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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?

dogberry

Showing 4 responses by fsonicsmith

fsonicsmith's avatar
fsonicsmith
934 posts
 

Well, the 18th century oak chest wins over all other considerations! It's worth more than all my hi-fi and records.

Don't take me literally. I meant to ditch it as the base for your turntable. Looking at the photo you posted the chance of the two pods being in the same plane as the platter surface when seated on different planks making up the top of the chest is quite small. If the shaft of the tonearm is not "laying" in the same plane as the top of the platter then you are stymied before you begin to worry about the other aspects such as excessive vibration. 

fsonicsmith's avatar
fsonicsmith
934 posts
 

You asked for help. The rest of are not there and can only go off of the available information. I gave you my very best guess and very questionable opinion. 

fsonicsmith's avatar
fsonicsmith
934 posts
 

@mijostyn For once I am in agreement. I have said it. elsewhere in this forum. Even the pivoting leaf type of mount found on many turntables such as this one is significant compromise. It offers versatility if you change tonearms and easy adjustment of P-S and yet at the same time invites detrimental vibration. One of the most knowledgeable guys in the industry who builds plinths admitted as much to me at Axpona one year. VPI has been designing turntables with aluminum bridges upon which the tonearm sits to facilitate their VTA on the fly adjustment system for many years, again a compromised design. The ultimate effect on performance may approach the minuscule, but at the price level asked it is not appropriate. SME has the best approach to adjustable P-S-the rock solid "sliding sled". 

All of this is just my humble op. 

 

VPI - Avenger Plus Turntable

fsonicsmith's avatar
fsonicsmith
934 posts
 

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?

What says me is that you should ditch the oak chest and replace it with a more dense, mass-loaded, and precisely flat base and then use one very dense and massive tonearm pod. The concurrent thread about the OMA audio turntable designs demonstrates this approach. 

 

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