Firstly it has to exist on the recording -- minimally miked recordings of acoustic instruments in defined spaces are best
Secondly careful control of room acoustics to manage reflections and let you hear through to the original recording
Thirdly careful control of vibration throughout the system to avoid the interferences from that source
And finally be careful that what you are hearing is not an artificial "bloom" or halo that some components (particularly some tube designs) impart -- while attractive it is a coloration -- the same can also occur if the mid range is boosted in some instances, some instruments can suddenly appear to "pop" but again this is a coloration
Finally if you are hearing lots of isolated instruments hanging in space in their own pockets of air this is either a) a system derived coloration or b) a design choice by the recording producer, but in either case is artificial. What you are ideally looking for is a collection of instruments/performers clearly related to one another in space. I find well recorded string quartets to be a great way of telling if you are getting the former or the latter -- the isolated and emphasised sound is very attractive, but it's not true to life
That’s what the hobby is all about. There is no single answer. Air, sweetness, liquid-ness, soundstage, transparency, bass slam, they’re all part and parcel of signal to noise + distortion ratio S/N+D for which there is no substitute. Get your mind in gear and your ass will follow. - old audiophile axiom
The ambient sounds of the area the recording was recorded in. By area ...indoor (Studio) vs indoor (concert hall/non-studio building) vs. outdoor area. Some like to call this "air" which is fine, but it would seem that the "sound" of the recording area is most likely that "air".
Lowering the noise floor by having clean power through the mains will reveal air and ambience on the recording. Also vibration control on components and rack, and an acoustically treated room will reveal air and more in the recordings.
Get better speakers. Most speakers have horrendous time coherence.
As a former recording engineer, I can tell you that there is no 'air' in the studio. In good rooms like Paramount, Sky Walker, Hit Factory, Oceanway, Capital A, etc. an acoustic guitar or piano sound much as it does in a small club.
Great answer by @folkfreak regarding setup of a system. And air can only be heard if it's in the recording. @ieales provides good comments about studio recording. The "air" and sense of space is artificially created by the engineer. But in a venue such as a church or the Musikverein concert hall there is natural reverb. But the end result of "air" and space on the recording is created by natural and artificial reverb, and only with proper mic'ing of acoustic instruments.
The PSB Imagine T2's are decent speakers which produce a wide and deep soundstage and are capable of disappearing. However, they are not very detailed. If you are not getting the desired effect from recordings, the problem may lie upstream or with your room acoustics.
When they went all digital TV they lost the air that was there in abundance with the analog signal, a huge spacious soundstage, especially noticeable on live football 🏈 baseball ⚾️ and olympics ⛷ broadcasts. Very similar to the difference between tape and CD, now that I think about it. Tape breathes, it’s a natural medium. When you can breathe you get more...air. 🤗
Sorry but I just can’t resist saying this. Don’t pounce on me as it’s a joke. The only time I heard air around the notes was when some guy farted very loud in the listening room. We could also smell the “air” as well