DIY Schroeder Tonearm???

[bear]

Originally Posted by koldby

That link actually makes me wonder if some of the thoughts I had regarding vibrations, was not that far from the truth:
Reflections from the counterweight has to be dealt with, espeacially if there isn´t a ridig point along the arm tube. And yes a way to do that is to make the arm tube a lossy transmission line.
As far as I can see the rigid bearing CAN (not nessesary does) terminate to a certain degree the vibrations so you can transform the vibrations to heat outside the wand.

Please enlighten me if I am totally wrong here.

Koldby

A typical solution is to make a very lossy mount (rubber typically) for the counterweight...

_-_-bear

[Jeffrey Davison]

On my build, I used a principle called mass dampning. On the end stub, I used a short bronze rod suspended in an closed cell neoprene cylinder inserted in a thin wall titanium tube. The tube is capped with silicone plugs.
It is extremely effective at damping energies.

I have no means to actully make resonance measurements. But if you take a similar length and diameter solid rod as my stub, or a hollow tube the same length and diameter, and drop it from a given distance onto a solid surface, they will have a degree of "bounce" and "ringing". I also tried just the titanium tube with only the neoprene tube without the bronze rod..it had the same "bounce" and only slightly less "ringing"
But if you take my end stub with the bronze rod and drop it from the same distance, it exhibits practiacly no bounce at all with a very dull "thud"..no ringing or resononance, at least discernable by the ear.

Also the counter weight is solid copper, a very dense metal, and is decoupled with a delrin bushing.

The armwand itself is a multi-section affair. It has a thin walled titanium outer tube with a small diameter carbon fiber tube concentricly suspended along the inside length with small diameter Buna-N "O" rings that not only support the inner tube, but act as dampers as well.
In my 10.5 inch arm there are 10 "O" rings spaced along the length of the tube. If you look closely in one of the pictures with my "raw" parts, (even-tho I didn't use the outrigger counterweight eventually) you can see the carbon fiber rod "peeping" out of the arm tube.


Jeff Davison

[bear]

Jeffery, I saw your post earlier on this... seems like a nice solution... I expected to see the mass suspended on two ends... so I am wondering if the end pieces make any difference other than keeping it in place, and how different the performance might be without the mass and just the foam inside the tube?

_-_-bear

I forgot to ask what sort of mill and/or lathe did you use for this job - wondering that of all the other builders in the thread as well!

[Jeffrey Davison]

I used both Front Panel Express and eMacineshop.com. Alas, I don't have any mills or lathes readily at hand and no one too local to work with. Had to farm out my drawings.

The end pieces are not really used to keep the internals in place as they are a snug fit. I used the silicone endpiece plugs as an aesthetic part that happened to have damping properties as well.

I actually got the mass dampening idea watching Formula One.... A few years ago when Renault was winning the WDC, early in the season the front end of the car, in the nose, used mass dampening to stabilize the front better in corners from road surface vibrations ans F1 cars have very stiff suspension. The device was declared "illegal" when it was deemed to be an unfair advantage and a "moveable" device which was not allowed according to the sporting regulations.

Jeff

Originally Posted by bear

Jeffery, I saw your post earlier on this... seems like a nice solution... I expected to see the mass suspended on two ends... so I am wondering if the end pieces make any difference other than keeping it in place, and how different the performance might be without the mass and just the foam inside the tube?

_-_-bear

I forgot to ask what sort of mill and/or lathe did you use for this job - wondering that of all the other builders in the thread as well!

[Jeffrey Davison]

Here's a Wiki definition.....

Tuned mass damper - Wikipedia, the free encyclopedia

[velvetsunrise]

Hi, I used a very old Myford 7 Lathe for all the turned parts, including the ebony wand. The rest of the parts were made by hand, from scrap pieces of brass and ally.

Had a week or two to listen to it, and it does sound wonderful, the best sound i have ever had from vinyl.

The only thing i have changed from my initial parts is to remake the counterweight slightly heavier to place it nearer the pivot.

I found the most difficult part to make is the aluminium wand/upper magnet carrier, it was very tricky to get the hole for the suspension thread central and true, i guess i got lucky as it came out fine the first time. With the lightweight version, i had to remake this piece twice.

The other difficult part was carving and shaping the headshell end of the wand for the cartridge, also fileing out the slots for the cartridge mounting, but i was determined to make the headshell/wand in one piece.

Overall i am extremely happy with it, so happy infact, i have started making a lightweight version to fit on my suspended sub chassis turntable.

[AuroraB]

Jeffrey - very nice , indeed...

Just wondering- what's the dia of the titanium tube?
and thinking out loud- would there be any benefit in using somthing softer than the closed cell foam....?

[Jeffrey Davison]

The diameter of the arm tube is .375". The Diameter of the end stub is .500"
I really didn't look further than the neoprene foam. I don't know if there is anything softer that is readily available... But the neoprene was an off the shelf solution that worked well in my experiments. True, that the assembly isn't really "tuned" as a true "Tuned mas dampner", but the principle works well enough for my arm.

Maybe Frank could adapt it and come up with a truely tuned mass damper for the toneatm counterweight end stub.... maybe even patent it ;^)


Jeff

Originally Posted by AuroraB

Jeffrey - very nice , indeed...

Just wondering- what's the dia of the titanium tube?
and thinking out loud- would there be any benefit in using somthing softer than the closed cell foam....?

[EC8010]

Originally Posted by berlinta

When measuring the lowest torsional mode on many tonearms, you'll find it to be between 300 and 500Hz. Normal modes(the fundamental) can be found from 1,3khz to 2,5kHz (up to 6kHz on the "stiffest" armwands I've measured).

That's very interesting data, and suggests to me that conventional wisdom of choosing the stiffest/lightest material in order to push the resonances up in frequency works against us, and that it's better leave the resonances below 500Hz and damp them if possible. Was that your thinking in your choice of wood?

The mass damping idea espoused later in this thread is fascinating. I've just bought another milling machine (not got it reassembled yet), but I can feel all sorts of project ideas coming on.

[nicoch58]

nice link Jeffrey !

the sublink too .... Stockbridge damper - Wikipedia, the free encyclopedia