Active isolation; what can it do for music reproduction?


i was involved in a thread about stylus drag on turntables where my use of active isolation came up. it was asked for me to discuss my views and use of this approach for system optimization. i mentioned it likely needed it's own thread to do justice to the topic. here it is.

excuse me if i get too basic here to begin with. i've not seen this subject discussed in depth on Audiogon before.

active isolation devices use piezoelectric sensors in 6 axis to sense resonance and piezoelectric actuators in 6 axis to compensate for that resonance. in essence it's a feedback loop of read and compensate. 

http://en.wikipedia.org/wiki/Piezoelectric_sensor

passive devices are more or less springs to one degree or another. springs float, settle and overshoot. active devices are relatively stiff; 500 times stiffer than passive since they can STOP and START. passive can't stop and start. you do see passive devices with automatic leveling, but otherwise they can only act passively as a spring. 

an example of an active device; the Herzan TS Series;

http://www.herzan.com/products/active-vibration-control/ts-series.html

the limitations of active devices are mainly as follows; 

---they are only really effective under 200hz.
---in stock form they typically have signal path corrupting switch mode power supplies.
---to be effective they need a solid base. which means a solid rack grounded to a solid concrete floor. suspended wood floors, or non-solid racks are going to compromise the performance.
---the gear being isolated cannot have it's own self resonance that might excite the active sensors. and not every piece of gear will benefit from active isolation. so active is very system context dependent. you can't just use it anywhere and expect a particular result.

there are very very good passive devices that approach what an active device can do; the Minus K, Stacore platforms, and Vibraplance are three popular examples. i'd recommend investigating these before considering any active devices. those examples do need the same solid floor and rack as active to be effective.

and another consideration is a passive isolation rack; the best example i can give is the Artesania decoupling rack systems. likely the best passive rack. again; a solid floor is going to allow the Artesania to perform at it's best.

finally; there is a website tutorial which can really get granular with deeper levels of information on active devices for those interested. 

http://www.herzan.com/resources/tutorials.html

lastly i will say that active devices are something you consider when you've mostly done everything else you can do and want to take things further. cross otherwise impossible thresholds of performance. you have a system that is where you want it to be. active is the bleeding edge. it will allow the music to escape the confines of resonance in a way nothing else can do. it's just physics.
mikelavigne
@mikelavigne   Thank you for this wonderful series of posts. Informative and educational and true to the spirit of our pursuit. 
And who says physics isn't fun?
Mike, you and others on this forum do so much to further the listening enjoyment of music lovers. Makes it quite the hobby.
Thanks Mike
This is interesting to me because I think I am at that point where I do not want to make big changes because what I have is doing really well for me. And one thing I did recently was put some passive isolation feet under my speakers. I was quite impressed with the nice overall improvement in textural detail, less smearing. Even though I could not hear anything wrong before. So I have just been thinking about isolation of my other components.
Very thorough background on the offerings, use, and effects.  I have used two large Herzan tables since 2010 to support my TT, DAC, and preamp. In general I would agree completely with your notes about sonic impacts.  When I added them to my system I was very pleased at the improvement they wrought to my SOTA Cosmos table at the time. It seemed to strip out colorations at several frequency regions, not just below 200 hz.

The Herzan units incorporate the active pezioelectric system from 200 hz down, but they also employ a mass and spring passive element that is effective, too, and certainly above 200 hz.  

Regarding the switching power supplies, I simply run them on their own separate electrical line, and I have not been able to detect any detrimental sonic impact from them. It would be interesting to toggle some lps’s to see if I can hear a difference...

The Herzan units have a bank of LED lights that flash when the sensors are stimulated across their threshholds, and another bank that flash when the canceling actuators fire to cancel the detected vibration.  IME these actually fire pretty infrequently, and require a lot of system volume to do so.  This leads me to believe that the greatest impact I am hearing is from the passive element.

So, fun story that illustrates their effectiveness: I bought mine dirt cheap from a Silicon Valley salvage firm that was clearly parting out some failed venture, and they had them poorly described on eBay. I had to ship them 1500 miles, and they looked a bit worn when I got them, so I was worried that they may not even work. To test them, I set them up on some steel tables we had in our Lab where I work, and plugged them in. They lit up! Then I set a cup of water on each and a cup of water on the steel table surface. I pounded increasingly vigorously on the steel table and my tympani rolling did not create so much as a ripple on the surface of the water in the isolated cups, while water was jumping out of the cup on the steel table. I was a true believer at that point! Active vibration isolation is dramatically effective. Probably why these are favored for supporting scanning electron microscopes.
What's interesting about active anti-vibration is how the electrical quality of the power supply affects the performance for audio applications.

Unlike optical applications, residual noise in audio applications needs to separated into noise correlated with the music, and uncorrelated.  Correlated noise has a lot more effect than uncorrelated and needs to be carefully managed

Taiko Audio in Holland experimented extensively and developed a linear power supply housed in Panzerholz which utilizes high end audiophile power supply practices