Hi guys - if I may chime in on a couple of things about this harmonica example:
Vertigo wrote: "a harmonica is an instrument that pushes very little air and since it pushes very little air, how it interfaces with the room is probably negligable."
This is incorrect. As any musician will tell you, every room has a very significant effect on your tone, no matter what the instrument. A professional musician can adjust for this variable and still create exactly the sound wanted in most cases, but this sometimes requires a fairly big adjustment. This does not have mainly to do with how the sound is created, by the way (so your speculation about the airstream size is almost irrelevant) - it is almost entirely the effect of the acoustics of the room on any sound in it.
As for this: "Am i missing something but isn't the bottom line this...that what is emanating from the speakers and what i hear from my live harmonica are negligible? (qualifier: the harmonica in my mouth has a different directional point of view since it is inches from my ears.)(but the timbres are negligible)(believe it or not... i don't care)"
One thing that needs to be added here, assuming that you are playing the harmonica, is that the sound you hear will be quite a bit different from the sound anyone else in the same room is hearing, for the simple reason that you, as the player of the harmonica, are also hearing the sound INSIDE your head. Again, this is by no means insignificant. If you record yourself, and listen to the playback over speakers, you will sound different to yourself (basically the same reason your own voice sounds different to you than to everyone else, or to you when you hear it recorded).
This is why musicians do not rely on their ears alone - we are constantly asking others to go out into the hall and listen to what we are doing for confirmation that it is indeed sounding exactly how we think it is. This is especially the case for my own instrument, the horn, since we have the additional circumstance of our bells facing backwards, but it is true of all instruments. We also record ourselves for the same reason, to make sure that we sound exactly like we think we do. You will also hear very tiny "impurities" in your sound, usually extraneous noise that your body is making along with the production of your tone that is not actually part of your tone, and which are inaudible to anyone else, even someone sitting right next to you, and which will not be picked up by the mike, even if it is placed ridiculously close, as digital mikes often are, but that's a whole other issue. You learn to separate these noises when critically listening to the sound you are producing. This is one of the main things that serious music students have to get used to - the fact that you do not hear your own tone exactly as everyone else does. But the main point is, no, the difference between what is emanating from the speakers and what you hear from your live harmonica will not be negligible, especially if you are talking about your own playing.