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Old 3rd April 2006, 01:54 PM   #21
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Quote:
This will easily be in the 50 -100g range. (I recall having read about a Ladegarrd arm loaded with several 100g of additional mass). On poorly centered records, such a heavy mass will make the stylus cantivlever flop back and forth with a large amplitude
among my over 1500 LP's I have none that would cause the linear arm to behave in such a matter. I think this concern is overrated.
The mass of the MG1 arm for instance is very low, as the bearing consists of a piece of very thin aluminum tube, and the arm itslf is very light plastic.

Quote:
1.Low mass slide arm tube for only 25 gram without cartridge and counter weight.
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Old 3rd April 2006, 03:52 PM   #22
baggins is offline baggins  United Kingdom
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Could one not build a reasonably low friction bearing tube assembly
and then just adjust it angularely (sic) to overcome any remaining friction. i.e. give the cartridge arm a slight bias towards falling to the centre of the record The cartridge compliance would then only have to keep it centered so to speak.
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Old 3rd April 2006, 05:24 PM   #23
soeren is offline soeren  Greenland
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Default moving mass

There seems to be a little confusion about the moving mass and how the ideal arm should be. The criterias for Poul Ladegaard are among other things, that you should be able to control the mass independently vertically and horizotally so that:

- the vertical resonance is just under what we want to reproduce, typically 15 to 20 Hz. It should by all means be over 5-7 Hz as the pressing errors (warp) have a maximum there. This means practically a very short arm, which thus has to be tangential.

- the horizontal frequency should for best bass transients be very low, it should only be considerably over half a Hertz as an eccentric record has that frequency. He proposes 3 Hz as a good beginning and that means adding some mass, very depending on the cardrigde. The advantage of the Ladegaard arm is outsides its extreme simplicity that it is very easy to adjust for individual cardrigdes.

He finds himself, that the biggest problem with it is that he has not found a good way of damping it, limiting the air flow is too dangerous, but I can see, that some of you thought as me, that it should be made by some kind of liquid damping.

I have discussed these and other problems with him, we both wrote for the same danish audio magazine, and personally I think that the reason that these airborne arms are sounding so good also is due to the phenomen that when the wave runs down the arm tube itself, then it will not meet a mechanical mirror in form of a bearing, which will send the wave back. This is a medium/treble problem. Ladegaard agrees that it could be an important part of the explanation. Thus the interest in the damping of the tube and counterweight suspension.

Søren
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Old 3rd April 2006, 05:41 PM   #24
pixpop is offline pixpop  United States
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Quote:
This one might also be quite easy to make: Opus 3 Cantus
Wow, that's beautiful How does it work? Hard to tell from the picture. Can anyone translate the text?
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Old 3rd April 2006, 05:48 PM   #25
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Another opus picture
Click the image to open in full size.
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Old 3rd April 2006, 06:04 PM   #26
pixpop is offline pixpop  United States
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What's inside the tube?
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Old 3rd April 2006, 08:10 PM   #27
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Default Sound waves reflection and arm damping

Quote:
when the wave runs down the arm tube itself, then it will not meet a mechanical mirror in form of a bearing, which will send the wave back.
When the sound wave propagading through certain media, meets the boundary surface of the material, it is partly reflected back, and the reflected wave amplitude and phase shift is depending on properties of two contacted materials , like density, boundary shape and damping factors. Generally, the more dissimilar the contacted materials are, the more LF energy is bounced back (to stylus!), causing muddy bass. That's why the metal bearing arm usually have better bass resolution, comparing to air bearings. The metal bearing arms require less armtube damping, because direct metal-to-metal contact provides good path for LF vibrations to be absorbed "downstream".
The Schreder style arm has similar problem, that's why herr Schreder pays so much attention to the armtube material choise. I believe hardwood has some important advantage here, call it "sonic signature", which means the whole stylus-induced vibrations frequency band is being absorbed/reflected more evenly, causing less severe resonant peaks and cancellations.
Do not get me wrong, I think the air bearing tangential arm (and the Ladegaard design specifically) is a brilliant idea, and I like my Ladegaard clone very much. But it is important to clearly understand its weak point to address it. I'm going to try some sort of oil impregnated hardwood armtube and see how it helps to improve (or or not) the sonic. Will report back.
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Old 4th April 2006, 05:43 AM   #28
harhaug is offline harhaug  Norway
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Quote:
Originally posted by audio-kraut


among my over 1500 LP's I have none that would cause the linear arm to behave in such a matter. I think this concern is overrated.
The mass of the MG1 arm for instance is very low, as the bearing consists of a piece of very thin aluminum tube, and the arm itslf is very light plastic.

Quote:
1.Low mass slide arm tube for only 25 gram without cartridge and counter weight.
When you add the mass of the counterweight and the cartridge you easily get an additional 25 g.

I'll dig up my calculations regarding the additional displacement of the stylus due to eccentric records. Now, a calculation is one thing - audible effects is another.

- Harald
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Old 4th April 2006, 03:14 PM   #29
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One way to impregnate some timber with oil....

Submerge the piece of wood in a vacuum chamber, cover with oil and pull a vacuum. Leave overnight. Air/moisture gets sucked out of the wood and cavities are filled by the oil. Best to use an oil which will harden like danish oil.... otherwise you will have oil leaching back out of the timber with changes in temperature.


Fran
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Old 4th April 2006, 03:30 PM   #30
tinitus is offline tinitus  Europe
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Some years ago I used a similar homemade tangential airsupported tonearm
Only real problem was noisy and "pumping" airsupply

Should I make one today I would consider some form of small compressor with a tank big anough to supply air without any motor running

You then can adjust a precise amount of pressure and get a fluid supply of air without noise and "pumping"

Maybe you couold use a compressor from a old refrigerator

Anyway there should some form of "buffer"
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