Adding any material to your tonearm cavities will significantly change the effective mass of the arm. Be careful. Sand is completely out of the question. Also, it is not true that "the more acoustically dead, the better". There must be a balance struck between damping and "liveliness" or your music will be dead. This is not something for a newbie to be fussing with, unless you have money to burn.
The Teres 255 platter has the chambers filled with lead shot. Adding a liquid has been thought of, and it is a problem with sealing the chambers against leaks.
I have done a number of mods to arms and tables. Search the archives for my threads on mods. |
http://www.audioasylum.com/index.html
Go to Audio Asylum, click on the vinyl discussions, and pose your question there. There are a lot of do it yourself, and down right cheap things that can be done to improve things. Also, not all the people here advise spending huge bucks for things. I've found quite a few of them that are downright helpful, some have sent me things for nothing, and many have taken the time to be helpful. Every forum has those that tell you to "sell your crappy stuff and buy what I have" Stay away from them. |
As you suggested,I went back and read one of your threads on tonearm tweaks which discussed adding lead fishing weights protruding from the vertical axis. I am not an audio expert but I did study college physics enought to make me wonder that such a small weight attached so close to the axis could have a measureable effect. Did you actually calculate the change in resistance to angular momentum that would result from this to determine its significance? It seems to me that a much longer outrigger arm would be needed such as a rigid wire attached perpendicular to the arm with the weights at the end. Inertia would increase in proportion to distance of weight from the pivot point.
My question concerning sand in the arm, which you said was "out of the question" would also increase the inertia of the arm and with proper counter weighting, would be indistinguishable, in terms of the physics, from your outrigger,in the horizontal dimension. It would also increase inertia in the vertical direction. (But there may be other reasons why sand in the arm is a bad idea).
It seems to me more physics is need here. It is interesting to hear that someone is "blow away" by a tweak but the audio press is full of too much of this hype to give it credibility without solid analytical justification. |
Putting sand in the arm to increase the arm's mass would require a change in cartridge, because the same cartridge cannot work well with a low mass arm and a high mass arm, as I understand it ... the arm's mass must be appropriate for the compliance of the cartridge.
It's one thing to balance an arm with a counter balance, but increasing the arm's mass would appear to be more detrimental than helpful to me, possibly even damaging. |
As I understand it, compliance is how much a cantilever bends in response to the weight of the cartridge. I was not proposing to change the weight, just the mass. Mass and weight are very different things. With counterbalance a cartridge can exhibit no weight but be quite massive. |
Jyprez. The increase in vertical mass is the problem with adding the sand. So it is distinguishable(in terms of physics) from my tonearm mod, because my mod does not affect vertical mass. I assure you if you load your arm with sand, you will be unhappy with the result. Warp tracking will be hideous.
Yes, I calculated the horizontal mass increase in my tonearm mod. And the distance of the weights is 1.75" outside the center of the pivot on both sides, so there is an increase in inertia from the length of the outriggers, as well as just the pure mass. This mod works, and is calculable, and proven in testing.
As far as credibility goes, you may do as much analysis of it as you like. It is not for sale, so it makes no difference to me whether anybody likes it or not. Several testers as well as myself are enjoying some significant benefits from this mod. Very few others even showed any interest. So no hype is necessary, because anybody that wants it can make it themselves, and if they don't want it, I don't care. I have given up trying to convince people. Now I just post my information, and leave it at that. |
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Jyprez, you're correct in your description of compliance, and all would be exactly as you describe if the record was not turning. As soon as the record starts turning it is not perfectly flat and the cartridge is deflected up and down by small amounts all the time. This is where mass becomes very important, since the higher the mass the higher the inertia to the deflections. If the cartridge compliance is designed to be able to withstand the deflections of a low inertia tonearm it will not work at all well when you add sand and massively increase that inertia.
At best you'll change the resonant frequency of the tonearm - cartridge combo, almost certainly to the detriment of the sound quality. At worst you'll ruin the LP, the cartridge, and possibly even the tonearm bearings. |
Ah, Ok so you are (both) saying that the cantilever needs to move in the vertical plane as well as horizontal for music reproduction (or is it just because the record is imperfect and potentially warped?)? I had thought that stereo reproduction only depended on horizontal movement and that the record grooves were flat in the vertical plane (except for that expirement back in the 70's with Quadraphonic). Certainly you are right that if a cantilever must go up and down in response to the grooves, more mass would be damaging to the record. If, however, it only moves horizontally, more mass (not more weight, just mass) would not damage the grooves. |
Since the groove walls are angled, there is inevitably some stylus movement in the vertical plane. But there are very big vertical movements when a warp in the record is encountered. A large mass will actually leave contact with the record after being "thrown" up in the air by the warp. Then it will come back down at some later point of the record. This is generally not desireable. Typically, designers will make the arm as light-mass in the vertical plane as is practical. This normally also sacrifices horizontal mass, and was the reason for my tonearm mod, which separates and allows different mass in the horizontal and vertical planes. When an arm is not designed to have independent vertical and horizontal masses, then there is an inevitable compromise between light vertical mass for warp tracking, and heavier horizontal mass for cartridge stability. One or the other will suffer from the compromise. I promise that I did my homework. |
Jyprez ... you're right ... if it only EVER moved horizontally there would be no problem. But that is never the case, even if the record is not warped. There may not be large vertical deflections, but there are small deflections on all records (at least all that I have).
BTW Twl is way ahead of me on turntable knowledge, but I did recently read an interesting web page on compliance, tonearm mass etc etc ..
http://www.gcaudio.com/Archives/tonearmcartidge.htm |
TWL, If there is a large horizontal oscillation, as happens if the cutting path spiral is eccentric, then the large horizontal mass, as you describe it, works against the stability of the cartridge stylus pressure and skating.
BTW, I think that the term with which you have been struggling to describe the principle of "horizontal" and "vertical" mass, is Polar Moment of Inertia in whatever plane that you want, horizontal & vertical.
I have no doubt that you did your homework on this and am contemplating making the same modes to my Rega 300 on the Alex IV. I do have some (2 or 3) quite eccentric LPs and it might be interesting to see if the increased horizontal polar moment will resonate with the frequency of the eccentricity.
Salut, Bob P.
salut, Bob P. |
Bob, I believe the mod as I applied it is forgiving of the larger movements of record eccentricities. And it seems to have no effect on the slow tracking of the spiral groove as it traverses the record. I have no "wildly" eccentric records in my collection, so I don't know if this will be a problem for the arm with my mod, but I am considering the effectiveness on a "normal" LP to be of greater importance than its performance on a "defective" LP.
Yes, I'm aware of the Polar Moment of Inertia, thanks for reminding me.
I'd like to hear what results you get, especially on the really badly eccentric records.
I'd also like to remind you that the benefits of this mod will become smaller in effect with higher compliance cartridges, and will be of no use at all with very high compliance cartridges. I have tested cartridges up to 15cu with Rega arms, and they are still getting benefits from this mod. How much higher in compliance you can go, without losing effectiveness entirely, is unknown to me at this time. I would say, though, that any cartridge that would normally be considered a good resonance match with a Rega arm, would receive some benefits. |
TWL, upon rethinking my concern for horizontal resonance at the frequency of eccentricity, that shouldn't be a problem, as the frquency will be either about .5Hz or 1Hz and the mass would really have to be high for that to occur. Also, I should have mentioned that my cartridge is a BPS. |
