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On Effective Mass and Cartridge Matching

General Principles

  • A good way to visualize cartridge to tonearm matching is to consider how springs and shock absorbers to an automobile’s weight.  You would no sooner install shocks and springs designed for a Porsche onto a pickup truck, then you would do the reverse.
  • In the same way , you want to select a cartridge whose compliance (spring stiffness) mates well with the effective mass of your tonearm.
  • Cartridges’ suspensions have varying stiffness and this is what is referred to as compliance – normally stated as an expnentiated number like  12 * 10 <-6 (12 times 10 to the minus 6th power or .000012).
  • The cartridge’s compliance, in conjunction with all of the mass that the suspension is “attached” to forms a resonant circuit.  These masses are comprised of the effective mass of the tonearm and the weight (or mass) of the cartridge.
  • The rule of thumb is to try for a combination that nets a resonant frequency in the 10-12 Hz range.
  • We have found that shifting the resonant frequency by as little as .2Hz can have a dramatic effect (more on how we did this, below).
  • The good news about all of this is that most modern cartridges are designed around the effective mass of todays’ modern tonearms, so you’ll have generally good compatibility.
  • Vintage cartridges (i.e. Ortofon SPU) and many modern mono cartridges have low compliance (stiff suspensions) and work best with higher mass tonearms.
  • Tracking forces tend to relate to a cartridge’s compliance, with low compliance (stiff suspension) cartridges tending toward higher tracking forces (3-4 grams), medium compliance cartridges (most modern moving coils) tending toward medium tracking forces (1.8 to 2.2 grams), and high compliance cartridges like Shure moving magnets working with about 1.0 gram tracking force.
  • Given that we’ve found minor changes in effective mass can produce subtle but yet profound changes, the best way to cartridge selection for you tonearm is to consult as many individual as you can – to get a consensus ideal combinations.

Tonearms With Multiple Counterweights

Some tonearms (Moerch, Durand, Tri-Planar, etc.) have multiple counterweights.  Most people assume that this is offsetting the weights of various cartridges in order to achieve a desired tracking force.  While this is certainly true, it’s also possible in many instances to achieve the same tracking force for a particular cartridge, using different weight combinations.

Using a heavier weight combination (positioned closer to the bearing pivot) will lower the effective mass of the system and shift the resonant frequency ever so slightly upward (e.g. from 10.8 hz to perhaps 11.1 hz).

While you can’t accomplish major shifts like (for example) 7 hz to 11 hz, these subtle changes can be a tuning element and should be considered after you’ve lived with your setup for a while.

Interaction With Other Settings

Tracking force:  if you’ve (for example) increased the effective mass, you may find that you can track a record well with a slightly lower tracing force (e.g. reducing from 1.93 to 1.87 grams)

Loading:  Cartridge loading can have a mechanical damping effect and if you’ve increased the effective mass of your tonearm, it’s possible (unlikely) that you might want to reduce your loading (i.e. increase the impedance the cartridge is working into).

Damping:  if you have some sort of damping adjustment, you may want to revisit the amount you’re applying by reducing damping if you’re increasing the effective mass.