No they don't activate on high impedance which is a shame, I did manage to get a taste of high impedance sound with these just messing with the phone settings but only for a few seconds. (an accident really) and those few seconds sounded AMAZING. With the Equalizer app I can push the levels up with the sound amplifier. Though as mentioned in this thread already, there's a easy high impedance hack that you can not do with headphones like the M50 but you could with the M50x. Reason being thAt the 50x cables are detachable, the original M50 are not. The easy hack as explained here in this thread, is to plug in the cable to the lgv20, then plug them into your headphones, and that somehow puts the lgv20 into high impedance mode. That's what I understood, someone please chime in if I'm wrong.
(look up post #25)