A couple of comments:
When I think of Target wall shelves, I'm thinking of their original design with the angled side braces. This "triangulated" design is a structurally braced shape, deriving its strength from its geometry.
The current Target design(s) use a "box" frame which is only as good as the welded connections, the shear strength of the weld itself, and the metal tubing's ability to resist bending. If I had to buy the current model, I'd take it to a welding shop and have some angle bracing installed on each side. Just look at Billy Bags designs -- every damn thing (except their little 2020 amp stand) has diagonal bracing.
Steel is the ONLY material for the BEST structural rigidity. Titanium and magnesium are better in the strength vs. weight department -- not an issue in audio (usually ;--)
A truly rigid connection between dissimilar materials is impossible because it will be mechanical, not monolithic like a weld. Further, mechanical connections almost always involve a third material like glue, or screws. This eventually leads to loosening of the joint, due to movement, structural stresses, thermal expansion, and variations in humidity. Anyone who thinks they can make truly RIGID structures out of any material that can't be welded is just nuts IMO; they are depending on intuition without knowing anything about physics and math. Intuition is useless, even when you get a lucky break, because you can't go back and figure out why it worked! (Simply PLACING a wood, corian, acrylic, granite, etc. shelf on some kind of rigid steel frame is not what I'm discussing here.)
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Acoustic isolation of a TT or other object from airborne sound (pressure waves) is another fantasy. Oh yes, sonic pressure waves do indeed exist, but they exist in a gas (air) which means they propagate in all directions -- unless you are literally on top of the source. And they exert the same pressure on all surfaces of an object, if that object is fully inside the space where the sound occurs. Floors and walls are a different story. When they vibrate, it's because the pressure on the other side is different; usually lower.
So if a TT is "dancing to the music" it's because the structure that it rests upon, (along with everything ELSE one has contrived to stick under it,) is all already resting on a moving platform: the floor!
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