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Old 29th May 2004, 10:08 AM   #11
sreten is offline sreten  United Kingdom
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BrianL,

IMO your post did not answer the basic question, and your
electrical analogy of an RCR filter ignored than these are
used with a capacitive smoothed supply = a large tank.

sreten.
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Old 31st May 2004, 08:26 AM   #12
peterr is offline peterr  Netherlands
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Thank you all for your answers. I think I will try it both ways and see wich is best.

Meanwhile I have another question, this time about horizontal moving mass (a real snakepit it seems):

Poul Ladegaard states it can be (or even should be) quite high, in the order of 250gr, to get horizontal resonance frequency far down. In his paper he backs this up with measurements and facts.
Also Jeremy Epstein built his along these lines and I think I read somewhere that Dice45 believes this to be the best way too.

In other places I have read it should be as light as possible and that the higher horizontal moving mass is the biggest drawback of a linear tracking arm.

Any facts to shed some light?
Thanks.
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Old 31st May 2004, 08:48 AM   #13
sreten is offline sreten  United Kingdom
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http://www.diyaudio.com/forums/showt...091&highlight=

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Old 31st May 2004, 07:23 PM   #14
peterr is offline peterr  Netherlands
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thank you , I had missed that thread (wasn't looking for a new Nagaoka ).
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Old 31st May 2004, 07:48 PM   #15
fdegrove is offline fdegrove  Europe
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Hi,

The thing about linear arms is that the lateral mass actually IS your effective mass as they don't pivot.

It then follows that lateral mass is always higher than vertical mass as it is with pivoted arms.
Tangential arm design is a compromise between too-low vertical mass and too-high horizontal mass.

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Old 1st June 2004, 12:59 PM   #16
dice45 is offline dice45  Germany
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Default keep horizontal resonance above 4.5Hz

Peterr,

on a Ladegaard design, i would not panic concerning horizontal mass. If you can keep the horizontal resonance above say 4.5Hz, your arm will work fine.
Lateral run error frequency is 33rpm/60sec: 0.55Hz
So 4.5Hz is more than 3 octaves away: supercritical damping will give you a nice insulation from the run error's excitation.
Assumed the cartridge's compliance will be vertically and laterally equal and constant, resonance frequency increases with the square root of mass. And as the Ladegaard's slider is not adding to vertical effective mass, you can shove vertical and lateral resonance to desired frequencies, within limits of course.

After all, a Ladegaard slider is not be a heavy-weight component and a total lateral mass of 36gr without the counterweight (compare the AirTangent) should be within reach.

A higher lateral mass should lead to superior tracking provided the resonance is not too low.
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Old 1st June 2004, 04:21 PM   #17
sreten is offline sreten  United Kingdom
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Basically agree except for a couple of minor points.

Critical damping of the horizontal resonant frequency as far
as I can tell is not required. In fact Q doesn't really come into it.
Nor is critical damping of the vertical frequency particularly relevant.

Horizontal stylus deflection for moving the slide is related to
compliance only i.e. resonant frequency.
Scale the following graph down in frequency by x100, full scale = 10Hz.

Shown are two Q's for 4.5 Hz (one "critical"), also
1.5Hz, 3Hz and 6Hz, level at 0.55Hz (55Hz) matters.

What this shows is 4Hz to 5Hz is an excellent minimum
and as stated not difficult to achieve with correct mass.

sreten.
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Old 1st June 2004, 05:00 PM   #18
dice45 is offline dice45  Germany
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Default Supercritical damping

sreten,

i did not mean "critical" damping, adressing any possible Q, i meant super-critical damping:
Put the lowest interesting frequency way above the exciting frequency as the gain of the excitation transfer function is

unity below resonance,

way above unity (depending on Q) in proximity of and at the resonance and

way **below** unity above the resonance frequency (how much is again depending on Q).

This means that the excitation amplitude will be transferred with a gain of way below unity i.e. damped to a high extent.
It is the way most turntable suspensions work.
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Old 1st June 2004, 05:20 PM   #19
sreten is offline sreten  United Kingdom
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Default Re: Supercritical damping

Quote:
Originally posted by dice45
sreten,

i did not mean "critical" damping, adressing any possible Q, i meant super-critical damping:
Put the lowest interesting frequency way above the exciting frequency as the gain of the excitation transfer function is

unity below resonance,

way above unity (depending on Q) in proximity of and at the resonance and

way **below** unity above the resonance frequency (how much is again depending on Q).

This means that the excitation amplitude will be transferred with a gain of way below unity i.e. damped to a high extent.
It is the way most turntable suspensions work.
But as I've shown - damping (engineering definition) is not
the issue, that is Q is not relevant - you don't make sense.

"Critical" damping for a resonant system is explicitly defined,
so your "super-critical" definition is way off interpretable for
me, nevermind anyone else struggling to follow you.
There is no such thing in engineering terms.

You are quite correct my graphs with appropriate scaling are
applicable to turntables but "super-critical" is not relevant.

Unless you mean a Q of above critical, "super-critical"
is a totally a very poor way of describing this IMO.

sreten.
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Old 2nd June 2004, 06:42 PM   #20
dice45 is offline dice45  Germany
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sreten,


i am not an Englisch native speaker and in German engineering terms the crititical frequency is the frenquency at which the resonance peak, the so-called resonance catastrophe is happening (at zero damping/ infinte Q of course), hence the term "super-critical damping" for positioning the lowest interesting system frequency way above the critical frequency.

So, i don't make sense, huh?
I described exactly what i meant (i re-read my post) and you obviously enjoy to split hairs on technical terms
I do not enjoy that sort of fruitless discussion; i had way more than my share of it already (particularly here@diyAudio). Back to lurking mode. Bye.

Bernhard
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