Tone arm effective mass

[jan.didden]

Hi,

I was wondering about tone arm effective mass issues and how that relates to a tangential arm.
(Note that I am a meter reader not a thread tapper ;-)
In this thread: http://www.diyaudio.com/forums/analogue-source/77390-effective-pick-up-arm-mass.html a spreadsheet is given to calculate the effective mass both in vertical and horizontal direction for a regular tone arm, based on arm geometry, weights etc.
This is a very usefull spreadsheet which works like a charm.

But if you use a tangential arm, how do you calculate effective mass?
At any rate, since the real mass and dimensions are much, much smaller, I would expect the effective mass also to be relatively small.
How does that effect selecting a cartridge (cartridge compliance)?

thanks for any advice,

jan didden

 

[DF96]

You would still need to get the arm-cartridge resonance to sit in the gap between warps and music. I guess this would mean a particularly high compliance cartridge, but as many were too high anyway (for many popular arms) this might not be a problem.

 

[jan.didden]

Thanks Doug; am I correct that a radial arm (the moving sleeve or sled or whatever) would have a (much) lower effective mass than a regular tangential arm?

jan

 

[Groove T]

Depends on execution of tangential arm.
Air beared ones have a vertical fres comparable to a radial arm, but the hor fres would be much lower due very high bearing mass. Sometimes they 2 differnet fres hor depending on construction.
Short arms like Souther/Clearaudio the fres hor and vert are pretty much the same, here the cartridge body weight makes the difference bigger. The tuning of the fres vert can be done with additional weights and counterweights to be in the area of 11hz.
For short arms thats very important to track with warped records. warped records produce here noticable changes in speed and the brightness due the vta changes.

 

[dtut]

I'm a little reluctant to chime in here because I'm just not sure, but I believe the horizontal eff. mass of a tangent arm equals the mass of all the moving parts of the arm, since it translates rather than pivots, and the vertical eff. mass can be calculated and is considerably less.

Roscoe Primrose discusses arm mass in his version of the Ladegaard air bearing.

Poul Ladegaard's Air Bearing Tangential Tonearm Page

I've gotten good results from various high compliance Shure carts in a roller bearing tangent arm. Reducing mass as much as possible made a definite improvement.

Hope this is helpful.

 

[jan.didden]

Thanks guys; I'm starting to get It

One implementation I was looking at is the attached, but I don't have detailed specs.

 

[kevinkr]

Jan,
Take a look at the Opus 3 Cantus Parallel Tracking arm thread here: http://www.diyaudio.com/forums/analogue-source/34126-opus-3-cantus-parallel-tracking-arm.html

You might find this design of interest as well.

 

[dtut]

Jan,

Thanks for that link - it actually works in NeoOffice on my Mac.

What does "slider weight - the part that doesn't effect vertical eff. mass" mean? The only thing I can think of is the bearings and their housing and, with any luck, that doesn't slide.

 

[jan.didden]

I think it is actually called the sleeve - it's the gold-colored sleeve in the picture that slides across the tangential arm.
It doesn't pivot of course but translates horizontally so its weight is the effective weight.

jan

 

[MiiB]

one thing that strikes me on that Arm design is the placement of the horizontal pivoting axis. While the short arm may be desirable in terms of mass and flexing then the drawback is that the pivot axis must be placed quite a bit above the stylus, this this translates into speed changes on every warp on the record....

But I guess You can't win them all...

 

[jan.didden]

Yes. There are also tangential arms that actually has a short arm so that the tangential tube can be placed outside the turntable perimeter and lower, making the vertical pivot point level with the record surface.

jan

 

[dtut]

Jan,

Thanks. "Slider" = "sleeve."

I just revisited that program. I wasn't really paying attention the first time so when I looked the second time - understanding "slider" this time - the light came on. I've been building linear trackers for a couple of years, but effective mass and, especially, resonant frequencies have been nearly complete unknowns to me. I hope this program is accurate because I want to start plugging in numbers immediately. And once I have some answers, maybe that will push me to do some measurements.

There have been some real advances made for DIY LTs - check out the link Kevin posted - but numbers and measurements just aren't there, yet.

 

[AVWERK]

Janneman
That arm you posted looks like a real contender...
Very similiar to the Air Tangent in operation

Do you have any more info on this?

Regards
David

 

[jan.didden]

There's a thread on this stuff in Vendors Bazaar here: http://www.diyaudio.com/forums/vend...n-audio-high-quality-turntables-tonearms.html

I'm just at this time looking to upgrade my LP replay system and as you say these look very good.
What makes me hesitate is that I cannot find any more tech info, like effective tone arm mass to determine whether I should use it with a high- or low compliance cartridge, or the noise production of that pump.
So if anybody does have that info, I'd like to hear it!

jan