For definition, the timbre (i.e. the sound we perceive within our mind) is the spectrum on the signal (and its playing envelope over the time).
Thus, a bunch of partials (harmonics and overtones) which different levels each.
The fact is: when we reproduce a recordings, any chain of reproduction will alter these "levels" (by speakers, frequency response or snr; or just different air pressure from source to ear, reflections within a room, and so on), but I can perceive in fact the same timbre impress in my mind, even if levels of these partials will change during the reproductions (and some will also be added, adding "color" to the thole process; but this is another discussion which doesn't matter right now).
So the question is: why, if the spectrum change, I can perceive the same sound (or at least, a major part of it)? Is there any factor that I'm missing? Because, theoretically, the sound I heard should be different every time.
And in fact, there are cases often that I can't hear the same timbre, because this (for the reason above) will be altered.
Is there a sort of "timbre resolution levels" for each person's earing? Of course this task is subjective.