Structure- and air-borne vibration in turntables

andy19191 · 9th June 2006, 01:46 PM

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.

9th June 2006, 01:46 PM	#1
andy19191 diyAudio Member Join Date: Apr 2005 Location: -	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.

10th June 2006, 07:00 PM	#2
EC8010 diyAudio Moderator Emeritus Join Date: Jan 2003 Location: Near London. UK	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? __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

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10th June 2006, 07:39 PM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

10th June 2006, 08:04 PM	#4
audio-kraut diyAudio Member Join Date: Apr 2004 Location: 12km off the alaska highway in northern BC	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.

11th June 2006, 10:25 AM	#5
andy19191 diyAudio Member Join Date: Apr 2005 Location: -	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.