Racquetball isolation platform perfection

good discussion guys & perfect timing for me! :-) I am in the midst of making a tweak to my TT isolation platform! I've had a sandbox with a "floating" top-plate under TT for the last many yrs but recently felt (after reading some threads on another forum) that I could do even better.
I'm now thinking of isolating the rack shelf from the rack using 3 brass cones. Then, isolating the sandbox from the shelf using another set of 3 brass cones & finally isolating the "floating" top-plate from the sand in the sandbox using large bubbles bubble-wrap.
What do you guys think??

I was also thinking of racquetballs & squashballs - I felt that the racquetballs would be too bouncy hence might not be effective in damping but I'm happy to read from Timtim that they convert all kinetic energy to heat. Timtim, can you please provide the link to that article? thanx!

04-21-09: Emorrisiv
I was thinking of doing the same thing but was thinking hand balls or squash balls since they are much denser than raquetballs.

I *think* that in this case denser would be worse, no? The denser the material, the higher the coupling & the worse the isolation. Racquetballs might be better as they are more full of air - less coupling??

This is fun.

"I *think* that in this case denser would be worse, no? The denser the material, the higher the coupling & the worse the isolation. Racquetballs might be better as they are more full of air - less coupling??"

Could be. I would never claim to be a expert on this subject. Happily it is cheap and easy to experiment with any of these balls, since they all have virtually the same OD and should fit the DIY cloud platform.

Keep the conversation coming.I for one can't learn enough about the couple/Decoupling topic and the hobby in general.

e

Keep the conversation coming.I for one can't learn enough about the couple/Decoupling topic and the hobby in general.

OK! :-)
here goes:-
last night I did an isolation test (the idea was provided by a vinyl-phile from overseas) wherein I switched on my electronics, set the volume to that level I normally listen to, put a LP that I did not care about on the platter & set the stylus onto that LP. NOTE: the TT motor was NOT spinning. I did not want the platter spinning; all I wanted was the system to be 'live' i.e. the stylus to be in "picking up" mode.
Then, I started an extensive knuckle rapping test - rapped on the rack, rapped on the shelf the TT was on, rapped on the plinth, rapped on the motor, rapped on the LP far away from the stylus, rapped on the LP very close to the stylus.
Each time I rapped, I listen to the output from the speakers - could I hear the my knuckles rapping thru the speaker outputs?
Yes, I could when I rapped on the sandbox on which the TT sat, on the plinth & on the LP. :-(
The volume was not loud at all & the freq was on the low side. I did not have a SpecAn or a o'scope but I'm *guessing* that the freq was in the 100-200Hz range.
I got some more isolation work to do......

Bombaywalla,
Can you provide any scientific study or evidence, any physical or acoustic principles or formulae which correlates the 'knuckle rapping test' with the behaviour of 'real-world' acoustical feedback?
I see many audiophiles who place great importance on this dubious 'test' and have seen no evidence of its relevance in scientific terms?

04-22-09: Halcro
Bombaywalla,
Can you provide any scientific study or evidence, any physical or acoustic principles or formulae which correlates the 'knuckle rapping test' with the behaviour of 'real-world' acoustical feedback?

I don't have any evidence at the time of writing this post so you are free to dis-regard my post re. the knuckle rapping test & carry on w/ your life.
I'm afraid that I do not have scientific evidence, etc for every tweak that I do. If I were a man who did every tweak only after I found scientific evidence I would most likely not be in this hobby. Many things that we obsess on in audio have not or cannot (due to our inability to measure the exact parameter) be explained. And, of course, there are many other things in audio that do have a scientific background.
So, if you are the kind of person who wants evidence before even considering a tweak, then, the test I suggested is not for you.
My rational for the test was that knuckle rapping manually & forcibly excited the resonances in the rack, shelf, sandbox, plinth, platter. These resonances could very possibly be excited during the course of vinyl playback, couple to the TT, be picked up by the sensitive cartridge & be heard thru the louspeaker. I do not know how loud the music would have to get or how much vibration would have to couple into the rack for these resonances to be excited but, intuitively, the harder one would have to rap on the rack/shelf/plinth/sandbox the louder the music would have to be for the resonances to be excited & for them to be coupled to the cartridge & heard thru the loudspeakers. Again, intuitively, harder the knuckle rapping in order to hear it thru the loudspeaker, the better the TT isolation. The goal is to get to the point where none of the knuckle rapping is heard thru the loudspeaker & apparently, from talking to a few people, this is possible.
From the viewpoint of available commercial TT products, I can see this in the implementation of the top-of-the-line offerings from brands like Goldmund, Rockport, Basis, VPI, Teres & Continuum.