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Re: Except....

Posted by John Gratsias (A) on June 16, 2005 at 19:08:55

In Reply to: Except.... posted by Mark Kelly on June 15, 2005 at 20:56:07:

> I would like to be able to say that no Hi Fi manufacturer would
> stay in business with scientific instrument pricing, but.....

...but the audio manufacturers have outdone themselves offering ludicrous engineering at stratospheric prices.

> What I mean to say is that unless a turntable is built to
> instrument standards then the decoupling solutions applicable
> to instrumentation are probably not going to be the entire answer
> because they don't address the problems of internally generated vibration.

I don't agree with this; AFMs use translating and rotating stages, so they encounter the same internally generating noise. Certainly, the vibrations produced by these stages are a lot lower in amplitude than the ones generated by a 33rpm spinning platter, but then again an AFM needs to have a resolution 5 orders of magnitude higher than what turntables need.

There simply is no engineering reason for the sub-standard products audio manufacturers promote -- it's just ignorance and the entrenched dynamics of a niche, uninformed, segment of the market.

> While I've got you John, can you tell me if there is a simple rule
> of thumb for the ratio between the minimum speed which gives
> adequate lift and the maximum sustainable speed for a hydrodynamic bearing?

I'm not qualified enough to offer a definitive answer, but from what I've seen the details of the design are critically important, thus precluding a simple rule of thumb. I've asked some of the experts around here, and they've told me that for such low rpm applications (33 or 45), air bearings would be my best option, although most of them thought that a well designed sleeve bearing could work very well.

John

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