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Tonearm microphonics

When I have the volume at my normal level & tap the arm (not whilst playing vinyl) it is slightly amplified... Is it possible to significantly reduce/eliminate this?

Current set up - Roksan Xerxes 20plus, Origin Live Encounter tonearm (thin cork ring at the base) with Lyra Skala.

Apologies if this is a stupid question!
128x128infection
moonglum
619 posts
 
Atmasphere is right to point out that there are adverse side effects where the geometry of the disc is not uniform and flat when external damping in the form of silicon goop is applied.
Not only does it damp resonance but it also exerts drag on the arm's movements not unlike extra friction in the bearing. this means if the arm has to weave from side to side or follow vertical undulations there will be slower reaction.

However, here's the kicker : even if the disc was drilled perfectly centrally and was perfectly flat there would still be a problem because the tone arm must "sign" across the disc as it still must follow the inward "spiral" of the groove to its centre.

Therefore Stringreen's suggestion was extremely sensible i.e. if the arm seems naturally well enough damped, try to run it without damping fluid.
bdp24's avatar
bdp24
9,452 posts
 

In his original review of the Well Tempered arm, and in Bill Firebaugh’s literature on his arm, Gordon Holt discussed the viscosity of the arm’s "bearing" well damping fluid, and how it allows the arm to freely move at very low frequencies (those of the arm following the groove, warps, etc.), but keeps the arm’s bearing rigid above those frequencies, such that it allows it to act as a normal mechanical bearing, but with very low friction, and no bearing rattling or chatter

The Townshend Rock turntables damping trough behaves in the same manner; warps are "slow" enough to not impede the movement of the arm in response to them (up and down), and the same with groove eccentricity (left and right). Those frequencies are very low, far below the lowest contained in recordings. At audio frequencies, the viscosity of the damping fluid in the trough is heavy enough to "lock" the front of the arm in place, just as an arm’s bearings do at the arm’s rear. The result is the tightest, cleanest bass I’ve ever heard from LP’s. LP surface noise is diminished as well, and violins take on a smooth sheen, their timbre sounding organic, not electronic, bright, or etched. The resonance-reducing capability of the Rock system also increases the audibility of inner detail (listen to one of the great recordings of the large choral groups Robert Fulton made---every voice is individually audible, or the massed string section of a symphony orchestra) , and micro-dynamics. With the low-level "haze" (that created by uncontrolled resonances in the playback machine) removed from the sound of LP’s, the sound IS more like that from master tapes, the mechanical nature of LP reproduction reduced. Does this sound like a commercial ;-) ?

One interesting thing discovered with The Rock is that it decreases the difference in the sound of arms mounted on it, the damping apparently compensating for the less well-damped nature of cheaper arms.

bdp24's avatar
bdp24
9,452 posts
 
To clarify, the relationship between warp and eccentricity demands on the ability of the arm to follow them, and the frequencies involved in those demands, are a matter of the time it takes the arm's headshell to traverse a warp or eccentricity. If a warp takes the arm's headshell a full second to travel up and then back down, the frequency involved is 1Hz. The same for an eccentricity that it takes the headshell a second to follow left and then right, back to where it started; one second equals 1Hz. If the warp or eccentricity take 0.5 seconds to traverse, the frequency is 2Hz, and so on.
timeltel
830 posts
 
Regards.

Correct me if I'm wrong, I really don't mind.

A cartridge doesn't care where it's signal comes from and if any constituent part of a turntable can resonate, it will. 

Resonance can be either constructive or destructive, airborne or mechanical. Constructive resonances are typically considered to primarily fall in either the fifth harmonic or at the first octave, The enhancement of these resonances are usually considered pleasant, sometimes even desirable (think piano or strings). Destructive resonances may be generated by extraneous mechanical vibration or reflected airborne energy such as sound reflected from walls, a nearby speaker or other objects close by. This may also be described as  proximity resonance.  

Sources of these resonances can be autonomous, sometimes described in terms of Eigen value. Imagine a large, heavy plinth coupled to a light tonearm. If the plinth is energized it will act on the tonearm to some commensurate degree. The tonearm resonates to it's own value. When these resonances couple to resonate in phase and not disproportionate to the recorded signal these resonances may be said by some listeners to be considered as desirable.

Resonances not in phase are said to be destructive. In this sense and depending on degree, damping can generate either constructive or destructive resonances.

Just when one thinks they've a handle on the phenomena and your turntable is performing in a wonderfully synergistic manner, a change of cartridge or headshell shifts mass, nodes are redistributed, phase goes out of kilter and unanticipated boundary resonances return unwanted signals.

The cartridge doesn't care where the signal comes from.


Peace,


  



moonglum
619 posts
 

Dear Bdp24,

Sincere thanks for your excellent and well written post.

I knew that if we “mechanical laymen” poked the problem with a stick for long enough, someone would weigh in with some actual research ;)

I had completely forgotten about the Rock. It is one of the most well-researched turntables in analogue history. If Townsend says that damping works regardless of adverse conditions then that’s good enough for me. :)

Best regards,

Bill.

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