That 's a very debatable matter, sounds like the other guy's definition of xmax is , coil length minus gap height divided by two equals xmax. Well that only works for one motor topology, long coil with short gap height. I believe the rl-i10 uses TC Sounds TC2+ motor, which is of the long coil / short gap height design. However TC does not measure xmax by that formula, their definition is 70% of BL (which in my mind is the only reasonable way to measure xmax). It would seem to me that using that method of xmax measurement could require a coil quite a bit longer than 50mm just my $.02