Rack Stack Vibration Isolation advice

you want that rack perfectly level, now, and forever, no matter what is placed where within, so I would not put anything that compresses below the main floor contact.

I bolted new end hardwood legs onto my rack, to get the fulcrum points in front of and behind the weight, tapered because the floor is slanted, shims for final leveling, I could have made them taller as you need.

It is hard to see, but each glass shelf is isolated from the bentwood frame below it on hard rubber spacers

the JVC Victor Plinth’s feet are isolators and adjustable for leveling it, however my wood floor is flexible, my final solution was rubber/cork below the TT’s feet, after they worked, I wrapped them in black tape.

there is a lot of weight, but because the rack is level, it doesn’t move like it used to.

rather than a wide rack, I like separately movable units, my preamp and amp unit has felt feet and slides easily enough, R2R tape is on a separate movable unit left end

and I made a stand/surround so I can move the bottom preamp without moving the heavier amp above

wide open back for access and ventilation

@whyrichard 

I have used very inexpensive Sorbothane hemispheres between two flat surfaces supporting a total load of about 70-kg or 150-lbs.  For that load I needed eight 50-mm hemispheres.  The calculation is not trivial but Sorbothane’s website has a very detailed Standard Product Guide at Sorbothane-SPG.pdf.  They are also very helpful if you email them.  Total cost was under A$100.

I also have IsoAccoustics OREA Bordeaux which are about that price each (ouch). I would not use IsoAccoustics loudspeaker isolators for a rack because they are designed to allow sideways movement but not back-and-forwards.

@whyrichard Sorry, let me give you more detail.  Consider a layered isolation platform, like a big Dagwood sandwich.  (I'm assuming you remember the old Dagwood comic strip - google it if you need a photo).  There is sliced bread, a layer of mayo, then a layer of cheese, a layer of meat, a layer of lettuce, a layer of tomato, a layer of a different cheese, etc. until you get to the final layer of mustard and sliced bread. 

A layered isolation platform is just like that.  If you have a layer of wood, then a thick layer of felt followed by another layer of wood - you can see the different densities of felt vs. wood.  Just to make the numbers nice, if there is a density ratio of wood to felt of 1000:1, then vibrations will attenuate about that same amount.  

Note that wood has different densities, consider balsa wood versus iron wood.  You can use thick carpet instead of felt and use cinder blocks instead of wood (we will ignore cosmetics for now).  The point is a few layers of dense material and low density material will really knock out vibrations coming up from below.  Note that this doesn't kill airborne vibrations impacting the equipment directly.  

Also, look at what the floor is made from.  In my house, the floor is concrete, so I am not too worried about floor vibrations.  In college, my roommates and I rented an old, pre-WW2 house with weak wooden floors.  I think a cat could run across the floor can cause the BSR tonearm to bounce.  We put three layers of carpet, a cinder block, another three layers of carpet, another cinder block, three layers of carpet, and then the table upon which the turntable sat.  That cured the problem completely.  We could jump on the floor, and it wouldn't skip - I know, we did that to test it.  That is a very good test, BTW!

Some of the posters mentioned the spring isolators on Amazon; yes, they will work in place of the low density material.  When purchasing isolation items, look for the weight rating for which they are designed.  If something is designed for 10 to 50 pounds, then isolating something weighing 30 pounds is about optimum.  Likewise, if something is designed to isolate 100 to 300 pounds, then using it to isolate 30 lbs will not be very effective, if at all.

The better isolators have graphs showing the attenuation ratios for a given weight range.  Yeah, they cost more because they did all the testing, but if in doubt, look at the graphs and choose the optimum isolator.  Avoid buying any isolator that doesn't specify it optimum weight range.  It might be okay, but you won't know until you spent the money and tried it.

Let me know if you need more info than this.

R

That is a fantastic and clear explanation. Thank you. 
 

I think I intuitively understood this by alternating soft (felt, Sorbithane, neoprene) with hard and heavy (marble). 
 

with my outboard crossovers, I have them on the floor behind my pure audio projects. Their sound isolation is currently: sandbag —> stone block —> light weight wood (mainly for mounting the crossover and controlling cables) 

think this does the trick? Could be improved? 
 

https://www.dropbox.com/scl/fi/e84ep6reubm9rknps6cgn/IMG_7054.jpeg?rlkey=8eo1diz7u5rfzazkk9pttfhbu&st=q68s9rph&dl=0

@elliottbnewcombjr 

That is an amazing integration of electronics with vintage / wood / stuff. It almost makes the cold boxes for electronics disappear.