My 22 year old son is visiting while on break from school. For the last 5 years, his music listening has been through headphones only. I've made a couple of very startling observations. He cannot tell the difference between M3, M5, M50 and M100. They all sound the same to him. He also cannot perceive soundstage depth through any of my speakers.

I conclude therefore his continuous headphone listening has damaged his synapses responsible for certain auditory cues.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated