2. analog
  3. 183296-174921

Concrete Slabs

Here I go, perhaps stirring up some controversy.

I have two turntables, both sitting on a 400lb 17th century oak chest. The chest in question sits on a suspended wood floor in a 1985 post and beam house. I just started to play Mahler's 9th (DG/Guilini/CSO) on an SME 10 with an Ortofon Cadenza Bronze. It sounds as it should. But the point is that if I stamp as hard as I can right next to the chest, there is no interruption of the sound. Even if I take a deep breath and jump with both feet off the floor—nothing, nothing at all. So, tell me, what may I gain by pouring concrete here, there, and everywhere (as I believe someone once sang)?

Is this reverence for the ultimate solidity of a foundation the same kind of daftness as when someone says an interconnect must be as thick as their wrist, even though the component may pass the same delicate signal through a PCB trace of minuscule cross-sectional area? What are we aiming for?

dogberry

Showing 1 response by williewonka

williewonka
3,072 posts
 

@dogberry - It would appear that you have no problem, so pouring concrete would provide no improvement

But for those of us that do not have a 400lb chest to sit our TT’s on...

My TT is on a metal rack with 1/2" mdf shelves, but to isolate the TT from air-borne vibrarions I did the following

  • between the rack and the shelf I placed small pieces of sorbothane
  • on top of the shelf is a layer of thin foamed rubber
    • the kind used for lining drawers that can be bought from the $ store for $2 a roll
  • on top of the foamed rubber is a 1/2" grante tile cut to size
  • the turntable sits on that using large 2" bronze cone feet

The net effect of this "sandwhich" is stunningly quiet playback. I am unable induce vibrations into the turntable

  • even hitting the turntable deck with my knuckle only results in a very small thud.
  • hitting the rack in a similar manner produces only the very faintest sound

The "sandwhich" approach works because of the different densities of the materials used, so the vibrations have a hard job of transcending those boundaries.

The trick is NOT to make any one layer exceptionally thick, because then you can get vibrations occuring in that layer of material e.g.

  • if too thick, a granite tile/block will ring - 1/2 -3/4 inch works nicely
  • if too thick, sorbothane will reduce dynamics - 1/10" thick is ample
  • NOTE: I d onot use butcher blocks because I have found they have a sonic signature
  • MDF for shelves is excellent - it does not ring and has no sonic signature
  • see: this link Isolation Tips

Regards - Steve

 

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