No, 8 ohm is low impedance, used by the military. In every US helicopter I've ever flown, any standard DC headset will work, as long as it's a civilian model. Some European operators use low impedance avionics, for whatever reasons, and you may need to check the individual aircraft to make sure. As for down under, I have no idea what is used, but no matter the location, 8 ohm is low impedance, 300 ohm is high impedance.