@VJJ your raised a lot of questions, lots of good questions. I think it’s unfortunate that there isn’t a more authoritative text book purely about headphones which addresses a lot of the common audiophile questions and misconceptions. Forums are better than nothing, but information is often hearsay, unverified, and obviously scattered all over the place.
I would recommend reading some text books such as ones by Toole to get a better understanding of how transducers work. Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms (Audio Engineering Society Presents): Toole, Floyd E., Toole, Floyd: 9780240520094: Amazon.com: Books
And this:
That’ll shed some light on questions about driver “speed”, technology, and measurements. I’ll leave the detailed and correct responses to others more qualified and eloquent than me. Let’s just say that you’ll find a lot of your answers by finding out what the following means: headphone acoustic impedance, minimum phase system, distortion measurements and audibility, upper range limit of frequency response of transducers.
If you don’t want to read text books I have some papers you might find interesting:
The Measurement and Calibration of Sound Reproducing Systems:
Listener Preferences for High-Frequency Response of Insert Headphones
Personalized and Self-Adapting Headphone Equalization Using Near Field Response
Modelling Perceptual Characteristics of Prototype Headphones
A Comparison of Sensory Profiles of Headphones Using Real Devices and HATS Recordings
Perceptually Robust Headphone Equalization
for Binaural Reproduction
https://www.researchgate.net/publication/226629941_Perceptually_Robust_Headphone_Equalization_for_Binaural_Reproduction
A Study of Listener Bass and Loudness Preferences over
Loudspeakers and Headphones
One main point which you’ll certainly come across and could get confused about is “everything is just sound waves (frequency response) at the ear drums”. While it might seem obvious that we hear with our ears, we haven’t seen much research using direct measurements at the ear drums, especially not in terms of audiophile’s concerns of “sound stage” “attack” “punch”. Other factors such as activation of skin outside of the ears by headphones could potentially play a role in how we perceive sound. All of the above requires more research, and there are currently no clear answers.
Which brings us to one interesting point about sound quality research. You’ll basically NEVER find any papers or researchers talk about “sound stage” “attack” “dynamics”. These are all audiophile terms which are ill defined at best. Some headphone designers will talk about the feeling of spaciousness, and that is one term which is better defined and understood. It’s got to do with low acoustic impedance and large driver size.
One last point on my wall of text in response to your wall of text: Sound stage on headphones while playing back stereo content is basically just an illusion. Bi-aural recordings and playback with customized HRTF EQ is what would give realistic localization effects.