I’m trying to remember the name of our friend from Japan.
I’m sure that having experienced more than one earthquake, he will assure us that concrete floors can indeed transmit vibration! 
(BTW, although it doesn’t really matter I’m Mme rather than Mlle!)
Mme is not Miss in English ?
I suspect you are joking about earthquakes…I was more referring to vibrations from the loudspeakers going into concrete floor.
Mme is Mrs
Mlle is Miss
No I wasn’t joking about the earthquakes!
And I’ve just found the member to whom I was referring it’s @feeling_zen.
The same nature of concrete that transmits (and can amplify the vibrational excursions of earthquakes leading to structural failures in buildings) can also play a part at audio frequencies in transmitting footfalls or even vibration from speakers. In some cases concrete floors (specifically suspended concrete floors with concrete or steel beams) can be quite resonant.
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Incidentally I also understand the French cultural use of Mlle when addressing a woman in her 50’s or older… quite a minefield in the days of internet communication when the non-verbal clues aren’t available either for age or for understanding of intent! 
In any case my intention was to write Mme, so Mrs. I hope I haven’t hurt you.
In France the use of Mlle, Mademoiselle, is not used anymore. But personally I continue to use it in some circumstances.
As for transmitting of vibrations through concrete, thanks for clarifying. So I guess some decoupling between a rack, like in the picture above, and the floor, should be worthwhile I feel.
No hurt taken at all; and from my observation when in France, the French as a nation do excel at politeness, so you need not worry at all.
I agree, dependent on the nature of the floor, if it is suspended, some decoupling may be beneficial, particularly if a heavy plinth is used direct coupled to the rack, and that plinth is then elastically decoupled from the floor. If however the concrete is a concrete screed laid directly on an earthen base (or hard core etc.), then no decoupling will be necessary.
Of course, but those vibrations won´t be transferred to any cable nor introduced into any signal carried by a cable. Just visit a bridge, stand under it and listen to the cars crossing it - it´s princciple is equal to quite similar 
In that case, why bother on an audiophile rack like a Fraim if someone has a concrete floor ?
I cannot find an online reference but recall that National Geographic magazine showed that it was impossible to mount a camera completely vibration free on a tripod. They went so far as to mount fixings into bedrock and still had blurred images.
Then as Xanthe mentions concrete beams can resonate, I was at work when the council was replacing the footpath outside. It was total excavation and the hardcore infill was compacted using a vibrator plate about a metre square under a trailer with a massive diesel motor. Keyboards, cups etc waltzed across desks.
Optics always sounds better than physics and believing beats wisdom all the time 
I think so too, although the glass platforms are already (mostly) decoupled. So decoupling the unit from the floor is presumably just to further minimising the transmission of vibration.
I’m in Christchurch, NZ and we’re not short of earthquakes here, either! Our house sits on a bedrock hill.
There is a UK manufacturer who builds isolating devices and discusses the impact of background vibration, including from earthquakes. It seems reasonable to me that it’s worth isolating from this.
I imagine that the mass of the unit will help to dampen background vibration? Especially with loads of LPs.
Our local university has their earthquake measuring equipment deep within the hill in a disused tunnel, to isolate it from traffic and other background vibration.
Earthquakes or just that, easy to observe the transmission of vibrations through the concrete.
The problem also in your rack is that the spikes are not very heavy, so the vibrations from the floor can reach the shelves, even if the components are under glass.
At least it’s what I feel.
Does the mass of the spikes make a difference - how is that so?
Thanks FR I appreciate your opinions.
Consider each mechanical interface individually (not totally valid, but analysis of the interaction between different components joined by multiple interfaces is WAY outside the scope of this thread).
There is a mass and a vibration source on each side; this represents an energy source and an impedance (both of which are frequency dependent). The interface creates storage/compliance and loss moduli (think mass/springs and dampers) connecting these energy sources (again both of which are frequency dependent), and reflections (also frequency dependent).
The rack sitting on the spikes is one mass, the floor is another mass, the elasticity of the tip of spikes and the tiny amount of the concrete on which it sits are the compliance (steel had a low loss modulus). Increasing the compliance (i.e. using springs) will reduce transmitted vibration at some frequencies, but make it worse at others. This is what you are trying to control.
Me in Vienna too, but I don´t listen to music during an earthquake. 
It seems to me that using scientific reasoning, even mathematical calculations of resonant frequencies, can lead to the construction of prototypes. These prototypes can then be used for further development…because all of our contexts are so different. No earthquakes here in the Forest of Dean! Be prepared to experiment!
To do the analysis to the level required to be a well justified basis for a theoretical design for an audio rack with the goal of specifically defined control of vibration would require dynamic finite element analysis.
By no means an impossible task, but I certainly don’t have the necessary software (or the inclination to take the time required for such an exercise ).
…and that’s before you even start constructing/ manufacturing the components!
If your rack sits on a needle , like a thick and tiny spike, it will be less decoupled from the floor vs a big and solid spike.
I had tiny spikes on my speakers when bought them. I replaced them by bigger spikes later. The sound improved. I hope you understand what I try to say.
Yes I think I understand.
I think you are saying that the spike benefits from a big contact surface area with the unit. Is that right?
Yes, a bit like the spikes under the Fraim.
