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So what about the plinth?

It just struck me that there was a great deal of discussion regarding reduction of vibration through the plinth, but in your situation, all of the vibration is occurring with elements already bolted to the top plate. So the plinth, and its vibration dampening magic, would be isolated from the main sources of the vibration, while they would be directly coupled to the platter and the pickup.

It would also be interesting to substitute the screws holding the armboard onto the plate and isolate them above and below the armboard with sorbothane or rubber donuts. Basically to "float" the armboard above the plate, rather than screwing it down to it.

Again, I'm hoping that those with more experience will weigh in on the merits, but it stands to reason (mine).

tromba said:
I never even thought about that. I wonder if anyone has done that.

I know on my other TT, a Sota, the motor is completely external.
Click to expand...
 
What I am especially trying to point-out is that not only the material that a plinth is made from matters. The shape of the plinth, location of fixtures (ie arms and motors) all will have an audible effect. The interface between the plinth and the surface that supports the plinth. The sonic properties of the support.

There is much more to be considered than the material of the plinth. Much of what takes place in the audio sphere is the following of trends or the following of other enthusiasts with very little investigation of or understanding of basics which underpin the subject of discussion.

Just like vibration of the air in a room displays areas of high pressure and low pressure when excited by a pair of speakers, a solid object displays areas of vibrational nulls and vibrational peaks as it is excited by resonances. The distribution pattern of these nulls and peaks change position with different frequencies. Watch this video:

http://www.youtube.com/watch?v=ouAUo9jVtAU

There is much more to what is going on in a turntable than materials. If waterjetguy will explain all of this and more, it will be welcome.
 
theophile said:
There is much more to be considered than the material of the plinth. Much of what takes place in the audio sphere is the following of trends or the following of other enthusiasts with very little investigation of or understanding of basics which underpin the subject of discussion.
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IMO a person who has an ear for what sounds good can come to many excellent conclusions without a single whit of the science behind it.

marc mc
 
marc mc said:
IMO a person who has an ear for what sounds good can come to many excellent conclusions without a single whit of the science behind it.

marc mc
Click to expand...

I agree, but someone has put his hand up to explain it all scientifically. If that is the case, I would like the explanation to be thorough not limited to materials alone. There are many more factors that influence the end result than the materials that the plinth is made from.
 
theophile said:
I agree, but someone has put his hand up to explain it all scientifically. If that is the case, I would like the explanation to be thorough not limited to materials alone. There are many more factors that influence the end result than the materials that the plinth is made from.
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I plan to dig a lot deeper, but first we'll have to cover the basics of vibration more thoroughly, so that everyone can understand the discussion.

Give me a little time to put some material together. I'll probably explore resonance/natural frequency next, since it's fundamental (engineering/music pun here, do you get it?) to the control of vibration and is widely misunderstood by the audio community.

As mentioned in an earlier post, I can address the science behind the design of turntables/tonearms/cartridges, but I'm not a designer of any of them. That means that I can't tell you exactly which materials, what thicknesses, will work best in a given situation, for instance. But I can tell you what you should be trying to achieve and offer some good ideas to try. Understanding how a TT really works will give you a lot of insight as to how to improve one or choose one. And it will likely shorten the R & D for any mods by a wide margin.
 
tromba said:
LOL!! I just went to google, entered "sorbothane feet" clicked on images, and scrolled until I found one JUST LIKE YOURS!!! I clicked on that image and it brought me right here to this thread!!! :D So where did you get yours?
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Right here:

http://www.ebay.co.uk/itm/350429906421?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

They are not cheap, but not super expensive either. These guys don´t ship worldwide, apparently, so if you want a set, just let me know, we can arranje something, I´m sure.
 
This is a resulting build, from the author of those numbers, audioqualia.com, (cut and pasted numbers from other real academics and researchers):
p1014063.jpg

http://qualia.webs.com/plinths.htm

Pretty awesome stuff, ehh?
 
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At Vinyl Engine, in a post on mushrooms, a forum member J.D. posted (used by permission):

"the prevailing wisdom seems to be to tie that TT as directly to a high mass plinth as possible".

That's the wisdom of our era, and the view of the (originally japanese) renaissance-analog movement that valued resolution over convenience. Hence, direct-coupled-no-shrooms, heavy layered-attenuating plinth, which drains motor & other resonances down and away from the chassis. The plinth then situated on a solid rack or wallshelf is generally disinclined to move the stylus with footfall, etc, but isn't shock/shellproof.

Contrarily, the intent of the original manufacturer was to insulate Thorens from consumer complaint regarding 'skipping' by the use of compliant mushrooms that --while convenient re skips---- contain and restrict the motor/other resonances to the chassis, and hence keep them more audibly bouncing around in the vicinity of the cartridge & stylus. (Garrard included optional-use springs with their 3/4o1s, stipulating that in case of footfall problems they could be installed. )

Viewed in a strictly consumer-manufacturer-relations context, a little noisefloor in a customer-installed (many were plinthed by customer, in consoles, etc, so not always solidly rigged...) turntable was preferrable to having dissatisfied customers whose records skipped at the least provocation.
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I read this as mushrooms aren't the best, but given that many consumers wouldn't have a "proper" plinth, the mushrooms help the more prevalent problem that could be caused by skips

J.D. from Vinyl Engine replied in an email:

but that given the choice of providing high-rez gear that most consumers wouldn't get installed correctly, or relenting a little and providing shock-absorbers-- they were practical and provided the extra insurance.
Click to expand...
 
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waterjetguy said:
Hmmm, must be the development test mule...

I wonder where he applied all of that great data.:scratch2:
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Adding in post edit - a link to his own website describing this build:
http://qualia.webs.com/plinths.htm

That was what he raved about for a couple of years.
In that same amount of time, I knocked out 5 plinth builds; two of stone, two of birch ply, and a wooden butcher block internal reinforcement of a stock plinth to bring it to a "massive" condition, yet retaining the stock external appearance.
Also, in that same time, he publicly belittled any number of other plinth builders who were actually building plinths, putting their theory to test, and sharing the results, and spawning open lively, constructive discussion.
When pressed to show proof of his designs, we were told that we were not worthy of seeing his efforts.

I'll bow out now; just know what the source of those numbers, and that website have, to back up their words.


Mods and all:
Apologies for dragging drama into this thread, but I gotta call BS when so many potential new plinth builders are so drawn into his rhetoric.
By now you all should know that this isn't my usual demeanor here, and I do apologize for it.
 
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mfrench said:
Mods and all:
Apologies for dragging drama into this thread, but I gotta call BS when so many potential new plinth builders are so drawn into his rhetoric.
By now you all should know that this isn't my usual rhetoric here, and I do apologize for it.
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I appreciate your comments. All I know is that everything I read on the internet MUST BE TRUE!!! Or at least until I read another side of it!!! And on most of this topic I don't know enough to make the best conclusions without knowing who is writing.
 
jgordon said:
It just struck me that there was a great deal of discussion regarding reduction of vibration through the plinth, but in your situation, all of the vibration is occurring with elements already bolted to the top plate. So the plinth, and its vibration dampening magic, would be isolated from the main sources of the vibration, while they would be directly coupled to the platter and the pickup.
Click to expand...
As I've thought about this, it now seems logical that the rubber mushrooms are not the best thing to use and perhaps bolting the table to the plinth would better reduce vibration.

As has been suggested, I'll probably try it both ways -- some have said for their situation mushrooms are better, some not.

But it is true that all vibration and noise come from the top -- the TT itself (this assumes a massive enough plinth on a solid foundation that room vibrations don't enter into it.)

I'm still wondering about how much heat is generated by the motor (my table is currently out of town at the shop). In the original plinth the only air getting to the motor was by way of space provided by the mushrooms. If those are removed, I'd think then feet would be required (and of course an opening in the bottom of the plinth) to dissipate heat.

For TD-124 users: is this no big deal as long as some air can get there? Or is heat a serious problem that needs to be allowed for?
 
"Contrarily, the intent of the original manufacturer was to insulate Thorens from consumer complaint regarding 'skipping' by the use of compliant mushrooms that --while convenient re skips---- contain and restrict the motor/other resonances to the chassis, and hence keep them more audibly bouncing around in the vicinity of the cartridge & stylus."

- This is basically exactly what I was saying, only more eloquent and backed by greater knowledge.


tromba said:
As I've thought about this, it now seems logical that the rubber mushrooms are not the best thing to use and perhaps bolting the table to the plinth would better reduce vibration.
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Not sure that it's a case of absolutes. I'd say that if you keep the motor attached to the top plate, then yes - you'd want to bolt everything to the plinth. However, if you detach the motor from the top plate and bolt THAT to the plinth, I'd say isolate the top plate as much as possible. Not sure what shape your mushrooms are in, but mine are fairly hard. You might even want to investigate various materials and shapes to further isolate the top plate. I know I have a trip to some plumbing supply shop or some such place in my future to see what I can find for substitutes. They make all sorts of stoppers in all sorts of shapes and materials, and I find it hard to believe that the mushroom shape and rubber remains the best thing for these tables.

tromba said:
As has been suggested, I'll probably try it both ways -- some have said for their situation mushrooms are better, some not.
Click to expand...

Agreed, although this might get spendy, unless you have a plinth that has both mushroom insertion points and top plate attachment points. I guess if your friend is building it, you can have it both ways. How would you bolt the top plate down?


tromba said:
But it is true that all vibration and noise come from the top -- the TT itself (this assumes a massive enough plinth on a solid foundation that room vibrations don't enter into it.)
Click to expand...

Yes, I had assumed that. If you don't have a stable platform, none of this really applies. You'd be looking at the plinth more as an isolation tool than a vibration sink. And then I think the conversation would move more toward sandboxes and other means of low frequency or footfall-type dampening.

tromba said:
I'm still wondering about how much heat is generated by the motor (my table is currently out of town at the shop). In the original plinth the only air getting to the motor was by way of space provided by the mushrooms. If those are removed, I'd think then feet would be required (and of course an opening in the bottom of the plinth) to dissipate heat.

For TD-124 users: is this no big deal as long as some air can get there? Or is heat a serious problem that needs to be allowed for?
Click to expand...

I'd be curious about this as well.
 
And, as I tear into mine more, I'm realizing it would be fairly easy (for someone smarter and more skilled than myself) to detach the motor from the top plate and bolt it to the plinth. The motor mounts are extensions of the case bolts. Frankly, it looks as though you could simply get another one (to replace the floating third mount), and flip them upside down to support the motor from below. Then it's just a question of measurement and construction of a plinth that will support the motor at the correct height.

I wonder why no one's tried this (to my knowledge).
 
Mmmn, seems to me to many massy plinth designs concentrate on isolating the turntable from the outside world. In reality this is less of a problem than it is made out to be. Yes, if you have a badly sited deck, you may suffer from air born vibration from the speakers themselves. If you are very close to a main road you may have traffic shocks. Footfall is only a problem if you move about, I tend to sit still and listen. I think for most of us these elements are not an issue.

The real problem areas are noise from the motor and noise from the main platter bearing getting to the cartridge. If these two items were given higher priority then better results would be achieved. That's not to say I don't mind a bit of mass in my decks (concrete) I just don't think its a cure all. If your motor is mounted on a flimsy top plate and the armboard is attached to the same, sitting it all on top of a block of masonry, or a jelly or teaching it to levitate using springs aint going to cure much.

So think about which bits you want to couple and which you want to decouple to allow the cartridge to see the vinyl unmolested. :D
 
Qwin said:
If your motor is mounted on a flimsy top plate and the armboard is attached to the same, sitting it all on top of a block of masonry, or a jelly or teaching it to levitate using springs aint going to cure much.
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I've spent some time trying to get it to levitate, but no successful results yet!!!

I'm going to search wider to see if I can find anyone who has moved this Thorens motor to the plinth. As far as the armboard, I don't know how best to fix that. The arm isn't long enough to bypass the armboard and mount to the plinth. Built a slate armboard or something?
 
jgordon said:
And, as I tear into mine more, I'm realizing it would be fairly easy (for someone smarter and more skilled than myself) to detach the motor from the top plate and bolt it to the plinth. The motor mounts are extensions of the case bolts. Frankly, it looks as though you could simply get another one (to replace the floating third mount), and flip them upside down to support the motor from below. Then it's just a question of measurement and construction of a plinth that will support the motor at the correct height.

I wonder why no one's tried this (to my knowledge).
Click to expand...

people do detach motors from idler drive tables. I remember reading a couple of articles about it. I will dig around and see if I can find something for you , I am pretty sure it was being done with garrard 301/401's but I could be wrong on that.
 
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