Hi. I am a bit concerned with whether or not a cartridge that is being sent to me will match well with a tonearm another fellow sent to me as an upgrade for my Micro Seiki BL-51.
The cartridge in question is a Shelter 201. According to the specs, it weighs 6.2-grams, and has a compliance of 15-10 @ 100hz. I figure that this means that it is around 26-10 @ 10hz.
The tonearm in question is a Micro Seiki MA-101 MKII, which is reputed to have an affective armtube mass of 7-grams. In addition, I found a wood headshell that weighs 7-grams as well. Should this not give me a total affective mass of around 12-grams?
Using the best compliance calculator that I can find online (korfaudio.com), it looks like a good match. The "old fashioned" calculator at Vinyl Engine say it isn't, but I have found it to be pretty inaccurate compared to my real-world findings so far.
How many of you have used this cartridge, and what tonearms and headshells have you successfully used with it?
The cartridge in question is a Shelter 201. According to the specs, it weighs 6.2-grams, and has a compliance of 15-10 @ 100hz. I figure that this means that it is around 26-10 @ 10hz.
The tonearm in question is a Micro Seiki MA-101 MKII, which is reputed to have an affective armtube mass of 7-grams. In addition, I found a wood headshell that weighs 7-grams as well. Should this not give me a total affective mass of around 12-grams?
Using the best compliance calculator that I can find online (korfaudio.com), it looks like a good match. The "old fashioned" calculator at Vinyl Engine say it isn't, but I have found it to be pretty inaccurate compared to my real-world findings so far.
How many of you have used this cartridge, and what tonearms and headshells have you successfully used with it?
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Effective mass is the total of arm, headshell and cartridge, you seem to have miscalculated this...
Just to clarify compliance values used to be given in 10^-6 cm/dyne units, which is very confusing (sometimes seen as µcm/dyne). In SI units this translates to mm/N. So for instance 12 means 12mm/N. Compliance is simply the reciprocal of spring-constant, so is measured in m/N (spring constant is N/m)
To calculate its easier to convert to stiffness (spring constant), so for instance 12mm/N is ~ 83N/m. To calculate resonant frequency the formula is 1/2π x sqrt(stiffness/mass) in S.I. units, so here:
effective mass = 7g + 6.2g + 7g = 20g = 0.02kg, so f = 1/2π √(83/0.02) ~= 10Hz. (if compliance is 12 mm/N)
You want the resonant frequency of the arm to be well below 20Hz so its not activated by the audio signal. However you can't just add more mass as the cantilevel can bottom-out on a warped record or lowering the stylus into the groove quickly. Also the cantilever suspension damping becomes less effective with more mass to control.
I think a more informative measurement would be the impulse response of the arm to a small step-change in force, as that would show the degree of damping as well as resonant frequency, although this is hard to do, but its how suspension in a vehicle is evaluated (its the exact same physics).
BTW I've also seen compliance units of µm/mN which is not a valid S.I. unit as only one prefix multiplier is allowed, in order keep things as simple as possible. So mm/N is the unit to use for sane calculation I suggest.
Just to clarify compliance values used to be given in 10^-6 cm/dyne units, which is very confusing (sometimes seen as µcm/dyne). In SI units this translates to mm/N. So for instance 12 means 12mm/N. Compliance is simply the reciprocal of spring-constant, so is measured in m/N (spring constant is N/m)
To calculate its easier to convert to stiffness (spring constant), so for instance 12mm/N is ~ 83N/m. To calculate resonant frequency the formula is 1/2π x sqrt(stiffness/mass) in S.I. units, so here:
effective mass = 7g + 6.2g + 7g = 20g = 0.02kg, so f = 1/2π √(83/0.02) ~= 10Hz. (if compliance is 12 mm/N)
You want the resonant frequency of the arm to be well below 20Hz so its not activated by the audio signal. However you can't just add more mass as the cantilevel can bottom-out on a warped record or lowering the stylus into the groove quickly. Also the cantilever suspension damping becomes less effective with more mass to control.
I think a more informative measurement would be the impulse response of the arm to a small step-change in force, as that would show the degree of damping as well as resonant frequency, although this is hard to do, but its how suspension in a vehicle is evaluated (its the exact same physics).
BTW I've also seen compliance units of µm/mN which is not a valid S.I. unit as only one prefix multiplier is allowed, in order keep things as simple as possible. So mm/N is the unit to use for sane calculation I suggest.
Mark. You are not right regarding the effective mass. It is not this simple. The effective mass means the mass placed at the stylus point that will give the same inertia (around the pivot point) as that of all the masses. Counterweight, pickup, headshell and the arm itself.
The arm effective mass should include everything in the arm - if it includes the headshell you'd have to adjust the value when changing the headshell, if it doesn't you add that on. The headshell and cartridge masses are used as-is as they are at the radius-of-interest, the arm effective mass is actually its moment of inertia divided by the radius-of-interest squared. MoI is simply the sum of mr^2 for all masses m at radiuses r
However its true its not really clear what is meant by "an affective armtube mass of 7-grams." I'd assume its just the arm and counterweight assembly without headshell, but its an assumption...
However its true its not really clear what is meant by "an affective armtube mass of 7-grams." I'd assume its just the arm and counterweight assembly without headshell, but its an assumption...
After reading all of the available posts on the cartridge, I found that someone was using it successfully on a Rega tonearm that is roughly the same affective mass as the 101 + headshell.
I have revised my cartridge compliance findings to be around 21 @ 10-6, which brings me closer to an optimum match (8hz).
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It is always better to measure than calculate or guessing. Most test discs contain a resonance track (or two: one for the more critical vertical and one for horizontal). The test tones are usually in 2 Hz steps, you can easily see the peak vibration and hear the wobble sound. 8 to 12 Hz is the common target. If you measure too high, you can use a shim at the headshell. If too low, you can replace the counterweight and set the tracking force again.