[bkssed]

Each headphone has a frequency response curve tuned to a taste - they have multiple regions of boosts and reductions in bass mid and treble. A question always comes to mind when looking at fR curves - how designers are able to target the frequencies they want to boost and reduce and by certain amount? Is it just the structure of the diaphragm or has something in the voicecoil too?

 

[Roseval]

Headphone measurement is rather complex.
Not only you have the characteristics of the driver but the reflections inside our ears as well.
A good introduction can be found here:
http://www.innerfidelity.com/headphone-measurements-explained

 

[getclikinagas]

I would like to know this as well.
How is the frequency response of a Headphone/Earphone tuned? And how are specific parts of the FR modified based on the designers preference?
 
I imagine it is a combination of venting, voice coil turns, diaphragm structure, material and coating, magnet used, physical filters etc. But that isn't a specific enough answer.