Speaker support
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.
Hifi Shelving
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.