***Now in a turntable how it plays out is that instead of being scary or dangerous, it works out as a coloration: the platter must be as tightly coupled to the plinth via its bearing as possible, in turn the plinth must be absolutely rigid and acoustically dead while coupling the platter bearing to the base of the arm (which in turn should have no play in its bearings). Any divergence from this formula results in coloration.
The reason is simple: if the platter has any other motion other than rotation (for example a slight up and down that might be imparted from the plinth due to room-borne vibration), if there is any difference between that and the base of the arm the cartridge will compensate (since the stylus has to stay in the groove) with stylus motion and therefore a coloration.
So if the arm is sitting on a separate structure from the plinth, it is open to motion in a different plane and/or frequency as opposed to the platter and plinth. You really want it to move in the same plane and frequency as the plinth so that whatever that motion is can't be interpreted by the cartridge.
I am often amazed at how poorly understood this concept is. ***
This concept is a gross oversimplification and isn't thought through. Airborne vibrations will be imparted to the platter (record), plinth, and arm at roughly the same time. There will be a delay as these vibrations are then transmitted from one to the other. This results in additional smearing/coloration. It could also result in greater amplitude and additional coloration. This is not better. It's worse, assuming the pod approach is well done and resists cross coupling. There will still be some cross coupling through the base, but it's less likely to produce cross coloration if the base resists vibration transmission and the pods are mass coupled. It's a fallacy to assume that vibrations appearing at the main bearing are best transmitted to the arm. ***According to them the separate tonearm pillar version sounds more transparent and quieter because of the isolation of the tonearm from the TT.*** No good reason to assume this is false. Regards,
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Lewm, What is "proper connectivity" ? The physical (mounting) relationship between platter and arm must be maintained. The plinth or chassis must be heavy, rigid and not prone to transmit vibrations. Why? So vibrations or movement of the bearing does not get transmitted to the arm? So these vibrations get transmitted and the arm moves in concert with the platter? It's nonsense. Regards, |
Atmasphere, ***This is actually easy to measure! We do it with a silent disk, cut on our lathe, which is much quieter than normal vinyl. All we have to do is place the turntable in a room with speakers playing loudly and then measure the output of the cartridge. The fact that turntables that employ a separate arm pillar are more noisy then 'tables with a proper plinth is easy to see on the 'scope.*** This statement is unexpected and seems counterintuitive, at least to me. Could you describe the tables measured? If you've seen photos of Halcro's TT101, do any of the measured tables reflect that level of isolation? Regards,
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This seems like an anecdote - interesting but lacking specifics. What about the arm pod details? First we're told, **All we have to do is place the turntable in a room with speakers playing loudly and then measure the output of the cartridge.** Then, **As to sound pressure- we get about 90-95db of noise going on when mastering. The vacuum system is enclosed in its own chamber, but still makes noise when in operation.** All of the above? You're checking cuts while this vacuum system is in operation. There are also vibrations coming from the vacuum motor which is making 90 - 95dB of noise while in its own chamber? The obvious question - did the separate arm pod have the benefit of the isolation platform as the platter? I'd also like to remind everyone, assuming the Technics 1200 was a MKII or later, this table was designed to play in extreme noise, in excess of 100dB is not unusual. It would be interesting to see a more scientific test. If a plinth mounted arm is quieter, at what room SPL does it become so, and for exactly what plinth, arm, and pod. fleib
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Pani, I was about to start a pod style build and now find this thread particularly frustrating with lack of any hard information. What was this pod that Atmasphere used and how is this motor noise relevant? We assume, but don't really know if the separate pod was even used on the same isolation platform. **According to them the separate tonearm pillar version sounds more transparent and quieter because of the isolation of the tonearm from the TT. My concern is whether seperating the tonearm from the plinth would result in a lesser coherence in sound ? Isnt sharing the same platform results in a more well-timed, coherent presentation ?** Timing and coherence were not addressed. Perhaps other people who use or have used both styles of arm mounts could comment. I suspect results vary greatly with individual application. Apparently the people making and selling the table you're considering think it sounds quieter and more transparent with a separate arm mount. Their conclusion about quieter does not conform to Atmasphere's rules. Think it's just a sales pitch to sell separate arms/pods and more expensive set ups ? With lack of evidence to the contrary, I would take their statement at face value. Maybe you should get in touch with them and ask them to elaborate about these differences with these tables and its significance. Regards, |
I think there is a fly in this ointment: **The reason is simple: if the platter has any other motion other than rotation (for example a slight up and down that might be imparted from the plinth due to room-borne vibration), if there is any difference between that and the base of the arm the cartridge will compensate (since the stylus has to stay in the groove) with stylus motion and therefore a coloration.** Air borne vibration will hit the record/platter directly, as it also hits a plinth and arm. Any such vibration transmitted via the plinth will arrive after the event. How will this insure coincident behavior between arm and platter? This isn't an automobile where both wheels are being turned at the same time. This is transmission of movement through time, and record rotation does not stop. It seems like this is the same old formula for sprung tables where movement must coincide. Evidence or lack of, points to high quality and good execution as the winner. Think I'll go with Frank Kuzma and Torqueo Audio on this one.
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Thekong's suggestion brings up an issue we haven't addressed. What exactly is the source of this vibration, and what is its relevance? Atmasphere, you talked about a motor producing 90 - 95dB of noise in the room and described the vibrations as room borne not air borne. This sounds more like a seismic event than music playing, as if a bus or truck drove down your street and shook the house. We not only have 90+dB of noise, we also have the motor vibrations which produced the noise. If you consider the principle involved, that is any extraneous arm/platter movement must coincide, then why is using a plinth more desirable than a base? The best plinths are those that do not transmit vibrations, but now we want transmission? I think the answer is in the execution. A "properly" constructed pod will not allow movement in a different plane. The base will serve the same function as a plinth only with more affective isolation. A seismic event is shaking the entire table and platform and your set up was unstable with the pod. Regards, |
Thekong, The original statement: **if the platter has any other motion other than rotation (for example a slight up and down that might be imparted from the plinth due to room-borne vibration), if there is any difference between that and the base of the arm the cartridge will compensate (since the stylus has to stay in the groove) with stylus motion and therefore a coloration.** I suspect it doesn't matter. This seems to be more than sound pressure waves hitting the table, and we might as well be talking about table mounting in general. Why is a plinth superior in maintaining identical movement between arm and platter? Either proximity, or lack of rigidity in table or pod coupling to the base. We now know of at least a couple of prominent designers who have used the pod approach with "superior" results. No offense Ralph, but your expertise is with tubes and modifying an old Empire table does not qualify you as a table or arm designer. I've modified tables and mounted arms, but I don't consider myself ....... Regards, |
bdp24, A table with a suspension is a different story. Regards, |
Atmasphere, From your post near the bottom of page 1: **As to sound pressure- we get about 90-95db of noise going on when mastering. The vacuum system is enclosed in its own chamber, but still makes noise when in operation.** Unless that means something other than what it says, you're changing your story. I understand your engineering principle, but I question the significance. Will a massive plinth transmit small main bearing movement to the arm base? Excite a tuning fork and touch it to a big rock and the vibration is turned to heat. Even if it does transmit it, the resultant arm movement will occur after the main bearing event. What about micro movements you allude to? Not likely, and with the same time consideration. Sound pressure waves hitting the platter are also hitting the plinth and arm at virtually the same time. To say that a plinth will insure coincidental movement between cartridge and record also doesn't make sense with regard to time. The impact on the record player is instantaneous and rotation of the record is continuous. Regards,
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Lew, That's BS for reasons already stated. Micro vibrations wouldn't make it from record or main bearing to the arm, with a massive plinth. With a flimsier plinth the movement of platter and arm must coincide perfectly for this principle to be valid, and that is not the case when vibrations originating from the platter are transmitted through the bearing, then the plinth and to the arm base. Surely you jest. Regards, |
Lew, **To wit, there would be a great deal of movement of the LP surface, mediated by the suspension, that could not be followed by movement of the tonearm pivot, and this would generate spurious signals at the cartridge/LP interface. On a more micro level, this principle is operative in the relationship between any plinth, suspended or not, and any arm mounting system.** Not true. On a micro level the vibrations would not make it between platter and arm with a high mass "dead" plinth. Part of the reason such plinths sound good is because they resist vibration transmission. You think this engineering principle holds true under any circumstance. It does not. It holds true if and only if part of the table is in extraneous motion and the other parts move with it simultaneously. That is motion other than normal platter rotation. High mass tables are more likely to be immune to such motion. **Reed used to make an armpod.
I believe Nandric (Nikola) had the first one ever made by Vidmantas. I was looking for the resonance research data that was prominently displayed on his website, which showed a visual of the different resonances and their paths (integrated versus isolated parts). The info had a lot of cool lines and colors differentiating the two, with information clearly supporting the armpod.** Regards,
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**As to sound pressure- we get about 90-95db of noise going on when mastering. The vacuum system is enclosed in its own chamber, but still makes noise when in operation.** That's a direct quote. Now we learn the motor is at the end of a long hose. Does it produce 90-95dB of noise in room? If so, is this noise + mechanical vibrations? The measurements are based on this story and now it looks inappropriate. This is the same as the music coming off a turntable? Looks like we have no relevant measurements. fleib |
**Fleib, if I can offer a bit of advice, try to craft your posts in a way that it is not obvious that you are simply trying to make the other party wrong by ignoring facts. You will have greater success.** My posts were based on the information you supplied or didn't. How can I ignore facts which weren't offered? You were repeatedly asked details about the pod. Did you give them? Assuming your results are what you say, why should we accept this as the last word on this matter? Prominent table/arm designers have reached different conclusions. You're more knowledgeable than Kuzma, Reed, or Torqueo Audio? Reed site had a set of resonance numbers which favored the pod. They're gone now, but your anecdotes are fact? Atmasphere, you've made your point and I think everyone understands it. Why don't you go back to tube design or mastering? Unless we can figure out why results differ, there's nothing more to say.
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