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I know this is not a highly regarded arm but it's all I have right now. I'd like to know the effective mass of the TP13 and/or TP13A so I can do some math and decide what cartridge to get.
Thanks!
Follow Ups:
Actually, there is a fairly simple way to *estimate* the effective mass of your tonearm. You will need a small scale (a "dieter's scale" will suffice), a ruler calibrated in mm/cm and a calculator. Let me know, via email, if you are interested and I'll send you the details.
Well, I'm new here, and I wasn't sure if everyone (or _anyone_) was interested in the "tech side" of things.At any rate, this is a fairly simple way to *estimate* (i.e., there are more elaborate methods that will give more accurate results)effective mass that should be within in the means of most DIY type hobbyists. Remember, this is but one approach to the issue.
To keep things simple and easy, secure a cartridge of known weight (mass) to your headshell. Next, "zero balance" the tonearm. Next measure the distance from the pivot to the center of the counterweight. Then measure the distance from the pivot to the stylus tip (or, you may glean this from the tonearm's spec list). Next, remove and weigh the headshell and counterweight (_seperately_, of course!).
Now, to calculate the effective mass of the arm:
Mass of cart+headshell X (distance to the pivot-squared)
plus
Mass of counterweight X (distance to the pivot-squared)
equals
the moment of inertia (in g cm-squared), which, when divided by the square of the distance to the pivot, yeilds the effective mass.As an example, if we have an arm with a 20cm stylus-to-pivot dimension and a cartridge headshell mass of 10g, along with a counterweight weighing 100g, 2cm from the pivot (nice, round numbers), we have this:
10g X 20cm-squared + 100g X 2cm-squared
*or*
10 x 400 = 4000 plus 100 X 4 = 400so, 4000 + 400 = 4400
Therefore, the moment of enertia is: 4400g cm-squared
The moment of inertia (4400g cm-squared) is then divided by 20cm-squared (the square of the distance to the pivot), giving an effective mass of 11 grams.
I hope this all makes sense and I apologize for not having the appropriate notation available on my keyboard.
The only concern I have is that you probably should add some additional effective mass to account for the mass of the arm, itself. A good estimate might be about one third of what you believe the arm’s mass to be. In other words, if you think the arm weighs 9g, you should add 3g to the effective mass. For your example, this would increase the effective mass from 11g to 14g.Also, remember that this figure represents the effective mass for the arm-with-cartridge and not simply the arm, alone. You must subtract the mass of the cartridge to obtain the tonearm’s effective mass.
Thanks, Auxarcs, and welcome to the Asylum.
Best regards,
John Elison
Yes, one _can_ make additional allowances for the (varying from arm to arm) mass of the arm tube, but, as I said this was a simplified method. Also, IMO, the mass and position of the counterweight tends to be indicative, to an extent, of arm tube mass differences between otherwise similar arms, and that is reflected in the final figures.
Yes, the method I gave does include the mass with the chosen (known weight) cartridge. I included a cartridge to ensure the ability to "zero balance" the arm, so as to get an accurate fix on the position of the counterweight. So, if one wants the mass of the arm sans a cartridge, remove the weight of the cartridge from the headshell prior to doing the math.
I hope folks find this helpful, and thanks for the welcome, John.
I don't think that anyone can give you data about the 'mass' of the old TP13 arm, not that you calculate what cartridge you can choose for it with 'some math'. The TP13 is a good high mass arm, fit a good heavy cartridge and it will work fine. 'Heavy' does not mean 'bad': under this label you can put the old Ortofon SPUs and the early EMT TSD-series, so you have plenty to choose.Stefano
Thanks for the advice Stefano. I was under the impression that there were specs like mass etc available for most arms. Anyways, I will check a few shops tomorrow for heavy carts.
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