I posed the following a couple of years ago, but no-one offered any answers...
It seems to have become common practice with equipment racks to have the rack shelf, then an additional shelf/board on top of it, on point contacts (domes etc), with the equipment sitting on that, while the equipment commonly has some form of elastomeric feet of its own.
Can anyone explain the logic of the extra board, and how it supposedly improves sound quality?
I ask because it seems to me that the extra board will create an additional 'sounding board' that will be excited by incident sound, causing vibrations at the board's resonant frequencies and thus potentially degrading sound quality unless the equipment feet provide adequate damping isolation or damping (in which case why bother in the first place?)
Surely a better approach would be either:
i) At the very least make the second shelf/board heavily damped (e.g. by adherent damping pads or coating along the lines of 'dedshete').
Ii) Rather than an extra shelf/board near to the size of a rack shelf, use small plates (whether glass, stone wood, round, square or triangular) just 2-3 inches across, under each equipment foot, each positioned on three point contacts (rather like drinks 'coasters' but made of something substantial). This would provide a much smaller surface area for aural excitation, while pushing the resonant frequencies much higher, where sound energy to excite is likely to be less and equipment feet might be more effective at absorbing.
iii) Have the main rack main shelves themselves decoupled from the rack frame by point contacts, and the shelves damped, whether by the intricate routed channels some use or by applied damping material (or both), negating the apparent need for a second decoupled shelf/board to do the same. This is down to rack design - and I think some may indeed be like that.
iv) Have the rack dispense with conventional shelves entirely, instead having support bars or projections just adequately sized to take small isolation plates as in ii) - though that would require either a customised rack for each installation or standardisation of feet positions on all equipment, so would be likely to be either very costly or dedicated to a single equipment brand (such as Naim...)
i) and ii) could be simple, low cost DIY upgrades.