I'm no scientist, so my reply is probably too naive, but the notes produced by real instruments are not the same as the notes produced by speakers. The source is different, so it sounds different.
I recently got an LP of Bach's cello suites. It is a single instrument playing and while my set up is hardly big league it is not too bad and I get lots of resonance and richness of tone. But it is not the same as having a real cello playing in the room. What would be pouring out of that cello is something living, and altogether more resonant than anything that can come out of a speaker that is dependent on an electrical signal.
Surely the sound of the cello from the speaker is being approximated by the speaker cones. How could that be the same as the sound produced by the drawing of a bow across a set of strings?
I basically agree with you, but just not for the reason that I
think you're suggesting
In terms of causing air pressure fluctuations that are the same as those that would be produced by a bow being drawn across a cello, a loudspeaker can actually get extremely close. By that I mean that it can produce something very close to the same resonances and harmonics that a cello can, so close that any differences between what the mic recorded and what the speaker reproduces may well be inaudible, or extremely close to inaudible.
The bigger issue is that the signal the speaker receives is either:
- a recording of a cello which contains both direct and reflected sounds from the space in which the cello was played, or
- a close-mic'd or anechoic recording of a cello that contains (more or less) only the direct sound from the cello
If it is (1), upon playback the loudspeaker is forced to be the source of all direct sound
and all reflections, but instead of these coming from different locations around the listening room as they would if a real cello were there, all these sounds originate in the listening room from the location of the speaker.
If it is (2), there's a theoretical problem, because there is no single correct location in an anechoic chamber or with a close mic to record the cello (you can't put a mic at the same location from which the cello produces sound). So you've captured only the sound of the cello as it was at one specific location.
Moreover, the loudspeaker has a polar response that is different from a cello. So when it replays the recording taken by method (2), it will send it out into the listening room with a different polar pattern than the cello had IRL.
This is why, generally, the best a loudspeaker can hope to do is to accurately reproduce what's on the recording - whatever that is - not the cello that was recorded. Notwithstanding this limitation, good loudspeakers can actually do this very well (i.e. produce near identical resonances, harmonics, etc. as contained in the recording of the cello or whatever instrument(s) happen to be present).