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-   -   Structure- and air-borne vibration in turntables (http://www.diyaudio.com/forums/analogue-source/81167-structure-air-borne-vibration-turntables.html)

andy19191 9th June 2006 01:46 PM

Structure- and air-borne vibration in turntables
 
I am looking for information on the effectiveness of various approaches to minimising structure-borne and air-borne vibration in turntables. So far, I have turned up little of substance on the web and was hoping one or two here may have a few useful pointers. Many thanks.

EC8010 10th June 2006 07:00 PM

I suspect nobody has actually measured it. In theory, a suspended sub-chassis turntable behaves as a high-pass filter above its resonant frequency (usually tuned to 5Hz). Turntables like the AR XB1, Thorens TD150, Linn LP12 etc used this technique. It's awkward cueing on such a turntable.

The currently fashionable technique is to have a platter that weighs so much that sheer inertia prevents structure-borne vibration. Platters upwards of 20kg are not uncommon. They're also heavy on the wallet.

Doing anything about air-borne vibration would require enclosing the turntable in a sound-proof box. Another room, perhaps?

anatech 10th June 2006 07:39 PM

Hi EC8010,
There are some platter mats that "bond" with the LP to make it part of the overall rotating mass. I still have a "platter matter" that does that. You have to peel it off the record when you are done. I use mine on a Thorens.

-Chris

audio-kraut 10th June 2006 08:04 PM

works with non suspension tt's very well:

laminated plate (1/8 steel glued to 1/2" mdf in the centre) to have a "dead" base, float the base on an innertube - app. 12 - 16" diameter.
Works very well on my transcriptors hydraulic.

Also - found that having the cover down on the tt during playback greatly increases resonance from the ls. Easy to test. So no covers on my TT's.

andy19191 11th June 2006 10:25 AM

Thanks for the responses.

> I suspect nobody has actually measured it.

It is not difficult to determine by a variety of approaches. For example, the simplest is simply to play something through the speakers while a record is spinning in a silent groove and to listen to the phono output.

> In theory, a suspended sub-chassis turntable behaves as a high-pass filter
> above its resonant frequency (usually tuned to 5Hz). Turntables like the AR
> XB1, Thorens TD150, Linn LP12 etc used this technique. It's awkward cueing on
> such a turntable.

I have had no problem cueing on such turntables but banging about on sprung floors does cause problems. I do have a unipivot with a badly designed cueing mechanism which is awkward to cue.

> The currently fashionable technique is to have a platter that weighs so much
> that sheer inertia prevents structure-borne vibration. Platters upwards of 20kg
> are not uncommon. They're also heavy on the wallet.

Mass in itself has no direct effect on vibration isolation (but can in combination with stiffness, damping and other properties) although, of course, it can help even out an uneven driving motor.

> Doing anything about air-borne vibration would require enclosing the turntable
> in a sound-proof box.

That would be the simplest approach but it is rarely if ever done. Why not? Is air borne vibration so small as to be irrelevant?

> Another room, perhaps?

Somewhat impractical except for experiments.

> There are some platter mats that "bond" with the LP to make it part of the
> overall rotating mass. I still have a "platter matter" that does that. You have
> to peel it off the record when you are done.

If the platter is vibrating then is bonding to it wise? If the record is vibrating from air borne sound (it has a large area) and/or from structure borne sound from the stylus then is a strong bond what is required?.

> Also - found that having the cover down on the tt during playback greatly
> increases resonance from the ls. Easy to test. So no covers on my TT's.

What is the ls?

Thanks again for the responses but I was really after some numbers to quantify the phenomena mentioned above.


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