Vibration and Isolation

[Thoburn]

I am building a sandbox platform for my VPI Scout II turn table. It will consist of a 3/4 inch thick mahogany box with a 3/4 inch plywood base that is 1/2 inch up from the bottom of the sides. I have a 3/8 inch thick piece of polycarbonate that will sit on top of the sand. Under the box I am either going to use small tire inner tubes or Vibrapods. I have read good and bad things about sand boxes. Have any of you Bottleheads used a sand box platform or know somebody that does. I would appreciate some feedback on any type of turntable platform experiences.

Thanks!

 

[randy@matrixq.com]

If you have cats in the house, I wouldn't go the sandbox route.

 

[Grainger49]

Have a look at this on Wardsweb's site:

http://www.wardsweb.org/audio/isolation_table.html

 

[Thoburn]

Hey guys.

We have a cat, but unless he can do his business in a 1/4 inch slot while balancing on a 1 inch ledge I think I'm safe. Actually, I plan to put very soft 1/4 inch tubing between the edge of the polycarbonate and the sides of the box. Mostly to keep any sand dust from escaping and fouling up my records and table.

Thanks for the link. I have read that one and a bunch of others. The only negative I saw (and I can't remember where) was a guy that dished sand boxes and advocated inner tube(s) under a piece of MDF with roller blocks supporting the turn table. It has very bad WAF, but probably works well.

I will try to post info and results on my sand box experiment.

 

[Grainger49]

   .  .  .   inner tube(s) under a piece of MDF with roller blocks supporting the turn table.

I can't imagine this staying level two hours in a row, much less two days in a row.

I do want to try Wardsweb's idea with the glass bead media.  The drawback is you have to buy a whole bag of it and use about 1/4 of it.

My cat sleeps closed up in the listening room every night.  I keep the turntables covered so she doesn't jump on them.  She has her own box in the room too.

 

[Thoburn]

Hi Granger,

I like the glass bead idea to. IIRC you live in Colorado. I'm in Washington state. If we were closer I would happily split the purchase price with you.

 

[Doc B]

At Berkeley in the 70's we used a giant sand box on inner tubes to stabilize a holography setup that had to keep the vibration of the mirrors down to just a few wavelengths of the HeNe laser's output frequency for something like 13 seconds at a time in order to get a good exposure. The added challenge was that the laser setup was on the third floor of the building. One would set up a Michelson interferometer on the table and project the interference pattern on the wall, and then count how long the average period was before someone on the third floor would walk down the hall, close a door, or sit down at their desk and disturb the pattern. I thought it was pretty amazing that the thing worked so well.  IIRC the recipe was a 4'x8' sand filled table with inner tubes on top, with another sand filled 4'x8' box on top of that. I don't recall the top of the top box floating on the sand, I think it was attached to the sides of the box. Might have been a piece of slate from a pool table, or my old brain may just be embellishing...

 

[Thoburn]

I have the box up and running. It took all 50 pounds of play sand to fill it. And I can say that it is definately worth the effort. Imaging is improved. The instruments are more focused and there is more 'air' between them. The sound is more detailed. I would say that just about everything is a bit better. Will try to take some pictures when the light is better.

 

[Grainger49]

Hi Granger,

I like the glass bead idea to. IIRC you live in Colorado. I'm in Washington state. If we were closer I would happily split the purchase price with you.

I'm in Knoxville, TN.  I expect the cheapest shipping would cost the price of a whole bag of beads.  But thanks for the thought.

Won't the sand settle after a little while?  I suspect the glass beads do too.

 

[Thoburn]

Merry Christmas Granger,

Here is a design where settling is discussed.

<<http://cognitivevent.com/sandbox.html>>

 

[Grainger49]

That is pRC's site.  He was an old hand here when I arrived.  He is a materials specialist.  He knows a lot about vibrations and materials.  

I'll consume it soon.  Thanks for the link!

Merry Christmas to you and yours!

 

[Thoburn]

Here is the new rig.

 

[Thoburn]

Sandbox in relation to other gear.

 

[bainjs]

Grainger,

This may be a project we can share.  I've got the woodworking down, you can work on the design.  We could share a bag of beads.  I've also been wanting one for my Wadia iPod transport.

It's something we can discuss in Jan.

Joel

 

[Grainger49]

Sounds good!

Thoburn, your sand box looks better than my old VPI base.

 

[Thoburn]

Hi Granger,

I like the glass bead idea to. IIRC you live in Colorado. I'm in Washington state. If we were closer I would happily split the purchase price with you.

I'm in Knoxville, TN.  I expect the cheapest shipping would cost the price of a whole bag of beads.  But thanks for the thought.

Won't the sand settle after a little while?  I suspect the glass beads do too.

I forgot to mention that as I added layers of sand I tapped around the frame with a rubber mallet to get the settling started. It has been a couple days now and I don't see any uneven settling. The bubble level show the same on the platter as it did in the beginning.

 

[bainjs]

What feet did you end up using? 

 

[Thoburn]

What feet did you end up using? 

I picked up 2 canisters of racket balls at Target for about $8. I cut them along the seem with a one sided razor. It was surprising how tough they are. There are 12 half-balls under the sand table. You can see their turquoise bottoms between the shelf and the sand box. The bottom of the sand box is 1/2 inch up from the bottom of the sides. I think I mentioned that I used 3/8 poly instead of the 1/4 mentioned in the design. I went with the 3/8 because my Scout II table is about 40 pounds and I wanted to spread the weight around as much as I could.

 

[bainjs]

Thanks, that's a pretty good idea.

Some people also use small super balls sitting in rubber washers or o rings to keep them from rolling and just sit the base on them.

Sounds like some experimenting coming up!

 

[Thoburn]

It has been about a month now and I have been checking the level of the turn table. No change so far. I think the tapping with must have helped a lot. Very pleased with the results.