Vibration Question
Warning to the sensitive: involves tonearm pods.
I know this topic is beyond the pale to some, but my tables cannot take a second tonearm (once upon a time, though, they did), and I enjoy variety in cartridges. I have bought four pods so far from Lee Drage at Acoustand, two plain and two with built in micrometer VTA adjustment. But I discover the airspace around the tables is too congested with six arms, as well as introducing some grounding issues. So, as I told pindac the other day, I started to experiment with using two pods per tonearm. Not just a simple 'if one is good then two must be better' but for practical reasons. Firstly, a pod resting on three spikes weighs about 10lb, but it doesn't take much pressure on the distal end of the arm panel to cause it to tip. One can spoil a carefully set up alignment that way, and if it continues tipping a disaster could happen. So, I thought, why not place a pod under the distal end of the tonearm panel, and prevent that happening?
But then a second thought came along: if the second pod were firmly coupled to the panel, I would double mass and damp vibrations even more. That's a bit theoretical to me, as my oak chest weighs ~350lb and I can stamp on the floor next to it and not disturb a playing stylus. But rigidity is rigidity. So I asked Lee if he could make me a double ended panel with an SME mount centred in the middle. Roughly, like this:
He agreed, and pointed out I would have to forego the VTA adjustment, unless one were to place a screw at each end! I can use the SME mount itself to adjust VTA. though, so that's OK.
Here, finally is the question: he thinks I am simply introducing twice as many vibrations (external, I think he means) into the tonearm by having it rest in two sites on the oak chest, and that I would be better off having one end of the tonearm panel free-floating. My view is that rigidity is paramount, and if a built-in tonearm on a table is firmly coupled to the table then I am moving a bit closer to that ideal by having a firmly coupled chest-table-pod system. What say you?
@lewm @mijostyn Thank you, gentlemen, for your (expected) answers. But, the question? One pod better than two, or vice versa? @danmar123 Certainly, but it is the same thing as an Acoustand with built-in mount. I like an Englishman with a lathe, and you seem to have found me another. Maybe it was the way my father spent his evenings in his workshop, or maybe it was Neville Shute. |
@OP You don't necessarily want to be coupling your tonearm mount to a large vibrating surface like the oak cabinet. There is mass in your arm pedestals but no damping. The only real benefit from the proposed arrangement is not having the arm on a cantilever. As already suggested, you would be better putting the entire turntable and arm setup on an isolation platform. |
My own experience of Standalone Pod being used and as design put on paper has been for the Tonearm to be directly anchored to the Pod. Cantilever Arm Boards have for a long time caused myself to ponder if the support method is prone to flexion. The fact that numerous TT Producers are now adopting this method, suggests it is a satisfactory application, or might be a very cost effective solution to engineering requirement. Most recently I produced a design given to a friend for a Cantilever Tonearm Board to be produced from Panzerholz and added to a P'holz Plinth. The Cantilever Board will enable TA's up to 14" to be added and be used to carry out comparisons between a selection of TA,s. In your own design as shown on paper, the typical method that a pod is used has changed to the Structure now being Two Piers and a Lintel/Bridge. With this design, my query about flexion will remain. The unknown energies are now being transferred through two anchors/piers and there may be a cross talk between transferred energies that add a new energy that could be transferred to the styli. As an alternative proposal and if the Bridging Arm Board is to be tried out, it might be worth expanding thought on the concept and see if a Longer Bridge could be used, one that over sails each Pod. The design will allow for additional positions to connect the TA, and if looked into a design may be achievable that would enable up to Two TA's to be set up on the one structure? |
