Damping the analogue "setup"

I assumed it is not such a serious issue.

It is a most serious issue......
We have found that suspended concrete floors have intense inbuilt stresses because of the spans......and these stresses cause lower ever-present Structure-Borne sound than those present in suspended timber floors.
Modern high-rise apartment buildings are particularly susceptible because of the prevalent use of prestressed concrete floor slabs which allow for thinner thicknesses and less steel reinforcement.....but also permit greater movements, bounce and structure-borne sound between 2 Hz-10 Hz.
These frequencies are almost impossible to eliminate from floor-mounted stands and that is why your turntable and phonostage are sounding differently with each and every change in support material.

take a look at some of the products from herbie's audio. They have a wide variety of damping products that may suit your needs. I am using some terrastone footers and a terrastone plinth for my table that was made by edensound. They also make a good selection of footers and isolation products. Dan is great to work with. I highly recommend his terrastone products.

Hi Pani, I do read your posts, also those over at AA. I may miss your conclusions of some of your post questions. Have you found a replacement for your Tannoys yet? (I do 300B & 45 amplification)

Hi, I went around looking for alternatives for a short period. Turned out that Tannoy Alnico magnet versions would work well with my amp, so will Altec 604 and Audio Note ANJ speakers. However I have realised that it will not be easy for me to leave the Tannoy presentation. Also, it is difficult to get an Altec 604 because it will need to be custom made and mostly will have to be bought without an audition. Audio note is an alternative that I have saved for the last. In the mean time I have stopped worrying too much about this and just started listening to music and made sure I dont pump it up too loud for the amp to be stressed. I also realized that moving from a traditional SS amp to an SET made the music very direct which is exciting the room nodes to a much higher degree hence it needs some treatment before I could go any louder.

It is a most serious issue......
We have found that suspended concrete floors have intense inbuilt stresses because of the spans......and these stresses cause lower ever-present Structure-Borne sound than those present in suspended timber floors.
Modern high-rise apartment buildings are particularly susceptible because of the prevalent use of prestressed concrete floor slabs which allow for thinner thicknesses and less steel reinforcement.....but also permit greater movements, bounce and structure-borne sound between 2 Hz-10 Hz.
These frequencies are almost impossible to eliminate from floor-mounted stands and that is why your turntable and phonostage are sounding differently with each and every change in support material.

Thanks for that gyan Halcro. It makes my life easier to think that it is an issue that is too far embedded in the structure for me to be able to solve it, so I need to kind of ignore it and move on. May be I can just try some decent isolation platforms and see if it makes for a more enjoyble listen and settle down. I was considering a Vibraplane but a friend of mine who has heard a Verdier on Vibraplane said it leans out the sound a touch too much so it is not really a good match (according to him).

take a look at some of the products from herbie's audio. They have a wide variety of damping products that may suit your needs. I am using some terrastone footers and a terrastone plinth for my table that was made by edensound. They also make a good selection of footers and isolation products. Dan is great to work with. I highly recommend his terrastone products.

Thanks for the pointer, I will check out Herbie's products.

Pani,
If you can find a concrete wall or column in your listening room......then you can mount a support shelf for the turntable.
The columns and supporting walls are not subject to the spanning stresses that the suspended floors are and thus do not carry the same low frequencies within.

From the OP:

The problem is, the overall sound can vary vastly from lean-strident to round-warm very quickly based on what kind of spike base I use underneath the rack.

Most of the comments above, including Halcro's insights, assume that the sonic character of Pani's table varies with the spikes beneath his rack because the spikes provide different degrees of isolation from floor-borne vibrations. While such vibrations certainly exist, in my opinion they're not the main source of what Pani described. Other vibration sources are more likely to produce the described effects.

The other gear on the rack is a noise source, both from its native vibrations and from the musical energies it's reproducing. The turntable motor is another noise source, and some PV motors are notoriously noisy. Stray energies leaching from the stylus-groove interface are the most influential noise source of all, since they're closest to the pickup.

These noise sources produce stray energies in the audible band, not just at 2-10Hz, and they're physically and acoustically closer to the TT than vibrations from the floor. The footers beneath a rack have a profound influence in a setup's ability to drain these vibrations away from the TT - or not.

Reducing stray energies in the 2-10Hz range will lower the system's sound floor, but it's unlikely to change the sound "from from lean-strident to round-warm" or vice-versa. IMO, such changes are more likely due to changing stray vibrations in the audible frequency range, such as are caused by the factors noted above.

That said, a wall mount such as Halcro suggests would address both structure-borne and equipment-borne vibrations, as it would isolate the TT from both. They'll have less effect on TT motor noise and vibrations emanating from the stylus-groove interface, which must be addressed by other means.

It's far from a simple problem and there is no single solution.