That ain't technical background, that's marketing speak :-).
Again, both the Eminent and Ortofon SPU Synergy (you can find these on the cartridgedb.com site) have a 1.8-ohm coil impedance and produce 0.5mV (measured at 5cm/sec). If we apply the sqrt 2 conversion factor (3.54 vs. 5cm) to the coil impedance, we see that putting a 2.5 ohm coil into the SPU Synergy or Eminent would yield 0.5mV @ 5cm/sec. No need for a yokeless magnetic circuit, just a suitable core material (and appropriate coil design) :-).
And FWIW, since the diameter of the coil wire can be either thicker or thinner, you cannot simply look at the coil impedance and deduce that the coil weight is lighter. A higher-impedance coil could be the one that's actually lighter, depending on the coil wire diameter specified.
Now don't get me wrong, I'm not trying to knock yokeless designs (I like them, too). But trying to draw a connection between yokeless and greater efficiency (output vs. impedance) isn't warranted, IME.
regards, jcarr
Again, both the Eminent and Ortofon SPU Synergy (you can find these on the cartridgedb.com site) have a 1.8-ohm coil impedance and produce 0.5mV (measured at 5cm/sec). If we apply the sqrt 2 conversion factor (3.54 vs. 5cm) to the coil impedance, we see that putting a 2.5 ohm coil into the SPU Synergy or Eminent would yield 0.5mV @ 5cm/sec. No need for a yokeless magnetic circuit, just a suitable core material (and appropriate coil design) :-).
And FWIW, since the diameter of the coil wire can be either thicker or thinner, you cannot simply look at the coil impedance and deduce that the coil weight is lighter. A higher-impedance coil could be the one that's actually lighter, depending on the coil wire diameter specified.
Now don't get me wrong, I'm not trying to knock yokeless designs (I like them, too). But trying to draw a connection between yokeless and greater efficiency (output vs. impedance) isn't warranted, IME.
regards, jcarr