[justAlittleCom]

I think this web page is really superficial, contain some factual error, and miss the important points. - impedance has nothing do to with power. A watt is a watt, impedance is only the ratio between current and voltage. The misconception comes from the fact is that most amplifier are voltage amplifier : the higher the impedance, the less acoustical power you get for the same input signal. But it has nothing to do with electrical power, with a current amplifier it would be the other way around. - sensitivity has everything to do with power, it says how much acoustic pressure you get for 1 watt. When considering "how loud my headphone will get ?" sensitivity is way more important than impedance.

To me, the 3 important things are : - the topology, you dont listen to music in public transport in a open headphone - the impedance, but only because of the matching with the amplifier. A lot of amplifier output impedance are simply too high (mostly for electrical protection as the output can be brefly shorted when introducing the jack), so, the headphone impedance need to be significantly higher. If the output impedance of the amplifier and the impedance of the headphone are close, it will impact the frequency response of the headphone. - the frequency response.