[Curly Woods]

Good info, jrtrent, but here's the link that kind of contradicts it....

http://www.vinylengine.com/phpBB2/viewtopic.php?t=5195

I would not want any additional suspension under a turntable, personally.  I feel that the table needs to be stable to allow the cartridge to trace the grooves without undue influence.  I prefer to have a rigid platform for any table to work from rather than to add another variable to the mix.  But this is simply my opinion and everyone can and will have their own.

[jsaliga]

There is far from a concensus on this subject and credible opinion can be found on either side of the topic.  I don't find this surprising at all.

--Jerome

[Browntrout]

To quote a part of your post Wayner...
  "Suppose we are sitting at the kitchen table and on top of the table we have a piece of paper and a steel bearing, like 3/8" in diameter. If we were to blow on the bearing, it probably won't move. If we blow on the paper, it will will move. If we now hit the table with our fist, the stupid piece of paper just sat their and the bearing jumped into the air. This proves in a small way that lesser mass responds to air (and airborn vibrations, while real mass responds to wave lenght transmission thru other objects."

  This does not prove what you say. The reason the paper might stay still (as in move with the table) is to do with it's shape (air pressure over a relativley large surface area keeping it pressed against the table when the table moves upwards) and lack of rigidity and texture (providing a good amount of surface friction with the table top) not it's weight. The reason the bearing moves is also because of it's shape and the fact that it is hard. Hard things do not tend to deform rather transmit energy through themselves into something else or move carrying that energy with them.
 ..........and before someone says it, I don't think you are stupid.

 

[toobluvr]

Good info, jrtrent, but here's the link that kind of contradicts it....

http://www.vinylengine.com/phpBB2/viewtopic.php?t=5195

You will always find disagreements!

Talk to two audiophiles and you'll get three different opinions!

 

[jsaliga]

^
+1

--Jerome

[guest48077]

Here is my DIY Turntable stand, Right now I like the results I am getting. Sand in the Drawer ( about 60 pounds) sand in the Sandbox (about 60 pounds) The sand box floats on 5 raquets balls. I did it this way for rigidity with a little side to side motion. What does everybody think am I going about this the wrong way? Open for criticism. I am using a project debut III, the intro table





Thanks

[doug s.]

the massive vs lightweight support for turntables issue may be compared to how earthquakes affect the surrounding areas, depending on the geography.  tho rare, a future earthquake at the new madrid, mo fault will (and has) generated energy felt much farther away than those along the more well-known california faults.  this is similar to why a massive turntable stand can be excited by low frequencies much more than a light rigid stand - the land around new madrid is much more rigid than what's around the california faults.

http://www.essortment.com/all/newmadrideart_pvm.htm

doug s.

[doug s.]

Here is my DIY Turntable stand, Right now I like the results I am getting. Sand in the Drawer ( about 60 pounds) sand in the Sandbox (about 60 pounds) The sand box floats on 5 raquets balls. I did it this way for rigidity with a little side to side motion. What does everybody think am I going about this the wrong way? Open for criticism. I am using a project debut III, the intro table





Thanks

what are you doing wrong?  your isolation set-up looks fantastic!     seems it is worthy of a better turntable!   

doug s.

[Wayner]

To quote a part of your post Wayner...
  "Suppose we are sitting at the kitchen table and on top of the table we have a piece of paper and a steel bearing, like 3/8" in diameter. If we were to blow on the bearing, it probably won't move. If we blow on the paper, it will will move. If we now hit the table with our fist, the stupid piece of paper just sat their and the bearing jumped into the air. This proves in a small way that lesser mass responds to air (and airborn vibrations, while real mass responds to wave lenght transmission thru other objects."

  This does not prove what you say. The reason the paper might stay still (as in move with the table) is to do with it's shape (air pressure over a relativley large surface area keeping it pressed against the table when the table moves upwards) and lack of rigidity and texture (providing a good amount of surface friction with the table top) not it's weight. The reason the bearing moves is also because of it's shape and the fact that it is hard. Hard things do not tend to deform rather transmit energy through themselves into something else or move carrying that energy with them.
 ..........and before someone says it, I don't think you are stupid.

 

You missed my point completely. As the frequency goes up, the effect on mass diminishes (from airborn vibrations) and as the frequency goes down, the effect on mass increases (ala, the earthquake point). However, unless you have enough energy to move (as example) a 60 lb piece of granite or undertowogt's cool 60 lb sandbox, the effect is moot. It can't move it because it doesn't have enough power (as say, from a pair of speakers).

Wayner

[Browntrout]

I don't know enough about the nature of air to solid transmision, I assume there is always a percentage that is reflected and a percentage that is absorbed and probably some that goes through without doing much.
   A point I would like to add is that the stand does not have to move at all to transmit the energy into the turntable. As in the metal ball in the middle of Newtons Cradle.
  The speed at which energy can enter and leave the stand/object is really the only thing we can alter (and perhaps the way it behaves at certain frequencies) and thankfully whether it is appealing to the eye.

[jrtrent]

Good info, jrtrent, but here's the link that kind of contradicts it....

Interesting series of papers, though I don't know that it contradicts the points raised by Linn; it's just another approach to the problem.  Maybe Linn read Grado's paper, because in 1991 they introduced the Trampolin baseboard, which had damping feet specifically designed for use when the LP12 had to be sited on heavy furniture.  Like the earlier Custom Woodwork and Design isolation platform (just a light, rigid board with leveling feet to decouple the turntable from the mass of the furniture), it was only needed when circumstances forced you into a compromised turntable placement.  One thing both Linn and the Grado article agree on is the need for a springy support such as the Trampolin or the arrangement described by Grado to be tuned to the specific turntable you're putting it under; it's not a one-size-fits-all solution.

[Wayner]

Objects need mass and length that are sympathetic to wave lengths to start to vibrate (at resonance frequencies, or orders of). While some of my examples were piss poor at getting my point across, I'll try it from this angle. If we look at frequences (octives) thru our hearing range, they would be:

20
40
80
160
320
640
1280
2560
5120
10240
20480

Now we know that the speed of sound (as a standard with a specific air density, air temp) to be at 1,125 feet per second. Now we can figure out the length of each of those frequency's wavelength. So:

20 = 56.25 feet
40 = 28.13 feet
80 = 14.06 feet
160 = 7.03 feet
320 = 3.51 feet
640 = 1.75 feet
1280 = 10.54 inches
2560 = 5.27 inches
 5120 = 2.63 inches
 10240 = 1.38 inches
 20480 = .69 inches

Now if we have a turntable stand that is 24" x 24" x 48", we can see that wavelengths around 320 and up will be frequencies that will be sympathetic to our table dimensions. However, most of those frequencies, especially the higher frequencies, have lost power. Now here is where the problem comes in to being. What happens if we are in a room that is 24 x 16 x 8? It looks like a 50 hz bass note is going to fit nicely into the room. It may find a resonance frequency, where this energy is exploited, and create a vibrating node. This vibration will affect things that are in contact with it. Therefore, if we have a light stand (even tho it's ridgid), it may vibrate if it doesn't have enough mass to absorb the energy. If you have ever had a picture hanging on the wall that would buzz on certain bass notes, it really wasn't the picture vibrating from the bass note, it was the wall the picture was hanging on that made the picture vibrate, because the wall's length was sympathetic to the wavelength, perhaps hit it's resonance frequency(s) and vibrated like a mad man.

Wayner 

[macrojack]

Wayner - I see nothing wrong with your thinking. It is intuitive and you provide arguments and examples that seem credible.

Perhaps it would help this discussion if we differentiate between physical influences like a structural vibration that carries into the stand through physical transmission and airborne vibrations that might excite the turntable stand by resonating it at whatever frequency its design leaves vulnerable.

Complete physical isolation will not prevent airborne vibrations from causing some or all of the arm/table parts from singing along in sympathy to 72 hz. Mass has no bearing in this instance.

And would it indeed be possible that mass can work against us in certain instances? A five pound battering ram will not likely knock a door down whereas a 5,000 lb. ram would take the door down with no resistance.

Likewise, if our 5,000 lb. turntable stand vibrates in response to low frequency energy, it will ram the turntable it supports. A five pound stand can vibrate in the same way with indiscernible consequences.

Again, I am approaching this with no training, just imagination. Does my theory make any sense?

[Wayner]

macrojack,

I agree with you. If we had our table on the worlds largest immovable object, the table could still (and does) vibrate. I think that's the trick to the whole thing, is that it is not just a simple equation, but rather a series of attempts to neutralize vibrations. Frank likes plasticaly (and so do I) as it goes thud when you throw it at something. That is why some folks put the clay in their TT base (or on the outside, like John TCG), turning that unwanted energy into heat. The table I built (ARMod) has an interior cavity in the body that is filled with plasticlay and then sealed. My stand alone motor also has a cavity filled with clay to kill some of the motor vibrations. My granite base does the rest.

Wayner 

[macrojack]

So could it be said that one approach resists or suppresses external forces and the other attempts to redirect them, a la martial arts? The Aikido Stand?

[Wayner]

If a component is the same length as a frequency's wavelength, and it's light enough, and not damped properly, it will vibrate at that frequency (thru the air). The other vibrations will come via connected components via mechanical connection. The floor board was 28.13" long and vibrated like a bastard when the frequency (with sufficient volume) hit 40hz. The leg of the TT stand was on that board.

These are the same nodes that cause speaker placement problems. Put the speaker in a position where the nodes can amplify and create resonance, now we have more fun trying to suppress those nodes. It is about math and some of these kinds of things can be solved with proper speaker positioning, even in bad rooms. One formula that I found from my lighting career was the .29 times factor. This was a great number to stop lots of vibrations from turning into resonances and their wonderful cousins, the harmonic frequencies. So for example if you have a room that's 16 x 20 feet, take 16 x .29 (convert to inches) that would be 4.64 feet. That means along the 16 foot wall, your speaker in that direction should be 4.64 feet from the end wall. The other wall is 20 feet so that figures out to be 5.8 feet from the outer wall, giving you a distance of 8.4 between speakers. This is also another reason I like the speakers along the long wall, not the short wall, cause then they are too close together, and I like to hear "stereo". This configuration is supposed to keep lots of wavelengths from fitting into a room and also squelch any of their also unwanted harmonics.

Wayner