Active versus Passive Isolation Platforms for turntables

[PeterA]

I have read through most of the WBF threads about isolation platforms. There is now a fairly active discussion about the Herzan active platform. Rather than take that thread off topic, I would like to start another thread specifically about the differences between active and passive isolation platforms and their effectiveness under turntables. One observation has been that many of these platforms were designed specifically for scientific instruments likes microscopes and not designed for audio devices which may have internally generated vibrations created by movement within the component. I have read claims that active devices can attenuate such component generated vibrations, but I have not read an explanation about how this is achieved.

Could users and designers experienced with both active and passive devices discuss the different approaches to isolation and how or why one approach may be more effective than another when used under audio components? I am particularly interested in the potentially different requirements needed to isolate turntables and those that generate internal vibrations and how they may be different for suspended and non suspended turntables.

 

[PeterA]

Here is a photograph of my suspended SME turntable on a pre loaded Vibraplane and an explanation of how I think the various different types of vibrations within the system are addressed:



Floor-borne vibrations: There are two steel lolli-columns directly under the front legs of my source component rack in compression between the floor joists and bedrock floor in the basement. There is little if any floor bounce. The rack is a very stiff, rigid DIY birch ply and cherry wood structure supporting 450 lbs of steel on the top shelf. The 150 lbs Vibraplane is preloaded with a 150 lbs steel ballast plate plus the 115 lbs of turntable to approach its design load of 275 lbs.

Air-borne vibrations: The SME has two thick steel frames separated by four suspension towers. This thin profile lessons the surface area for air borne vibrations from the speakers to effect the system. The mass of the turntable absorbs some of these air borne vibrations.

Internally generated vibrations: The motor sits on the lower shelf separated from the platter by the drive belt and four suspension towers. Motor vibrations are drained down and away from the structure through four steel ball bearings at each foot below the suspension towers. The mass of the platter, the record clamp and soft platter surface work as a system to absorb energy generated by the stylus and record contact while cartridge vibrations travel along the arm tube through the bearing into the massive arm board and upper shelf.

The overall approach is one of energy drainage paths, absorption by compact, minimal surface area mass, and air isolation. I don't know how active or passive isolation could address the internal vibrations, or air borne vibrations, so those are handled by the design of the turntable itself. For floor borne vibrations, I added an external passive device. I don't know if or how an active device would be more effective. Note that the motor controller is also up on the Vibraplane to avoid floor borne vibrations.

 

[spiritofmusic]

Peter, I'm in a bit of comms w Jarek of Stacore, and they're providing an interesting approach of isolating pretty far down but a lot higher as well
His argument is active isoln does not address these broadband full spectrum vibns
The product combines a modern take on Vibraplane pneumatics/springs so isolating low down and higher up, slate chassis which as a mixed natural product breaks up vibns further, and ball bearings which aid isoln further
This is in comparison to a purely air based passive shelf from Speirs and full active electronic from Speirs w the Stacore priced exactly midway btwn the two

 

[ddk]

I don't know how active or passive isolation could address the internal vibrations, or air borne vibrations, so those are handled by the design of the turntable itself.

I tend to agree with you on the turntable design, that's where many of the issues need to be addressed. I use heavy 1" or thicker plate on top of very heavy solid steel table so my experience is relative to that and not a standard audio rack. What one is used to and the design of the actual tt are things that need to be considered in this discussion if trying to figure out effectiveness. If the vibrations are airborne I don't see how any type platform or rack does anything, you need to encase the tt.

david

 

[spiritofmusic]

Dave, and Mike Lavigne, thanks for pushing me away from active isoln for my tt on a flexy suspended wooden flr
My flr is pretty rigid, but it cannot match the inertness of my prev concrete flr, esp at a span of 18x50
I'm minded to go the Stacore Pl Advanced route, 230lb (!) of modern interpretation Vibraplane pneumatics/springs w slate shelf and ball bearing lateral plane isolation
At a price point between Speirs air/MinusK and Speirs active price points, a great looking design, and plenty of interesting tech and thoughtful engineering, it could be the go to choice esp for those like me in situations where flr not eminently suitable for active isoln

 

[ddk]

I moved a lot in my life and getting things right took a while every time but you end up learning a lot. Good luck!

david

 

[PeterA]

Dave, and Mike Lavigne, thanks for pushing me away from active isoln for my tt on a flexy suspended wooden flr
My flr is pretty rigid, but it cannot match the inertness of my prev concrete flr, esp at a span of 18x50
I'm minded to go the Stacore Pl Advanced route, 230lb (!) of modern interpretation Vibraplane pneumatics/springs w slate shelf and ball bearing lateral plane isolation
At a price point between Speirs air/MinusK and Speirs active price points, a great looking design, and plenty of interesting tech and thoughtful engineering, it could be the go to choice esp for those like me in situations where flr not eminently suitable for active isoln

Marc, have you seen measurements for the effectiveness (which frequencies are attenuated and by how much) of the Stacore products? I agree, these devices seem promising, but I would like to know more. Do they need a compressor, at what pressure are they inflated, what are the dimensions, etc? Those are heavy units and would need strong support underneath, especially if supporting a heavy turntable.

 

[Stacore]

One observation has been that many of these platforms were designed specifically for scientific instruments likes microscopes and not designed for audio devices which may have internally generated vibrations created by movement within the component. I have read claims that active devices can attenuate such component generated vibrations, but I have not read an explanation about how this is achieved..

Yes this is right, in the lab you have much narrower bandwith requirements for the operation. Who cares what happens past some 100-200Hz? Microscopes do not
You seem to be attach to an idea that an external device will help with internally generated vibrations. Well sorry to say it but it won't. The only thing it can reliably do is to prevent the vibrations from spreading around by breaking its path. One example I've been trying to promote here is to suspend loudspeakers. Try it guys and observe the results

I am particularly interested in the potentially different requirements needed to isolate turntables and those that generate internal vibrations and how they may be different for suspended and non suspended turntables.

I strongly discourage to stack similar stiffness suspensions working in the same direction (e.g. vertical). The suspensions may go into beat oscillations (if their resonant points are close), with actually increased ULF vibrations instead of decreased.

 

[spiritofmusic]

No specs or measurements yet, I'm in the early stages of comms w the guys at Stacore and will ask them to post
They are happy to allow the platform to be placed direct on the floor to situate the tt at low level
Fwiw, when I auditioned the active Accurion i4 some yrs back, the sales manager was happy to pop that on the flr in my apartment
The way I see it is if these devices are overengineered to isolate comprehensively, there should be no reason they shouldn't be able to be used on the flr

 

[Stacore]

Marc, have you seen measurements for the effectiveness (which frequencies are attenuated and by how much) of the Stacore products? I agree, these devices seem promising, but I would like to know more. Do they need a compressor, at what pressure are they inflated, what are the dimensions, etc? Those are heavy units and would need strong support underneath, especially if supporting a heavy turntable.

Peter, thank you! There is no need for a compressor, you pump it with automotive pump and correct the pressure once in 2-3 months, which takes a bout a minute to do.
The pressure depends on the load and is usually in the 2-5(max) bar region.
Yes, we are heavy mass, Basic @ 62kg, Advanced @94kg Dimensions: 580 (L) x 480 (W) x 108 (H) [ mm ] and 580 (L) x 480 (W) x 140 (H) [ mm ] We can also do custom dims.

Hope this helps

 

[spiritofmusic]

Jarek, as you know I'm in some ongoing contact w you
It would be great if you could publish test measurements of what the Stacore is achieving in vibn isoln, esp at freqs below 2Hz
You'll find that this is one of the few areas in the high end where even the most ardent subjectivist like me needs plenty of objective data to secure a purchase, esp when lab grade companies like Herzan, Accurion and Speirs Robertson websites are full of data and graphs

 

[Stacore]

Jarek, as you know I'm in some ongoing contact w you
It would be great if you could publish test measurements of what the Stacore is achieving in vibn isoln, esp at freqs below 2Hz
You'll find that this is one of the few areas in the high end where even the most ardent subjectivist like me needs plenty of objective data to secure a purchase, esp when lab grade companies like Herzan, Accurion and Speirs Robertson websites are full of data and graphs

Marc, the measurements we have taken so far are not in the usual form you see at the lab platforms manufacturers so we decide not to publish them
to avoid misinterpretations. The measurement setup did not allow for that form of the transfer curve. We plan to repeat them in another lab
somewhere in the near future and have the data in more easily understandable format to be able to publish them.
But what I can say is that we do not do 2Hz or lower, nor we feel we have to as we are not designing a microscope platform.
Our resonant points on both platforms are about 4.5Hz unloaded, down to 2.7Hz (IIRC) fully loaded, multiply that by 1.4 to get the lower end of
the isolation region. Lab manufacturers pages are full of data (averaged; real life curves do not look so pretty) because those data matter in the lab.
The figure of merit there is the resonant point, the lower the better. This resembles the "ultra low THD" mania we
are all old enough (I guess ) to remember and all those discussions of 0.0001% vs 0.0000001% which had nothing to do with the sound.
Same here-one fres point or even the transfer curve will tell you nothing about the sound. I would try to avoid making
ad hoc correlations between some more or less abstract parameter and sound.

 

[PeterA]

Yes this is right, in the lab you have much narrower bandwith requirements for the operation. Who cares what happens past some 100-200Hz? Microscopes do not
You seem to be attach to an idea that an external device will help with internally generated vibrations. Well sorry to say it but it won't. The only thing it can reliably do is to prevent the vibrations from spreading around by breaking its path. One example I've been trying to promote here is to suspend loudspeakers. Try it guys and observe the results

No, I have made no such claims about external isolation devices helping internally generated vibrations. I do not see how they can. However, I have read claims that the top plate of the Herzan does detect vibrations coming down from the component sitting above it and attempts to correct for that. I have not read explanations from owners or the manufacturer about how this is achieved, though I have asked. It seems obvious that air borne vibrations hitting a platter or tonearm can not be addressed by an active isolation device and be attenuated before they have done their damage to the sonics of the system.

Jarek, could you go into some detail about how active and passive devices differ when placed below audio components which generate their own vibrations, and more specifically, how one type or the other may be more effective for suspended turntables or non suspended turntables?

 

[PeterA]

No specs or measurements yet, I'm in the early stages of comms w the guys at Stacore and will ask them to post
They are happy to allow the platform to be placed direct on the floor to situate the tt at low level
Fwiw, when I auditioned the active Accurion i4 some yrs back, the sales manager was happy to pop that on the flr in my apartment
The way I see it is if these devices are overengineered to isolate comprehensively, there should be no reason they shouldn't be able to be used on the flr

Perhaps not, but from a convenience point of view, have you tried cleaning a stylus, placing an LP on the platter, or adjusting VTA while crouching down on the floor? I prefer my turntable up fairly high so that I can easily see and adjust things. Lighting is also important. However, if it a turntable is placed too high, and it is very heavy, then one risks lateral instability with some poorly designed racks. I find the ideal location is at a comfortable height on a sturdy/rigid rack off near a side wall, far in front of the plane of the speakers, and not at a reflection point, avoiding corner placement.

 

[PeterA]

Marc, the measurements we have taken so far are not in the usual form you see at the lab platforms manufacturers so we decide not to publish them
to avoid misinterpretations. The measurement setup did not allow for that form of the transfer curve. We plan to repeat them in another lab
somewhere in the near future and have the data in more easily understandable format to be able to publish them.
But what I can say is that we do not do 2Hz or lower, nor we feel we have to as we are not designing a microscope platform.
Our resonant points on both platforms are about 4.5Hz unloaded, down to 2.7Hz (IIRC) fully loaded, multiply that by 1.4 to get the lower end of
the isolation region. Lab manufacturers pages are full of data (averaged; real life curves do not look so pretty) because those data matter in the lab.
The figure of merit there is the resonant point, the lower the better. This resembles the "ultra low THD" mania we
are all old enough (I guess ) to remember and all those discussions of 0.0001% vs 0.0000001% which had nothing to do with the sound.
Same here-one fres point or even the transfer curve will tell you nothing about the sound. I would try to avoid making
ad hoc correlations between some more or less abstract parameter and sound.

Hi Jarek, I understand this point of view. Could you tell us roughly the range of frequencies that are addressed by your devices? I just looked up your website and saw two photographs which prompt me to ask to questions:

1. What is the purpose of the three roller bearings separating the top of the platform from what looks like a preloading ballast plate in the "Advanced" model? Is this for a more stable, self leveling (three points) interface between the two flat surfaces and for some lateral forces effect?

2. I saw an image of a suspended Avid turntable sitting on one of your platforms, but the motor control unit was off to the side sitting on the top shelf of the equipment rack. Have you experimented with placing such a control unit/power supply up on the isolation device next to the turntable? Years ago when I had an unsuspended SME Model 10 turntable, I tried it both ways, and preferred the control unit up on isolation. This is what prompted me to order an extra large ballast plate for my current SME turntable. It has a larger footprint, and I wanted to accommodate the control unit next to it. Results are excellent.

 

[spiritofmusic]

Peter, Jarek can correct me if I'm wrong, but it looks like they're not trying to go for sub 1-2Hz isoln like Herzan et al claim
It seems that a fully loaded Stacore damps to a resonant freq of 4Hz, no lower
No, rather they're claiming Herzan etc by not addressing broadband higher freqs c100Hz are not as ideal for audio, tts esp, and by Stacore isolating/dealing with this noise, they are better suited to manage audio gear
And it's true, the Herzan literature, and Mike L's etc championing of the active approach are always talking about sub 2Hz, and never 100Hz+

 

[Stacore]

Peter,

Thank you for your questions.
1) Suspended and non suspended and platform types. I have no direct experience with active platforms so I speak from a purely theoretical point of view. In my view for a suspended tt an active platform looks like a safe bet as it is (or should be) inherently non-resonant. Stacking resonant (e.g elastomer plus pneumatic) suspensions with similar stiffness may cause troubles and unpredictable results. We actually discourage to use our platforms with suspended devices as a rule to avoid troubles. But this general warning doesnt mean two suspensions cannot work. In pneumatic platforms like Vibraplanes or ours one can controll the stiffness by the pressure and thus may separate the resonance points and make stacked suspensions cooperate.

2) This brings to the Avid. We tested it especially to see what can go wrong with stacked suspensions and how we can hear it. Unfortunstely for us nothing went wrong in that setup The suspensions worked ok although the effect of cleaning the vibration was not so pronounced. No,we did not think.of placing the PS on the platform. Thanks for pointing that.

3) The rollers and an additional plate in Advanced is a second isolation stage. The pneumatics are good allaround but their isolation in the lateral plane is not as good as in the other directions. The second stage on rollers "cleans" what is left after the 1st stage. Its resonant point is at some 1.6Hz,far enough from the pneumatics not to go oscillating.

 

[spiritofmusic]

Peter, the more I look at the Stacore, the more I consider it to be a modern up to date aesthetically excellent all in one version of yr Vibraplane/steel plate/ballast solution
If I'm not mistaken, you've been uniformly happy w what it's brought to yr SME, and this fills me w confidence a similar trick could be wrought by the Stacore on my tt
It's definitely in pole position re my investigations on passive isolation of my unsuspended rim drive

 

[Stacore]

Peter, I've overlooked

4) FR: we start effectively isolating at 5-7Hz (depending on the load) and I estimate we go up into several kHz,
addressed by a carefully engineered enclosure with acoustically inert materials (whose resonances we control well).

 

[Ron Resnick]

. . .

I strongly discourage to stack similar stiffness suspensions working in the same direction (e.g. vertical). The suspensions may go into beat oscillations (if their resonant points are close), with actually increased ULF vibrations instead of decreased.

Dear Jarek,

Thank you for writing to us here.

1) What would be examples of stacking similar stiffness suspensions?

Does this mean not placing a component with rubber feet on a table top which itself has rubber feet on which it sits on a rack?

Does it mean not using several mechanical "diode" grounding components in a vertical system? (For example, a table top on cones (Tiptoes) where the points face down to mechanically connect the corners of the table top to the top of the legs of a rack, and where the rack itself is on spikes to "ground" the whole system to a concrete slab?)

2) Do you believe vibration control techniques should be mixed, meaning, for example, having a heavy, solid rack the feet of which are spikes, but then having Sorbothane or some other vibration-absorbing material between the top of the rack and the table top which sits on the top of the rack?

3) The active isolation Herzan claims to work up to 1,000 Hz. Herzan suggests using a visco-elastic layer below the active isolation platform to handle vibrations above 1,000 Hz. (This remains extremely puzzling to me because I always thought there should never be any squishy rubber-type material below the active isolation platform.)

4) I am still not clear on why your product is better for audio components than an active isolation platform like Herzan.

5) What do you think of sophisticated rack and shelf systems such as Critical Mass Systems or Harmonic Resolution Systems whose products utilize, among other techniques, constrained damping layer shelves to reduce vibration by coverting vibrations into heat?