"Air" is one of those audio terms that means different phenomena to different people. That's why I prefer S.H.'s term "breath of life" and even then, some think he's referring to the human voice which he isn't necessarily.
Steve's bottom line for system sonics is: if you don't have lifelike midrange, you've got nothing. If you think about it, that's why, for example, the Quad 57 ESL is still considered one of the great speakers of all time and a standard for perfect midrange. Though it lacks extension (in both directions!) that midrange just hooks you and you forget about its shortcomings.
Steve's bottom line for system sonics is: if you don't have lifelike midrange, you've got nothing. If you think about it, that's why, for example, the Quad 57 ESL is still considered one of the great speakers of all time and a standard for perfect midrange. Though it lacks extension (in both directions!) that midrange just hooks you and you forget about its shortcomings.