Audio Rack Selection

One of the best racks I've ever had was a tall, thin rack with a 70kg turntable on top. The trick was simple: the rack was extremely rigid with plywood skirts (glued and screwed) on three sides, and fixed to the wall studs with 4" long #12 screws.

Not sure whether it was a reinforced shelf, a permanently fixed rack or a wall extension, but damn if wasn't stable. Performed nearly as well as my long, low, slate-topped, structural post-fixed on two sides, wall-fixed  plywood cabinet, joined to concrete.

Just constrained layer damping, nonoise. That, and an irregular shape.

Some few materials have constrained layer damping built in, like Panzerholz, or, to a lesser extent, slate, or Baltic birch plywood. The trick is to put two materials with different speeds of sound, in intimate contact, like hardwood and elastomeric glue. I used 2 1/2" of Baltic birch in three layers, bonded with elastomeric glue, bonded to a topping consisting of an inch of slate. Slate itself consists of very thin layers of rock, which reduce sound transmission and resonance.

The very best shelve material is Panzerholz, which I used in the plinth of my DIY turntable. So I have three different non-resonant materials, with different properties, which prevent resonance.