[faileas]

Just something i've been curious about. Most of the knowledge i have of circuits i have is in the DC domain, so any EEEs please forgive any gross errors i make. In addition, for the most part, i'm a full sized headphone user, who has never really needed to use one of these devices
 
As i understand it, 'impedance' is the property of a element in a circuit to resist a alternating current, and tends to be a complex number - which leads to my first bit of confusion - since headphone impedances are not in the form of a complex number.
 
An impedance adaptor is simply resistors placed in the signal path- often with IEMs - in short its being used to limit the volume, as opposed to changing to real impedance of that form of circuit... OTOH, a resistor DOES have inductance, but measuring it is is not as simple a matter as it being the same as resistance..
 
so which is right? does one pick resistors primarily to attenuate, or is there some other criteria behind it?

 

[Mad Max]

It also affects the impedance curve of the headphone which in turn affects the sound, sometimes negatively, sometimes positively, it depends.