Turntable "suspended in a vacuum" to prevent vibrations?

On this page

http://www.bornrich.org/entry/top-10...ve-turntables/

Look at number 5 - the description of the Continuum Caliburn includes
this phrase:

"The turntable employs a magnetically levitated magnesium platter,
which is suspended in a vacuum to guarantee there are no vibrations."

Suspending in a vacuum sounds like a contradiction in terms. A vacuum
tends to draw things in. At some point the turntable has to be riding
on some kind of bearing - i.e. something solid has to be contacting
something solid - which AFAIK provides a potential conduit for
vibration transmission. From a theoretical standpoint, how would you
"suspend" something like this in a vacuum in a way that guarantees no
vibration?

And of course a vacuum requires a seal, which sounds like something
with the potential to fail.

muzician21 > wrote:
>On this page
>
>http://www.bornrich.org/entry/top-10...ve-turntables/
>
>Look at number 5 - the description of the Continuum Caliburn includes
>this phrase:
>
>"The turntable employs a magnetically levitated magnesium platter,
>which is suspended in a vacuum to guarantee there are no vibrations."
>
>Suspending in a vacuum sounds like a contradiction in terms. A vacuum
>tends to draw things in. At some point the turntable has to be riding
>on some kind of bearing - i.e. something solid has to be contacting
>something solid - which AFAIK provides a potential conduit for
>vibration transmission. From a theoretical standpoint, how would you
>"suspend" something like this in a vacuum in a way that guarantees no
>vibration?

It is magnetically suspended. The vacuum will prevent air currents from
moving the plinth around. However, the vacuum will also change the damping
of the cartridge somewhat, and I am not sure what it will do to the
record/stylus interface.

>And of course a vacuum requires a seal, which sounds like something
>with the potential to fail.

Yes, of course. Machinery is like that.
rec.audio.opinion removed from the Newsgroups: line for the obvious reasons.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Suspending something in a vacuum does not, in and of itself "prevent
vibrations". Whoever wrote this promotional material has little practical
understanding of physics.

"Scott Dorsey" > wrote in message
...
> muzician21 > wrote:
>>On this page
>>
>>http://www.bornrich.org/entry/top-10...ve-turntables/
>>
>>Look at number 5 - the description of the Continuum Caliburn includes
>>this phrase:
>>
>>"The turntable employs a magnetically levitated magnesium platter,
>>which is suspended in a vacuum to guarantee there are no vibrations."
>>
>>Suspending in a vacuum sounds like a contradiction in terms. A vacuum
>>tends to draw things in. At some point the turntable has to be riding
>>on some kind of bearing - i.e. something solid has to be contacting
>>something solid - which AFAIK provides a potential conduit for
>>vibration transmission. From a theoretical standpoint, how would you
>>"suspend" something like this in a vacuum in a way that guarantees no
>>vibration?
>
> It is magnetically suspended. The vacuum will prevent air currents from
> moving the plinth around. However, the vacuum will also change the
> damping
> of the cartridge somewhat, and I am not sure what it will do to the
> record/stylus interface.
>
>>And of course a vacuum requires a seal, which sounds like something
>>with the potential to fail.
>
> Yes, of course. Machinery is like that.
> rec.audio.opinion removed from the Newsgroups: line for the obvious
> reasons.


but if the magnets vibrate would not the change in flux vector cause a
vibration in the suspended object
George

George's Pro Sound Company > wrote:
>
>but if the magnets vibrate would not the change in flux vector cause a
>vibration in the suspended object

Yup! Magnetic suspension is hard to make work properly.... you need to have
a constant flux over a wide area so that if the base vibrates, the field
at the plinth magnets doesn't change much if at all. You can make it work
but it's hard to make it as effective as cheaper alternatives.

On the other hand, those cheaper alternatives ALSO require some careful
engineering and they don't always get it. I can think of a mastering house
in NYC that was having trouble with building vibration from the subway and
installed a fancy isolated platform whose suspension had a resonance around
0.5 Hz which would get excited into wild motion by the subway....
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Scott Dorsey" > wrote in message
...
> George's Pro Sound Company > wrote:
>>
>>but if the magnets vibrate would not the change in flux vector cause a
>>vibration in the suspended object
>
> Yup! Magnetic suspension is hard to make work properly.... you need to
> have
> a constant flux over a wide area so that if the base vibrates, the field
> at the plinth magnets doesn't change much if at all. You can make it
> work
> but it's hard to make it as effective as cheaper alternatives.
>
> On the other hand, those cheaper alternatives ALSO require some careful
> engineering and they don't always get it. I can think of a mastering
> house
> in NYC that was having trouble with building vibration from the subway and
> installed a fancy isolated platform whose suspension had a resonance
> around
> 0.5 Hz which would get excited into wild motion by the subway....
> --scott
> --
at one time I sold Camera that were mounted to electron scanning
microscopes
one I personal was involved with was the on in the botony building at
cornell university
the professors there told me that a bus driving 1/4 mile away cause so much
vibration to render the microscope useless
so the scope was mounted to a 12 foot by 12 foot 25 foot deep slab of
reinforced concrete
I sure there were more details about suspension and stuff but this is what
it takes to eliminate common vibrations from devices

William Sommerwerck wrote:

>Suspending something in a vacuum does not, in and of itself "prevent
>vibrations". Whoever wrote this promotional material has little practical
>understanding of physics.

I worked for about a year for a company that makes chambers, valves, and
pumps for the high vacuum industry and was amazed at the misconceptions
of many within the company concerning high vacuum. The best was the
assembly technician who confused vacuum and gravity and believed that
astronauts floated around as they do because they were in the vacuum of
space!

--
================================================== ======================
Michael Kesti | "And like, one and one don't make
| two, one and one make one."
mrkesti at hotmail dot com | - The Who, Bargain

"George's Pro Sound Company" > wrote in
message m
> "Scott Dorsey" > wrote in message
> ...

>> It is magnetically suspended. The vacuum will prevent
>> air currents from moving the plinth around. However,
>> the vacuum will also change the damping
>> of the cartridge somewhat,

Negligible if relevant, but the picture tells a different story. I recollect
that Scott's browser does not show pictures as easily as the ones most of us
use.

>> and I am not sure what it
>> will do to the record/stylus interface.

If you look at the picture, the plinth, the platter, the tone arm, and the
cartridge are out in the air. The evacuated chamber must be below the plinth
where we can't easily see it.

http://www.bornrich.org/entry/top-10...ve-turntables/

Item 5 - the Continuum Caliburn.

> but if the magnets vibrate would not the change in flux
> vector cause a vibration in the suspended object

George, you are so right. Magnetic suspension creates a force that varies,
depending on the distance between the magnet and the suspended object. If
the magnet moves closer to the object, then the force on the object
increases. Sort of like a spring.

Magnetic suspension's big advantage is reduced friction that would oppose
the rotation of the platter. It is used to create so-called 'frictionless"
bearings.

As a suspension that would resist or absorb vibration, magnetism shapes up
as just another combination of mass, spring, and damper.

William Sommerwerck wrote...

> Suspending something in a vacuum does not, in and of itself "prevent
> vibrations". Whoever wrote this promotional material has little practical
> understanding of physics.

It's the fault of whichever eedjit wrote the article for bornrich. He
appears to have confused the bearing design with the vacuum platter
clamping system.

Continuum themselves say...

"Other features include the use of a ball/thrust pad configuration for
vertical motion, and bronze alloy for the axial motion.

The bronze alloy contains higher than normal tin compounds, which fill
any micro asperities in the shaft over time to create an ultra silent
bearing.

We chose not to use magnetic vertical bearings as the VTA is constantly
changing due to the rotational effects of the platter, which results in
a loss of depth and soundstage."


The whole things rubbish, VPI will no doubt be surprised to learn that
they are now a subdivision of the Teac corp and that their HRX table
features 24 extremely, 300rpm AC synchronous motors, Or perhaps not.

I'm off to read the in depth reviews at
http://www.bornrich.org/entry/top-10...everyone-cant-
afford/

--
Ken
http://www.members.lycos.co.uk/buddyduck/

George's Pro Sound Company > wrote:
>at one time I sold Camera that were mounted to electron scanning
>microscopes
>one I personal was involved with was the on in the botony building at
>cornell university
>the professors there told me that a bus driving 1/4 mile away cause so much
>vibration to render the microscope useless
>so the scope was mounted to a 12 foot by 12 foot 25 foot deep slab of
>reinforced concrete

This is normal. Mass is your friend. I have a small slab poured here
which is isolated from the rest of the building foundation and has the
lathe and turntable mounted on it. It's only a fraction of that size
but it seems to do pretty well.

>I sure there were more details about suspension and stuff but this is what
>it takes to eliminate common vibrations from devices

The lower the frequency, the more mass it takes.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."