot" of designs that ignore vertical damping? I can think of exactly one. All damped tonearms I have personally set up or owned damped both horizontal and vertical.

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Re: Arm Damping

Post by pivot » 14 Jul 2019 17:21

.....how paddle is shaped controls the amount of damping in either plane. The face of the paddle being wider increases the vertical damping on the SME 3009 damping kit. That's why there are three different paddles in the kit. The cross section of paddles is nearly constant so horizontal damping is changed very little. The KAB damper appears to work the same. Damped unipivots arm like the Mayware and Grace 714 (owned both) have damping in all planes. The original Well Tempered (set up a couple Well Tempered but have not played around with the latest "golf ball" variants) has more damping, it seems, in the vertical. I know one tonearm that, by design, damps only in the horizontal.....curiuos if you know it.

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Re: Arm Damping

Post by nat » 14 Jul 2019 17:25

I believe it is precisely because of record warps that damping the vertical component is added to arms even if the designer or modifier isn't convinced of the value of damping for audio reasons. Controlling the oscillation/pumping of the arm in situations where the mass of the arm and the compliance of the cartridge aren't perfectly matched is pretty obviously a good idea.
Damping doesn't resist the arm moving slowly, which it needs to do to track the record and to go over warps. Instead it resists rapid motion or change in motion, which is why it can affect resonances in the audio and arm mass/compliance resonance ranges.
Any paddle or cup kind of damping will affect both horizontal and vertical motion. Damping the actual bearings of one dimension and not the other would give damping in only one plane. The electronic damping used by Denons and Sony Biotracers and others may only affect vertical motion, but I am not well enough acquainted with the systems in use to be confident in my guess.

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Re: Arm Damping

Post by H. callahan » 14 Jul 2019 17:40

pivot wrote:
14 Jul 2019 17:00
Name some of the "lot" of designs that ignore vertical damping? I can think of exactly one. All damped tonearms I have personally set up or owned damped both horizontal and vertical.
I said SEEM to ignore and one that comes to my mind should be the Rock by Townshend.

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