I've owned a high performance decoupling rack system, the Grand Prix Audio Monaco with the Formula Carbon Fiber shelves and Apex footers. for this rack the normal approach was either the stock footers directly on the shelf or some sort of solid interface between the bottom of the gear and the shelf (BDR cones seemed to work well). typically you would not use a decoupling footer + the GPA Monaco full blown system.
the idea being combining multiple decoupling products has unpredictable results; the GPA approach being a soup to nuts 'system'. more typical is either decoupling footers with a solid rack, or solid footers with a decoupling rack.
both approaches intend to do the same thing.....remove resonance feedback from the floor, lower noise, improve musical focus, leading edge definition, and bass articulation.. some rack systems 'claim' to deal with acoustic feedback too. one additional benefit of the most spendy racks system is aesthetics for sure, they can be beautiful. footers are best heard and not seen.
I prefer the greater customization ability of the decoupling footers.....although in the case of the GPA, you did use sorbothane pads of varying thicknesses to tune each shelf to the weight of the gear on the shelf. then every 6 months you replaced the pads as they fatigued (a royal PITA).
however; you also have turntable situations where you might use some sort of mass 'sink' (maybe sand or lead-shot filled or slab of steel) as an impedance layer below decoupling footers and the turntable. so mass is another factor.
most of the well known decoupling racks do recommend you place the gear with stock footers on their engineered shelves directly.
ignoring active isolation my personal choice is for a cheap solid rack and high quality decoupling footers. this is a cost effective approach. top level decoupling racks are mostly very spendy......and once invested in one of those you are pretty much committed long term. I've been using my 8 sets of -4- Wave Kinetics A10 U8 footers for 7 years now all over my system and they have never let me down. I vary the number I use depending on the weight and they work.
I view any decoupling shelf not part of a branded rack system as like a footer, such as a vibraplane.......since you can place it on any rack.
maybe a 'Minus-K' or others like that are closer to 'active' than to footers.
Not on equipment racks as I always had a wall mounted shelf system, which was steel tube sand filled and stone shelves (not glass or MDF). Now, I have a heavy marble and stainless steel framed desk.
But on speakers I approached this with a budget conscious mind. And can I learn something from my mountain bike suspension system (rubber doughnuts)? There is a lot of snake oil in this stuff. In my view, it depends on what you want to achieve. Do you want to couple or uncouple? I can't imagine why anyone would want to couple, but that is my opinion. In the case of speakers for example, we have decoupling of the floor and reducing resonance in the cabinet. I tried various 'de-coupling feet' on loan, and though very pretty (and expensive) in the end I had some very heavy granite stands made, and sat the speakers on thick rubber 'doughnuts'. This killed any vibrations from the speaker connecting and exciting the floor. It also had the extra effect of reducing vibration in the speaker cabinet base itself much as how my mountain bike suspension works. The bike and me is the speaker, and the floor is the ground. A way has to be found to decouple the bike from the floor and kill very quickly any vibration. To do that requires more than one type of material and converting it to heat. That and negate the continuation of that movement (see-saw). I thought what I need is a combo of mass, and movement to absorb that energy. Any kind of solid footer that has limited or no absorption in my view will never work.
If you couple any vibrating element in any direct way, no matter how fancy of complicated the construction of that foot or base design, it will transfer that energy down to the next component or the floor. If the floor is of low mass and / or suspended as many wooden floor or even laminated floors, then that will cause havoc with sonics.
There has to be found a way to kill the vibration. The best way IMO is a combination of mass (weight and dense material) and absorption in the connection between the emitter (speaker) the the receiver (the floor).
Funny, I bought my current speakers used from a dealer for 8K, and later asked his advice on what footers to use. He suggested some Grand Prix Audio Apex at only 2K for 4! Hmm, that's 4k for a set for 2 speakers. Yeah right.... My granite stands cost me 500 USD, weigh about 50 kilos and the rubber doughnuts 25 USD from a car repair centre. I also put 2 x bands of neoprene tape on the floor under the granite bases. My floor is set into concrete, and at very high volumes on bass heavy material I get no vibration at all.
In my previous house, I was on a wooden floor and that did create different challenges. I actually wall mounted my (smaller) speakers for that house on stainless steel wall brackets I had made and were bolted into the stone walls. Then sat those speakers on the brackets on a layer of clear silicon. Again, I felt no vibration or interaction with the wall and those speakers. If you have floor standers on a wooden floor, then experiment with heavy stone plates and some form of decoupling like sorbethane or neoprene. I am not in favour of fancy turned aluminium feet with tiny layers of 'some other' material for a form of decoupling. It won't contain the energy in big speakers, impossible. Better going big a bold, mass and size to do that IMO.
The tricky part is getting the amount of absorption right for the setting and environment. Too much may reduce focus and damage the stereo image 9soggy effect). I think go cheap, and try various ideas. Best way IMO, and don't get sucked into 2K footers! Pic below of my Granite stands. The box sides are 4 sided granite with expanding foam infill. There is a 3cm gap between the base of the speakers and the top of the granite. They 'rock' slightly if I push the top of the speaker, within 2 seconds it goes back to dead still. Seems to work fine.
Not wanting to open this up much, but I would comment I don't believe in Glass shelving. Even laminated glass (3 panel laminated) is not acoustically dead. If any vibration happens in a shelving system, it will impact sensitive gear such as a CDP, DAC or Tube pre-amplifier. And a turntable even worse of course. I used granite shelving attached to the strong steel sand filled wall mounted system and absorbing feet under my gear (not coupled). Seemed to work ok, and again was cheap to do. A metal working shop can make them cheap to a scale drawing.
I've been having some very enjoyable private conversations over the last few months with Barry (Barry2013) regarding the effects of racking and more recently isolation. I am sure Barry can speak for himself but I also sure he and I have a similar take on the subject. They both make a potentially significant difference and I am not really certain you simply say one is going to be less (or more) important than the other. Thus the short answer in my view is that one needs both.
Barry's equipment and racking is vastly superior to mine, however we have both observed how a good rack is a critical foundation to what follows. To my way of thinking, it would be folly to audition footers without getting the racking sorted out first. Afterall, the racking serves a practical purpose of housing the equipment, so there are many logistical and practical issues to resolve when considering which racking systems might be suitable. Racks will definitely change the sound of a system (hopefully for the better), however unlike footers, one needs to factor in far more than just sound when selecting a rack. Therefore, one should purchase the best rack they can afford that serves the practical purposes of housing the system (and with a goal of good sound in mind), then move on to footers in order to fine-tune the sound.
Of course, there are racks and then there are racks - many of the higher end ones already have extensive (and expensive) isolation features built into them, however I'd suggest very few racks out there at any cost can do as good a job as a very good rack together dedicated, high quality, third-party, purpose-built footers.
I have likened footers to violin strings. There is no such thing as a perfect violin and there is no such thing as a perfect hifi component, let alone a perfect hifi system. The multifarious violin string products available today are used to fine-tune the sound of a violin, mitigate the instrument's weaknesses, play to the instrument's strengths and provide a consistent "feel" to the player. It is exactly the same with footers. I've been experimenting this last few weeks with admittedly budget solutions, but all of them had different strengths and weaknesses, though I thought it was somewhat ironic that the one with the greatest strengths and no obvious weaknesses at all was the cheapest solution I tried (Project "Damp-it" of all things!).
One won't even find terribly much agreement amongst the manufacturers of what footing methods work the best. There is a school that subscribes only to damping (using softer, compliant materials), then there is a school that subscribes to mechanical isolation and "drainage" (Symposium Rollerblocks, for example) and then there are solutions that might be regarded as hybrids, such as Wave Kinetics and the Townshend Seismic Pods. I am sure all of these solutions sound different. That said, it might be relatively easy to measure how well a footer performs, but since many can measure well yet all sound different, the only option is to choose a footer using a subjective listening process. A slightly worse performing footer by measurement may sound subjectively better because it's weaknesses counteract existing weaknesses in the system (which, in my view, start at the power station miles away and don't end until the sound wave hits your eardrum).
So for me - rack first, then audition as many footer solutions as possible. You might happily live with just a good rack, but I am convinced that no matter how good the equipment is, it will still benefit noticeably from a well-chosen footing system.