What is “warmth” and how do you get it?

You're right. What was I thinking?!?

Once again, more proof of the need for a better audiophile vocabulary; one which, if it is to have any real meaning, needs concensus. A good place to start is, ironically, outside the audiophile world; in real world vocabulary. How often do we say something like :"Joe Toob is a warm person", or "John Fett is not a very warm person, he is cold". When we say these things, are we referring to anything having to do do with frequency response? Probably not. We are probably referring to wether a person is amiable or not. I think the term warm, in the audio context, is being misused, and has more to do with a components ability to draw you in, and let you get involved with the music. Frequency response certainly plays a role, but I think more impotant in determinng a component's "amiability" is the texture of the sound it makes. This can be independent of perceived brightness, or darkness. I have heard components that sound way too dark, and thick through the midrange, but are also very dry sounding. Conversely, I have heard some that I would consider way too bright sounding, but are also very liquid sounding. Texture. Micro dynamics ability is the other key factor. That is where a component's ability to convey a performer's expressive qualities lies; the warmth of the performance.

Music that approaches the sound of a live performance is, by defintion, warm. The sound of live music runs the gamut as far as wether it sounds shrill, bright, dark, etc. It is the human element that makes it warm, or not. What gives music that hard to describe texture, and dimensionality is the human body attached to it.