What makes the Bloom around instruments . . .

Chuck, the quote you posted from Rtn1 is as good a description of the quality called "bloom" as I have ever read (though as Elizabeth said, many call it "air," an even more vague term). To me, this is one of the most undefinable of all audio reproduction factors. I think a combination of elements contribute to it - Elizabeth, Noble, Bryon, Baranyi, and others all made good comments on it. To me, these factors add up to much more than one term could describe, but if some want to call it bloom, so be it - it has to be called something, if we are going to discuss it. For me, and for many fellow orchestral musicians, this is one of the most important qualities of sound reproduction - this bloom factor goes a very long way towards determining how "real" a system will sound. Digital and solid state have a very hard time reproducing this particular quality of instrumental and vocal timbres - as I have said before, I think it has a great deal to do with how much of the harmonics/overtones of/in these timbres are reproduced.

I have never heard one of those Pass amps - I would very much like to someday.

Frogman and Swampwalker, love your additions to this conversation! I agree, Swampwalker, that one rarely hears "bloom" from a recording done in a studio. I think this goes a long way towards explaining why it is present on some recordings and not others. Good concert halls are of course designed to get the maximum "bloom" from the instruments and voices performing in it, whereas the recording studio is designed so that the recording engineer can make the recording sound how he wants it to - they are generally quite dead, and therefore usually kill "bloom." This is why so many studio recordings have that fake reverb added, to try to get some of that quality back, very unsuccessfully.