Richardkrebs,
I imagine its possible to define an object into existence to suit ones argument
.but Im not sure where it gets you?
To define a plinth as a shelf allows for a rack, a platform and of course the floor to also comply with that definition.
It gives us the situation where audio items like power conditioners and DACs and SUTs and preamps and amps are all on plinths?
And for those with a REAL turntable plinth on a Minus K stand on a shelf on a rack on a floor
..we have a plinth on a plinth on a plinth on a plinth
..?
It would also seem logical that different shelf materials, size, shape, support method, spikes, et el would make a difference.
This would only be logical if one could conclusively prove that there was stored energy within the shelf or within the object ON the shelf which REACTED to the materials, size, shape, support method, spikes, et al in a way that affected the motor, bearing, platter, record, stylus, cartridge and arm in a turntable system for example?
Despite the availability of accelerometers and other devices designed to measure and quantify vibrational energy and its transfer within materials
..I have seen no scientific evidence to support the many statements made by audiophiles on the nature of vibration draining in regards to turntables
.and any quantification of such?
The vast majority of audio systems are supported on the floor of the listening room albeit on racks or stands of some sort.
The vast majority of those floors are suspended timber frame or suspended concrete slab
..very few are concrete slab-on-ground.
All suspended floors (be they timber, steel or concrete) are under bending stresses of various magnitudes which create low frequency acoustic energy within the structure.
This low frequency energy (often resulting in movement) is transferred to the rack/stand/shelf supporting the equipment and results in higher frequency energy transmission and movement which is passed through to the equipment supported thereon.
With all this low frequency energy swamping the stands, racks and shelves
it is no wonder that differing methods of support and differing materials all have an effect on the transmission and damping characteristics?
But you are mistaken to assume that those who have absolutely no structure-borne feedback will also experience the same phenomena.
My floor is a reinforced concrete slab-on-ground topped with polished granite and is totally bereft of any structure-borne sound.
My turntables sit on a stressed-skin MDF shelf cantilevered from a masonry structural wall supported on that reinforced concrete slab.
The turntables sound identical whether they are sitting directly on the polished granite floor or up on the cantilevered shelf.
I have tested many methods of support for the turntables including an additional independent shelf on top of the cantilevered one
.sorbothane feet, Delcrin footers, Stillpoint Ceramic feet, Stillpoint Ultra Minis, ceramic cones, aluminium cones, steel cones, plastic cones, brass spikes, steel spikes and stainless steel spikes. I have placed various materials between cones/spikes and the supporting shelf including metal coins, plastic, cardboard etc
and with all and every variation
..there has been zero change to the sound.
When there are no Structure-Borne feedback problems
there is nothing to affect the turntable adversely (other than Air-Borne feedback
..but that is another can of worms).
In fact a sure way to determine whether your room suffers from Structure-Borne Feedback is to see if changing the spikes, rack, footers etc results in an audible change?
But back to the plinth
Im sure you have much to contribute to a discussion on a real plinth into which a turntable like a DD or Idler may be mounted? :-)