Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Pinging DICE 45--Diy tonearm question?
Pinging DICE 45--Diy tonearm question?
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 27th November 2002, 06:58 PM   #1
hard times is offline hard times
diyAudio Member
Join Date: Aug 2002
Location: CA
Default Pinging DICE 45--Diy tonearm question?

Dice 45, first I'd like to thank you for rousing up my interest in making a unipivot tonearm. I read some of the posts down below this one. I've used some ideas from the Altmann arm plus most of what you recommended. I'm 99.8% finished my 12"white oak arm, and have mounted a junkish cartridge just to be amazed at how stable and smoothly this thing appears to track.
My question to you is, by what method can the arm mass be determined so as to decide in what compliance range my "real"(not purchased yet) cart will be. It can't be as simple as weighing it, or choosing a "mid" compliance and go from there right?
I think I am looking for the "rotational" mass as the arm tracks the groove, etc. Please keep in mind that I am just a technician-type lacking the exposure to the physics behind the correct answer. Thanks for any tips and help!
  Reply With Quote
Old 27th November 2002, 07:02 PM   #2
peranders is offline peranders  Sweden
Electrons are yellow and more is better!
diyAudio Member
peranders's Avatar
Join Date: Apr 2002
Location: Göteborg, Sweden
Pinging DICE 45--Diy tonearm question?
I have nothing to add here technically but I'm very interested in how your tonearm look like. Do you have any pictures?
/Per-Anders (my first name) or P-A as my friends call me
Group buy: DCT03 DC trap for big toroidal transformers. Sign up for interest HERE. 41 pcb's in interest.
  Reply With Quote
Old 28th November 2002, 12:50 AM   #3
fdegrove is offline fdegrove  Europe
diyAudio Senior Member
fdegrove's Avatar
Join Date: Aug 2002
Location: Belgium


Since it is made out of wood which is medium weight as far as most tonearms go (unless you use balsa) it seems to me a low to medium compliance cartridge would work fine.

by what method can the arm mass be determined so as to decide in what compliance range my "real"(not purchased yet) cart will be.
The arm mass is determined by its' moving parts so in your case the armtube/headshell and counterweights assembly.
I can't remember the rough breakdown figures putting one type in one class or the other but Dice45 might.

  Reply With Quote
Old 28th November 2002, 06:51 PM   #4
dice45 is offline dice45  Germany
diyAudio Member
Join Date: Jan 2002
Location: Munich, Bavaria
hard times,
thank you.
your simple Q is hard to answer. Takes extended homework. My diagram is too small to post, have to redraw it with CAD help to a usable size.
Too tired this evening, i come back later with details.

Possible procedures:
You have a soft helical spring with a known spring constant. You apply the string to the tonearm at the radius the stylus would be. Then you move it up and down with different frequency and find the systems natural resonance frequency. From that frequency and the known spring constant you calculate the rotational inertia in reference to the tonearm's horizontal pivot axis. And jconvert that inertia to a virtual mass located at stylus radius.
You also can assume with sufficient precision this as a translational problem and use the formula for a mass hanging on a spring:
f= (1/2*pi)*sqrt(c/m) with f being frequency, c being spring constant and m being the effective mass. Solve that equation for m.

You can take an unknown cartridge an mount it into a tonearm of known effective mass. You measure the frequency (use a test record). Solve the equation above for c. c is the cartridge compliance.

Then mount this cartridge into your new tonearm and measure the frequency, from that and from the formula above solved for m you can calculate your new tonearms effective mass.

1b) and 2) is easier if you have that durned diagram, giving a family of curves with c as parameter, effective mass as Y-axis and frequnecy as X-axis.

make a 3D model of your tonearm and integrate about all infinitesimal mass points, each having a densitiy attached and calculate the total inertia in reference to the horizontal pivot. Like 1a). This gives you the "effective mass" with highest precision. Better use a highend CAD for that and tell me when you are ready, i marry your girl and get old with her in the meantime i just mentioned it for completeness' sake.
Expect horizontal and vertical effective mass to be almost the same for a pivoted tonearm.

I see when i can bring the diagram.
  Reply With Quote
Old 28th November 2002, 07:05 PM   #5
Havoc is offline Havoc
diyAudio Member
Join Date: Feb 2002
Location: Belgium
In my case I guess I have it done in CAD before I find a cartridge and an arm

Even if you take into account that I'm now off installing W2K again.
  Reply With Quote
Old 22nd January 2003, 02:40 AM   #6
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
EC8010's Avatar
Join Date: Jan 2003
Location: Near London. UK
Default Effective mass

The "effective mass" of the arm has little to do with the actual mass of the arm. It's all about inertia, which is proportional to the square of distance of masses from the pivot. Thus, a heavier counterweight actually reduces mass because its counterbalancing force (the moment) is proportional only to the distance. That's why arms have big, heavy counterweights close to their pivot.

To return to your question. Because effective mass is determined by the square of distance, only the headshell mass is really significant. As a huge generalisation, unless your arm is a spindly little thing with holes drilled everywhere, it would probably prefer to see a moving coil cartridge. One-piece arms like the Rega are lower mass than you might expect because the lack of joints (particularly at the headshell) greatly reduces effective mass.
  Reply With Quote
Old 22nd December 2003, 05:06 PM   #7
perfusionist is offline perfusionist  United States
diyAudio Member
Join Date: Oct 2003
Location: Tejas
Default Ping EC8010

Ping EC8010

I want to figure the lowest amout of actual mass in a 12" tonearm to acheive 4.7 grams effective mass. Can a small shifting weight about the center axis be used to alter effective mass? The cartridge weighs 6.3 grams. I have calculated that with my compliance of 25cm/dyne, to get the resonance to 10 hz, I need 10 grams effective mass. The SME SeriesIII improved has a resonance of 10Hz with the same cartridge. It has an effective mass of 6.1 grams. I wonder if it can be made lighter, and still keep the same effective lateral mass, and how. Are there any formulas for this. To figure the effective mass, I used this formula Resonance 10 = 1000 * 6.28 sqrt (cartridge mass +effective mass) HELP
  Reply With Quote


Pinging DICE 45--Diy tonearm question?Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Newbie DIY tonearm question 60goldtop Analogue Source 6 23rd July 2009 06:05 PM
SME 3009 Tonearm Question radio2head Analogue Source 4 16th February 2009 11:34 AM
Sweet Jesus !!! Another F3 ! (56K ? No dice !) lordvader Pass Labs 27 24th September 2008 09:23 PM
Fuzzy dice and bongos, fuzzy dice... andy_c Music 6 12th February 2004 03:47 AM
Congrats Dice Penguin Analogue Source 13 27th October 2002 02:57 PM

New To Site? Need Help?

All times are GMT. The time now is 04:15 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio