Originally Posted by PleasantSounds
If I remember correctly, the rack was the Quadraspire Sunoko Vent T: non-rectangular shelves with wood finish but most likely MDF based, solid aluminum columns, spiked feet.
The CD player was the CD5 by Audio Research, connected to AR DSi200 and playing through Cremona M speakers. The CD5 DAC has been used (xlr connection to the amp).
Regarding the impact I have heard, I could describe it as sounding somewhat veiled and less engaging in comparison, when based on "normal" table. The base has been swapped several times back and forth and the impression was consistently the same, with several music samples.
Thanks for the details. I looked at the Quadraspire site and saw their shelving system.
What I was looking for was some way in which their rack would create a mechanical low pass filter tuned for cut-off below the audio band. This can be done by adding mass and placing a resilient decoupling mechanism between it and the source of vibration. When I look at the rack I don't see any resilient decoupling or added mass. I see they've increased the tension in the joints and placed spiked feet on the legs, both of which would actually increase vibration coupling to the floor. The MDF material is not reinforced, which I would have expected in order to tune the diaphragm each shelf creates to a higher frequency. And of course the entire thing is open to air, so any airborne vibration coupling to components is unaffected.
To isolate something from the vibration generated by a sound system the method of vibration coupling has to be determined. In this case, there are two paths. One is through the air itself, and the other is coupling from the floor, which carries vibration physically coupled from the speakers as well as vibration the floor itself picks up, acting as a diaphragm, from the air. The floor is physically coupled to components from table or rack legs and supports and then the shelves. So a more isolated rack would be an air-tight box made of several layers of massive material, each layer isolated from the other through resilient couplings adjusted so that the mass of the innermost rack and the couplings create a mechanical high pass filter tuned well below audio frequencies. The air tight box would effectively prevent air coupling, and the isolation system would reduce floor coupling. Considering all of that, it would make more sense to put the components in another room and work on resilient mounts to decouple a standard rack from the floor. The results of all of this are easily measured and confirmed with an accelerometer placed on each component in various locations.
Physically moving a component within a room completely changes the coupled vibrations, and not to a small extent. Bass modal distribution, especially without multiple bass transducers, can be very spotty, and just moving away from the mid-band sound source can reduce the airborne vibration by several dB. You don't have to change the rack to achieve that.
I'm not certain what you heard, but I'm pretty sure it wasn't because the rack was changed.