Isolation Advice Needed

I'd suggest a number of concrete piers to support the floor. If your builder can't or won't do it, you could add hydraulic jacks. Suspended floors bounce. 

Black Ravioli are made in Scotland and not well known in the USA.

Very well priced at approx US$260 for a set of four.

Will I get them back? Hope so. He also has one of my grounding boxes, and my Audience AU24Sx RCAs. 

Mechanical jacks under the floor are a cheap, stable option but will not solve the real problems of your stereo. You can effectively build a suspended floor under you speakers with the speakers mounted on springs and the suspended floor further mounted on springs and then the wooden floor.  Mine are blocks of laminated pine, built like mini butcher's blocks, 600mm x 450mm x 100mm. this arrangement isolates the speakers from the floor and the speakers from each other. Spring rates depend on the weight of the speakers for the first set of springs and the weight of the speakers and blocks combined for the second set of springs. Depression of each set should be around 25 - 35 %.  This is achieved by reducing or increasing the spring size and or number of springs. Nobsound springs are good but more expensive than others on Amazon. Total cost for my set up was approx $120.

I also have wood floor over crawl space. It is springy, has been problematic, luckily solved now. It was built in 1951, I think with ’green’ wood (not properly dried) as so much building occurred after WWII. More problematic than most suspended wood floors.

My Thoren’s TD124 Magnificent, but it’s Bearing was very susceptible to vertical motion, traded it for that reason, still miss it.

My Audio Technica AT120, much lighter player, was ok but cautious steps when close. No dancing or kids running nearby please.

Current JVC Victor Heavy TT81 player in a heavy CL-P2 plinth was similarly ’cautious approach’ until I put it on 2" x 2" isolators, they can be seen in 7th photo here.

I have since wrapped the blue with black tape, far less noticable

.....................................................

A major part of my problem/solution is: the floor slopes immediately from the wall, the front of the rack is 3/4" down. Then the floor levels out.

Previously I had little blocks under the rack’s ends which were recessed from the front a good bit. Then I would level the Turntable on the top shelf. I realized, all the weight, rack, 80 lb amps, two double wide shelves of equipment was tilted forward, much of it in front of the recessed end panels, thus any vibration involved ALL that weight forward of a fulcrum point.

I built new side supports, tapered as needed for 3/4" extra in the front, and extending a few inches in front of the rack, (also seen in the same 7th photo) so the entire rack and equipment is level on that sloping floor, all the weight now behind the front fulcrum point.

Each glass shelf has it’s own firm rubber isolators, and top equipment is on racks I designed with firm rubber feet.