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PostPosted: February 4th, 2015, 9:03 am 
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About Grizzly Bench Tops: the Grizzly G9912 (36" x 24") is $10 cheaper directly from Grizzly than from Amazon. Just sayin'. :thumbup:

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PostPosted: February 4th, 2015, 9:08 am 
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tomp wrote:
For may turtable I built a box out of MDFD and then filled it with sand. I then placed it on four Sorbothane feet that I had but could just as easily have used squares cut out of sheets. To get a thicker pad you can just use more squares stacked on top of each other. You can get them online from many places. Like any rubber material you should use something to keep it off finished wood to prevent staining.

Tom, I like your approach, and I looked at the Sorbothane web site: interesting information there. I can see getting the Sorbothane hemispheres and putting them under a sand box.

My turntable has a separate motor box - I should experiment with isolating the motor box from the turntable, which would both be on the sand box. Interested to know if there is noticeable transmission from the motor to the tonearm through the plinth.

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PostPosted: February 4th, 2015, 9:09 am 
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Sorry, I'll stop hijacking this thread about racks to discuss turntable installation. :oops:

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PostPosted: February 4th, 2015, 9:54 am 
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Guy wrote:
Sorry, I'll stop hijacking this thread about racks to discuss turntable installation. :oops:


No hijack here, Mr. Guy. I am very interested in turntable isolation.

Allegedly mine has 48dB of isolation from it's platform. Even if true, that still isn't 100+dB, so effects may still be there. Interesting discussion and food for thought.

Stuart


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PostPosted: February 4th, 2015, 11:23 am 
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Guy wrote:
About Grizzly Bench Tops: the Grizzly G9912 (36" x 24") is $10 cheaper directly from Grizzly than from Amazon. Just sayin'. :thumbup:


Item price, or shipped price?

Roscoe

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PostPosted: February 4th, 2015, 11:55 am 
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Stuart Polansky wrote:
Guy wrote:
Sorry, I'll stop hijacking this thread about racks to discuss turntable installation. :oops:


No hijack here, Mr. Guy. I am very interested in turntable isolation.

Allegedly mine has 48dB of isolation from it's platform. Even if true, that still isn't 100+dB, so effects may still be there. Interesting discussion and food for thought.

Stuart


The level of isolation is only one factor in the equation with a turntable. The frequency of the vibrations that get through are also important. As the frequencies go below the arm/cartridge resonance, the ability of the cartridge to respond to those vibrations decreases. Just for grins let's say we can get the vibration down to 1/100 Hz (good luck with that). It would be like gently raising and lowering the turntable the very slight distance caused by the vibration. There would be no audible results. For an audibility standpoint, you are better off with slightly higher vibrations below resonance than slightly lower vibrations above resonance. The good thing about the mass - compliance solution that uses Sorbothane is that it not only greatly lowers the resonant frequency, but the Sorbothane absorbs much of the vibration in the first place.

Tom


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PostPosted: February 4th, 2015, 12:24 pm 
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the question I have is whether you want to sink the vibrations in the turntable, or prevent vibrations getting into the turntable from outside sources. I think some of the conventional wisdom is that the turntable picks up ambient vibrations, say from the air/speaker source, and thus you would want to remove, ie. sink, that vibration away. The other side is that the support itself is subject to the same vibrations and you want to keep those vibrations from getting into the turntable system, thus you would isolate the turntable from those vibrations. And thus you would use two different methods for reducing the vibrations in a turntable...


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PostPosted: February 4th, 2015, 3:36 pm 
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The area of a rack shelf that can pick up airborne vibrations is generally much larger than the area of a turntable base. Add to that the much larger area of the floor that will also pick up reflections and the numbers get worse. Since the vibrations are oscillatory in nature I don't see how you can shunt them one way out of the turntable to something else as a rectifier does with AC electrical signals. That would require a unidirectional movement of the base which would be resisted by the shelf. If you attach the base securely to the shelf what you are actually doing is increasing the effective mass of the base but in doing so you are linking it to a larger vibrating plane. You could also get complex vibrations by the interaction of the two but I could not hazard a guess as to what that might be.

If you are concerned about airborne pickup by the turntable base which is the smallest of all the areas involved perhaps it is worth trying to first isolate it from the larger vibrating sources and then try to increase the mass of the base itself to increase the mass part of the mass - compliance equation and decrease amplitude. You could then add a substantial amount of damping material that will convert the remaining vibrations to heat. Just guesses on my part. The problems I have encountered have primarily come from floor and shelf vibrations being transmitted to the turntable base. Removing those problems seemed to solve the issue for me. Am I missing further improvement? Could be, but I think going further may get you into the area of diminishing returns. It would be an interesting project.

Tom


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PostPosted: February 4th, 2015, 3:41 pm 
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I just had another idea. I may have been very successful with the removal of problems by concentrating on isolation from the shelf because my turntable is in a closed cabinet while the music is playing. That is a fairly easy fix. You can build a small enclosure that is insulated to reduce airborne vibrations from reaching the isolated turntable in the first place.

Tom


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PostPosted: February 4th, 2015, 3:50 pm 
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Stuart Polansky wrote:
Item price, or shipped price?

$95 + $15 shipping. :handgestures-thumbupleft: I haven't bought one :shock: , so I don't know for sure if there is some hidden fee, or if they ship it on the back of a dog, but that's what the web site lists.

Try http://www.grizzly.com/products/G9912

I've found in the past that Amazon doesn't always have the lowest price, but the Prime-free shipping is nice. Always take a minute to shop around. :shifty:

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